Gut Health Expert Dr Will Bulsiewicz’s Interview on DOAC Podcast (Transcript)

But now in my work with Zoe as their US Medical director, I’ve been heavily involved in clinical research.

STEVEN BARTLETT: Again, you mentioned a big G word there, gastroenterologist.

DR WILL BULSIEWICZ: Yeah.

STEVEN BARTLETT: What is that?

DR WILL BULSIEWICZ: We are the specialists in terms of basically like the intestines, the gut. So if I were to summarize it, I would say “guts and butts.”

The Missing Piece of the Health Puzzle

STEVEN BARTLETT: The conversation around the gut microbiome and the gut generally has exploded really since sort of 2000 and 2006, 2007, time before then. I mean, to be fair with you, I think as far as I’m aware, and I’m not that close to doctors or hospitals or research, I’ve only started hearing about the gut microbiome in the prevalence that I have in the last two years.

What is the central misconception that most people have as it relates to their health? That guy that looks into the mirror and goes, “I don’t like what I see here. I don’t feel good.” That’s curled up, they’re bloated, they’ve got gut pains. The current sort of line of thinking will say it is X, but there’s something that you believe it is. What is that?

DR WILL BULSIEWICZ: Well, I think that all of these things ultimately connect back to our gut microbiome. And I think that’s the piece of the puzzle that’s been missing this entire time. There was sort of this black box. If you eat well, you will improve your health. If you do this, you will improve your health.

What we were missing was the understanding that all of those choices ultimately impact these gut microbes. And by impacting these gut microbes, you can actually transform the physiology within your body.

STEVEN BARTLETT: Gut microbes?

DR WILL BULSIEWICZ: Yeah.

STEVEN BARTLETT: What is that?

Understanding Your Microscopic Partners

DR WILL BULSIEWICZ: Gut microbes is my nerdy way of talking about these microorganisms that, like, you can’t see them right now, but they’re there. If you hold up your thumb, literally on your thumb, there are as many microbes as there are people in the UK. And they cover our entire body, from the top of our head to the tip of our toes. Every single external part of our body is covered with these microbes.

But the main spot is actually deep inside of us, which is our colon, the large intestine. In that spot you can find 38 trillion. Now these, when I say microbes, it’s referring to the fact that they’re microscopic and they’re alive. It’s mostly bacteria. In addition to bacteria, could also be fungi, could be parasites, could be viruses. But we have 38 trillion of these, mostly bacteria focused and concentrated within our colon. So when we talk about the gut microbiome, we’re really referring to them.

STEVEN BARTLETT: How did they get there?

DR WILL BULSIEWICZ: So you started in your mother’s womb, and evidence these days would suggest that you’re already starting to come into contact with these microbes, but for the most part, you haven’t really met them yet until the water breaks. And in that moment, for the first time, you are exposed to the world and the world is covered in microbes. Everything that’s alive, everything has a microbiome. Could be a plant, could be an animal, could be an insect, could be us.

So when mom’s water breaks, these microbes then enter into the uterus and you meet them for the first time. But you are particularly exposed to them as you pass through the birth canal. And this is basically like nature’s way of being, like, “Hello, welcome to the world and meet your partners. They’ll be with you for the rest of your life and they’re here to help you and they will make you healthier.”

And this is the result of co evolution that goes back over a billion years. We have been evolving, which is crazy, because humans have only existed for 3 or 4 million years. But these microbes were the first life on the planet. And all life evolved with these microbes. And things like, for example, our immune system is the product of evolution that started a billion years before humans even existed.

You Are a Super Organism

STEVEN BARTLETT: We always think of ourselves as one organism. But you’re making the case that I’m maybe 36 trillion or whatever you said, organisms in one.

DR WILL BULSIEWICZ: And we would call you a super organism. And that sounds like a Marvel character, which is cool, and we’ll take that. But that’s actually completely true, because the issue is that if we withdrew these microbes from you, if you were like, hypothetically, we could talk about the bubble boy from the 1970s where they actually did this. They tried to have a child live in a sterile world because he had a specific immune deficiency. So their thought was, if we keep him separate from all the bacteria, then he’ll never have a problem. But the issue is that there are consequences.

There are consequences to living without microbes because we need them. And through this process of co evolution, literally from the very first human, we grew to trust them. And we trusted them with things that are critically important to us and our success as humans. And we allowed them to integrate into our physiology in a way where, once again, if we don’t have them, we’re in trouble.

And that includes things like digestion, breaking down our food, which to me is like, that’s the essence of life. Like, you can’t get energy into your body without this. And they help us to accomplish that. But they also train our immune system. We talked a moment ago about what happens when you’re born, and that’s the very beginning of training your immune system. And during those first three years of life, it has a massive impact on whether or not you develop allergic issues, autoimmune issues down the road.

They affect our metabolism. Our research at Zoe has overwhelmingly shown that they play a critical and essential role in controlling, for example, your blood sugar, your blood fat response after a meal. They affect your mood, literally your energy levels, whether or not you suffer from depression, your cognition, your memory, your ability to focus, all affected by these microbes.

They affect our hormones. So in women, conditions like endometriosis, polycystic ovary syndrome, associated with damage to the gut microbiome, in men, erectile dysfunction, which, I mean, to be honest, is not talked about enough, perhaps because we’ve stigmatized this. But the guys that have this issue, this is like the most important issue to them.

And so when you think about all these things, whether it be digestion, our immune system, our metabolism, our hormones, our mood, our brain health. Like, to me, this is an overview of everything that matters for human health from my perspective as a medical doctor.

Your Unique Microbial Fingerprint

STEVEN BARTLETT: And is my gut microbiome different to yours? Do we all have different sort of jungles inside of us?

DR WILL BULSIEWICZ: We are all different, and this is one of the things that makes us actually profoundly different. So to be honest, this is mind blowing. If we looked at your genetic code and my genetic code, even though clearly we are different people, our genetic code would be 99.99% the same. It’s a small part of our genetics that is different between us as humans.

But our microbiome, these 38 trillion microbes that are living inside of us, they can be completely different. So as a classic example, let’s pretend that you have a twin brother, identical twin brother. So you share the exact same genetic code, you share the same mother. For the vast majority of cases, you would have shared the same childhood and largely the same upbringing in food and things like this.

And our research shows that only about 25% of your microbes would be shared, even though you come from the exact same place. You would be 75% or more different. So you and I, it’s hard to say exactly. Like, if our diet was quite similar, then we would have a more similar microbiome, but it still would be more different than the same.

The Disease Connection

STEVEN BARTLETT: And how much then? So I’ve got twin, we’ve got completely different gut microbiomes, these sort of microbes that live inside our bodies. How much of our microbiome can be associated back to disease and things like that? In your view, what percentage of disease do you think links back to the gut microbiome?

DR WILL BULSIEWICZ: Well, it’s hard to say globally, right? It’s hard to give an exact number. You would have to, I think, go condition by condition to say. But what I would say is this. The reason that I became very interested in this as a gastroenterologist is that I was convinced, and I continue to believe this to be true, that every person that walked through the door to see me had a gut microbiome problem, right?

People with irritable bowel syndrome, Crohn’s disease, ulcerative colitis, celiac disease, acid reflux, go down the line. Every single one of these, when we study them, we discover that they have gut issues. But the other thing, if you expand that, one of the things that I would always do, I’m about to go see a patient, I’m going to walk into the room, and you take the chart off the door. If you’re the patient, you hear that you’re in the room, and you hear the chart come off the door, and the doctor flips it open.

And what do I do? I take a look at their medical history. And when you look, what you see is a laundry list of conditions that have been associated with damage to the gut microbiome. So they’re here to see me for their digestive problem, like irritable bowel syndrome. But when I take a look, I see that they have hyperlipidemia, high blood pressure, type 2 diabetes, history of major depression. They may have autoimmune condition.

And then it starts to implicate these different systems that, like, we have not classically associated immune, like autoimmune issues or metabolic issues or cognitive issues or mood issues. We haven’t classically associated those things with the gut microbiome. Yet they are. And so to me, do I need, like, for that particular patient, do I need a poop test to tell me that they have a damaged gut? Absolutely not. It’s already clear.

STEVEN BARTLETT: And what’s the relationship between our gut microbiome and our immune system? I was reading in the introduction to your book that 70% of the immune system is the gut.

The Gut Barrier and Immune System Connection

DR WILL BULSIEWICZ: Yeah. The walls of your intestine are actually the home of your immune system. We classically would think of the bone marrow as being the place where the immune system exists. That’s not true. That’s where the immune cells are born there. But then they basically emigrate out, and then they take up residence and live within the walls of your intestine.

And by the way, this makes complete sense from an evolutionary perspective because our gut is actually the most vulnerable part of our body. This is where we come into contact with the outside world. Your skin, you may think of that. No, your skin is a wall. Your gut is the place where actually you are making decisions. Do I absorb and allow this into the body, or do I reject and keep it outside?

And in order to help facilitate that, yes, we need our immune system there. But the other thing that we need is we need a barrier. We need something to basically section off the inside of the intestines and keep things separate. So what we have is called the epithelial layer. And this is quite humble, like, given how important this is in our body. It is just a single layer of cells that are being held together by this kind of cement called tight junctions. They stick together.

On one side is 70% of your immune system. On the other side are 38 trillion microbes. And when this barrier breaks down, this is how things that are inside your intestines can get access to your body, get into your bloodstream, potentially cause a whole body infection, and then the immune system is forced to react.

And when this is like, we have an infection, that’s really important. This is why we have an immune system, to protect us in that setting. But what’s happening in the 21st century, what started in the 20th century is chronic inflammation. And chronic inflammation is the result of a broken barrier.

When that gut barrier breaks down now we are giving access to our body to things that aren’t supposed to get access. And the result is that the immune system stays perpetually active because it is constantly trying to clear stuff out because the barrier is broken. And for those who are wondering, so, Dr. B, then how do we fix the barrier? Not to put the question into your…

STEVEN BARTLETT: Mouth, Stephen, but please do.

DR WILL BULSIEWICZ: The answer is the microbes. The answer is the microbes, because they are the stewards of the gut barrier. They help to repair it. Every three or four days, you actually completely transform and recreate your gut barrier. So it’s not the one that you were born with, it’s the one that you developed in the last three or four days. And you will turn that over. And when it turns over, we need these gut microbes to help us to form a strong gut barrier. So because it’s constantly turning over, this is where the microbes come in, and they’re critically important.

Microbe Turnover and Replication

STEVEN BARTLETT: Again, the microbes, when you reference microbes, you’re talking about the bacteria, the yeast, the parasites, the viruses that exist in our guts. And how long do they live for? You said they turn over in three days. Does that mean that they live for three days? Typically.

DR WILL BULSIEWICZ: So the gut barrier turns over every three days? Yeah, yeah. And those are human cells. So those are not the microbes. Okay, so those are your human cells keeping the microbes separate from your immune system and your body. These microbes, they are turning over, literally every 20 minutes.

STEVEN BARTLETT: They’re dying every 20 minutes.

DR WILL BULSIEWICZ: So. Well, not necessarily dying.

STEVEN BARTLETT: Replicating.

DR WILL BULSIEWICZ: Replicating.

STEVEN BARTLETT: Okay, Right.

DR WILL BULSIEWICZ: And so if we think about this, if you had one microbe in your intestines right now, and we feed it something, whatever it may be, good thing, bad thing, whatever. 24 hours from now, that microbe will have spawned at least 1,000 new microbes. So if you think about the power that exists there to amplify choices, starting with one and ending 24 hours later with a thousand it’s crazy.

Food as Medicine: The Power of Daily Choices

STEVEN BARTLETT: There’s this really interesting sort of reframing in the introduction of your book, which is really simple, but it does cause you to. I think it’s a really powerful frame to think through about what we eat and how we eat, which is where you say that each of us consumes an average of 1.3 kilograms of food per day.

Keeping the math simple, that’s 475 kilos of food per year, meaning we’ll consume about 36,300 kilos of food during our lifetime. And in contrast to the couple of milligrams of medicine that we take, it really makes you realize that food is in fact the medicine that we’re feeding our body at all times.

We think we sort of compartmentalize food over here as this energy source that quenches hunger. And then we have medicine over here to fix stuff. But in fact, you’re doing 36,000 kilos of food in your lifetime. So the thing that’s having the biggest sway on your medical, your sort of physiological health and your gut health is of course the food. The food is the medicine.

DR WILL BULSIEWICZ: Well, and I think that there’s two important takeaways from that. Because there was a study actually that changed my life in 2014 that came out. This was published in the journal Nature, which is literally the top journal on the planet. And the author was Lawrence David from Duke University.

And you have to understand, if we go back, this is almost 10 years ago, in this moment, we didn’t know if food changed microbes in humans. We didn’t know this. This is new information. We knew it in mice, but it’s not the same. Mice are not humans.

So what they did to try to prove this is they put people on diametrically opposed diets. So a completely 100% plant based diet versus a completely 100% animal based diet. It was only a five day study, which is interesting because within five days you can actually see massive results.

And one of the key takeaways from this study is that the choices that you make today within 24 hours will have an effect on your microbiome. In that study, when they changed a person’s diet, 24 hours later, you could already see things underway, shifting.

So now the other thing to keep in mind here is that I think is really important is the gut is forgiving. I mean, to a degree you can only beat it up so much, but the gut is forgiving. So this doesn’t mean that there are foods that are on the table and off the table. Everything is on the table. But what we want is we want to create a weight or a disproportionate consumption of those high quality foods. Because when we do, we are lifting these microbes up.

How Food Feeds Different Microbes

STEVEN BARTLETT: Explain that process of food and the impact it has on the microbes. So is it watering certain microbes? Is that a way to think about it in simple terms, these microbes are.

DR WILL BULSIEWICZ: As alive as you and I are, Stephen, and we need to eat. If I don’t eat, I get quite hangry, and they do too. But it turns out that the reason that they took up residence, because they could have been anywhere, they could have stayed inside soil or lived on a plant or something like that, they chose to live inside of you.

And the reason why they are inside your colon is because they get access to nutrition. You do that for them. You go out, you find food, and you deliver that to them. Whatever goes into your mouth, whatever it may be, it will come into contact with these microbes and they will consume it. And this becomes their energy source. Because they are alive, they need energy.

But the choices that you make impact which microbes get to eat. So not every single microbe likes kale. Not every single microbe likes sugar, but there are some that like sugar and some that like kale. And when you make these choices, whatever it may be, those choices ultimately are going to feed specific families of microbes, lift them up, and allow them to thrive.

So when we talk about, you know, improving dietary quality, and you hear me talk about this in Fiber Fueled, which is a message that I started sharing publicly back in 2018 and the book came out in 2020, or if you listen to Tim Spector, who published the paper that I’m about to talk about, the science is clear. The way to lift the microbes up is by eating a variety of plants.

Now, in Tim Spector’s paper that originally came out, it’s called the American Gut Project, but by the way, the British Gut Project was a massive and critically important part of the study. In that study, you have to understand, the magic number that they came to was 30. A lot of that had to do with just the technique that they were using to measure it. Doesn’t mean that 29 is bad and 30 is fantastic. It’s all on a spectrum. 30. 30 different plants per week. Yeah, 30 different plants per week.

So the key is we want varieties of plants. And every single plant’s choice ultimately is fuel for a healthy gut microbiome. So that’s fruits, vegetables, whole grains, seeds, nuts, and legumes it’s not just veggies, it’s not just kale.

And to me, one of the things that I’ve always tried to do, whether it be as a medical doctor or as an author, I want to meet people where they are. So, if I were consulting with you, I want to know where you stand right now. And then we’re going to set realistic goals. So for a person who’s eating 10 different plants per week, which by the way, is more than I was eating 10 years ago, to go to 30 instantly, that would be quite hard. And when it’s hard, it’s more likely to become unsustainable. I would go from 10 to 15. And when you hit 15, I would be celebrating.

STEVEN BARTLETT: How many plants does the average person eat in the Western world? America, the UK, Europe? Do you know?

DR WILL BULSIEWICZ: I believe in the American gut project, the number was around 10 to 15 for the average person. It was a minority of people that were hitting 30 per week in that study.

Personal Experience: Microbiome Diversity

STEVEN BARTLETT: It’s interesting, when I did my Zoe test, I got my results back and it did say that I had quite a narrow gut microbiome in comparison to my partner. And I was thinking about this, I was like, you know, whenever we go somewhere, whenever we go to a restaurant, she orders new things all the time.

And if you look at our fridge, it’s like tahini and this and all this, all these plants, especially in the top part of our fridge, it’s all fermented stuff. She eats like, she’s like a rabbit or she just eats anything and she eats diverse food and she orders new things.

And then there’s me. I like what I like. And if I go to a restaurant, anyone that’s been to a restaurant with me, three times could order for me because they know until I got my Zoe results back.

DR WILL BULSIEWICZ: And it was.

STEVEN BARTLETT: It was pretty alarming because she had. Her microbes were like the Amazon rainforest.

DR WILL BULSIEWICZ: Nice.

STEVEN BARTLETT: And mine were like, you know, a park at the end of the street.

DR WILL BULSIEWICZ: You know, I think that it’s important to start with food that you like. Yeah, we’re all like that. What you described. The issue is finding that motivation to push yourself. To me, this is the piece of the puzzle. Again, this was a black box. We didn’t know anything about the gut microbiome. We just had nutritional ideas being tossed at us.

Now this is filling in the gaps where it’s like, hold up. No. Nutrition affects the microbes. The microbes affect us as humans. Now we can connect those dots. And to me, I find this very empowering and motivating to know that that exists and to know that those choices, every single meal, is an opportunity to follow this concept and add more diversity to your plate.

But the other thing is, you mentioned that your partner is eating fermented food. That is a lost art. People have not been consuming fermented food in the Western world. And the research is quite clear and standing out at this point that actually there was a fascinating study out of Stanford University randomized control trial. The intervention was to add fermented food to the diet in people that had not been consuming fermented food.

And what they found eight weeks later is that they had increased the diversity within their gut microbiome. What does that mean? If your microbiome is the park at the end of the street, adding fermented food, we can make it into a jungle.

STEVEN BARTLETT: Give me some examples of fermented foods. And what is the fermented part? What does that mean?

The Microbiome of Food and Fermentation

DR WILL BULSIEWICZ: Well, first of all, we mentioned that all life on this planet has a microbiome. So there was an interesting study where they analyzed the microbiome of apples and discovered that when you eat an apple, like, you just grab an apple off the fruit bowl, that apple has about 100 million microbes that are a part of it. So they’re already there. And those microbes have been a part of the apple’s life, helping it to grow from a flower to a fruit.

So now these microbes, they are also involved in the life cycle of that apple. So when the apple goes to spoil, the microbes are the ones doing that. In fact, I would argue that when food spoils, I actually find that reassuring. If food doesn’t spoil, we should be concerned. The microbes are helping to facilitate that spoilage that takes place, and that’s because the Earth is taking it back. It’s this. It’s the cycle of life that’s going to turn into dirt.

Right now, fermentation is where we actually grab that process and we control it. Almost like a magician, we’re shaping it. And what we’re having is we’re empowering certain microbes to protect that food so it does not spoil and they transform it.

So if you were to take cabbage, you don’t need to do anything special to this cabbage. You literally just buy cabbage, perhaps at your farmer’s market, chop it up, put it into a mason jar, pack it in there, and add a sea salt brine solution, a saltwater solution, and you basically put this into a nice, cool space. Give it a week, you will have sauerkraut.

Sauerkraut is not salty cabbage. It’s tart, it’s bitter, it’s acidic, it’s delicious. When you make it yourself, it is completely different than the sauerkraut that I grew up on that came from a can, which was soft and disgusting.

So this is what fermentation is. It’s transformation. The microbes, specifically bacteria and yeasts, are transforming the food for us. And when they do this, they also are eating. So because they eat, they grow stronger and they multiply. So you are creating a food that is high in microbes, which we could call probiotics.

It has been transformed to unlock the nutrition, which we could call prebiotics. Prebiotics are the parts of our food that actually feed the microbes inside of us. It’s their food, prebiotics. And they are releasing new chemicals that can have beneficial effects on your body, which we call postbiotics. You find all of this in that one jar of sauerkraut. So that, to me, is a superfood.

And it could be sauerkraut, it could be kimchi. Pickles, like pickles are not meant to be a vinegar thing, by the way. Vinegar is the product of fermentation. But pickles were never meant to be “Hey, add cucumbers and some vinegar and call it a day.”

STEVEN BARTLETT: True.

DR WILL BULSIEWICZ: Pickles are meant to be that. You take the cucumbers, you don’t skin them, you allow the microbes that are on the surface to do their job, and you put them into a saltwater solution with some dill, some garlic, black peppercorns, and a couple of days later, you will have a pickle.

Understanding the Three Biotics

STEVEN BARTLETT: I want to make sure I’m super clear on those three biotics that you mentioned. So prebiotics are the food for microbes. Probiotics are the microbes themselves, and then postbiotics are the compounds that the microbes make. Is that roughly accurate?

DR WILL BULSIEWICZ: That’s roughly accurate. And there’s a minor caveat, which is that for these things, prebiotic and probiotic, they have to have beneficial effects on humans in order to count. So we can’t call it a prebiotic because it has just an effect on microbes. Sugar has an effect on microbes. It’s not a prebiotic.

And the same is true for probiotics. Now, the original conception of probiotics that most of us have, it comes from a capsule, right? And the reason why we can call it that is because we have demonstrated through clinical studies that the specific types of bacteria or yeasts in some cases that you find in that capsule have been proven to be beneficial to humans.

STEVEN BARTLETT: So the prebiotic is a food, the probiotic is actually alive and then the postbiotic is not alive. That’s a compound that’s produced by the things that are alive.

DR WILL BULSIEWICZ: That’s right. And the key with all of this is the postbiotic. So one of the… And these can be things that are completely beneficial and good to us as humans. An example of this are the short chain fatty acids. Short chain fatty acids are the product of consuming fiber or resistant starches and they come into contact with your microbes. Again, you would not be able to get these if you were sterile.

STEVEN BARTLETT: Can I just drink them in a can? Postbiotics? Is there not a can of postbiotics that I can just drink?

DR WILL BULSIEWICZ: Well, so they’re coming out now with supplements that are these postbiotics in some cases. And the issue that I’ve taken with them and I’ve actually discussed with some people within the supplement industry, let’s not assume that that’s going to do the exact same thing that eating a high fiber diet is going to do. It’s not the same.

The Power of Postbiotics

STEVEN BARTLETT: So let’s then talk about what happens with those. I’m assuming that the postbiotics compounds are the things that have all the health benefits. So the reason why the gut microbiome is so healthy, the reason why these microbes are so beneficial is because they produce postbiotics. And these postbiotics help our body in various ways.

DR WILL BULSIEWICZ: Yes. So we mentioned earlier, we were discussing how we have this gut barrier that’s key to protecting our immune system. And I mentioned that the microbes are the stewards of that barrier. It’s the postbiotics. It’s the short chain fatty acids, butyrate, acetate, propionate that are produced by these bacteria that builds the wall.

When you want to build your wall and protect your body and reduce inflammation, you need more of this. Now that’s not the only thing that they do. Those postbiotic short chain fatty acids also directly affect your immune system, directly affect your metabolism, get into your bloodstream, pass throughout your entire body, cross the blood brain barrier. They have the ability to actually get access to your brain and can affect your brain.

And we could talk about different ways that they can do that, but the point is that this is what really matters, because the microbes produce these chain fatty acids and then these short chain fatty acids have healing effects throughout the entire body. And when we see human studies looking at fiber consumption and showing us how beneficial fiber is to us as humans, I want everyone to understand the reason why fiber is beneficial to us as humans is because fiber comes into contact with microbes and those microbes release short chain fatty acids. That’s what’s happening.

The Gut-Metabolism Connection

STEVEN BARTLETT: Metabolism. Metabolism is the… I’ve been learning a little bit about metabolism recently. When people think of metabolism, they think of the speed in which I process my food. So people in society say I’ve got a high metabolism, which means they’re probably going to be quite skinny. A low metabolism means, I’m probably going to take longer to process my food. What is the role between the relationship between my gut and my metabolism? And have I defined, I’ve probably defined a metabolism wrong there, but what is the relationship?

DR WILL BULSIEWICZ: Well, metabolism is basically dealing with the currency of energy and it is the engine that drives us as humans. How do these microbes affect our metabolism? Well, we have research at Zoe looking at this directly called the Predict 1 study in that we were looking at what is the thing that tells me, predicts what your blood sugar response is going to be to this food or your blood fat response after a meal.

And when you start to line these things up, they’re individually different, they’re not the same. But if you look at both of them, the gut microbiome plays an essential and critical role in each. So in other words, if we know what your gut microbes are, then that empowers us to be able to understand why you have high blood sugar, why you have low blood sugar.

Now, if we want to get super nerdy and detailed into the weeds, a little bit of how this is actually happening. It does come back in many ways to these short chain fatty acids. They’re not the only thing we’re, in some ways we’re reducing it a little bit too much. So I just want to be clear to everyone, there’s other things going on too, but these short chain fatty acids, they have the ability to basically activate certain receptors and cells that will basically allow us to have more sensitivity to insulin, to reduce fat storage, to enhance fat burning.

So at the end of the day, when we think about these sort of measures of metabolism, because there’s certain things, blood sugar response, blood fat, cholesterol levels, visceral adiposity, meaning fat that exists around our stomach. When you look at all these things, the gut microbes play an essential role in regulating every single one of them. And the short chain fatty acids tend to be the key.

The Importance of Looking at Your Poop

STEVEN BARTLETT: I read in your book that 60% of poop is bacteria, which just blew my mind.

DR WILL BULSIEWICZ: Yeah. And I think that this is an important conversation to have. Because we have stigmatized poop. We’re not allowed to look in the bowl. We should be looking in the bowl. And the reason why is because if I were a cardiologist, I would come over and I would check your pulse, I would listen to your heart, and those vital signs would allow me to have an idea of how you’re doing in terms of, just on a basic level, your cardiovascular health.

All right. I’m a gastroenterologist. If I want to know the basics of what’s going on with you and your body, I need to know how you’re pooping and what your poop looks like, because 60% of it is microbial in origin, because it is not just the excrement of your food. What your poop looks like allows me to have insights into your gut health.

And we’ve actually proven this. We’ve actually proven this at Zoe, because what we found, we did a study called blue poo, and we fed people blue muffins. It had a blue food dye. And basically, it’s quite simple. You eat the muffins, and then you wait to see when they show up in the toilet bowl.

And based upon that time, which is basically your gut transit time, how long it takes for the blue dye to pass through your intestines, we could tell you what’s going on with your gut microbiome. We could talk about cardiovascular risk. We could talk about visceral fat, all quite simply tied to your gut transit time based upon eating a blue muffin.

So these things, many of these things that you and I are discussing today, whether it be the gut connecting to our metabolism, our immune system, or whatever it may be, we can connect them back to these simple measures, like what does your poop look like? Or how long does it take for you to have a bowel movement.

Understanding Gut Transit Time

STEVEN BARTLETT: The gut transit time. That’s super fascinating. I do want to talk about poop as well. But the gut transit time, that’s the time it takes from a muffin to go from my lips to the toilet bowl.

DR WILL BULSIEWICZ: Yes.

STEVEN BARTLETT: And is a high gut transit time better than a low one? And what is determining whether I have a high. A good gut transit time or a not so good one?

Gut Transit Time and the Blue Dye Test

DR WILL BULSIEWICZ: Yeah. So gut transit time is a personal measure of the health of this entire digestive system. The reason why you do the blue dye, by the way, instead of eating beets, or something like that is that the blue dye – we have clinically validated this. So this paper was published in the journal gut, which is the top European gastroenterology journal.

And there’s a couple specific time points that we can use to cut off these measures. The first is 14 hours. If you are less than 14 hours, that is very fast. The other is 58 hours. If you are more than 58 hours, that’s very slow.

All right, so you eat these muffins and then you basically just record when did they show up. And the average person is somewhere on the range of 24 hours or 48 hours, typically one or two days after eating the muffins. That’s when you start to see this. And those are both considered to be normal.

Now if we were to break these things out into less than 14 hours, more than 58 hours, or these two sort of peaks at 24 and 48, what you start to see is that this is four groups. And these four groups, every single one of them is a little bit different in terms of their gut microbiome, a little bit different in terms of their gut diversity.

We can make associations between these things and what people are eating. The high fiber consumers are all showing up in the middle, which means normal. And the low fiber consumers are the people that are showing up on the outside.

And it brings us to one of the properties of fiber that’s kind of fascinating, which is that whether you have diarrhea or constipation, there’s only one thing that can correct both of those. Diarrhea and constipation are both fixed with dietary fiber. It helps to normalize our stool, bring it back to the middle.

So in a perfect world, where do we want to be? We want to generally be pooping about once a day. So you want your gut transit time to be about 24 hours or less. That being said, is a person unhealthy if it takes two days for this to show up in their poo? No, I wouldn’t characterize them as being unhealthy. But I do think this is one of the things that we can look at that’s simple. It’s nearly free and available, all of us to try at home.

STEVEN BARTLETT: So yeah, so you would assert that if someone’s going to the toilets three or four times a day or more, then there’s probably a fiber problem. There’s may well be a fiber problem. And if they’re sort of chronically constipated, it’s also probably a fiber problem at the heart of it.

DR WILL BULSIEWICZ: Generally speaking, yes. Now I will say that fiber is not as simple as I wish that it was. And the reason why I bring that up is that for a person who’s low on their fiber consumption and they may suffer with these issues, increasing fiber is hard for them. And many people don’t feel well if they go too hard, too fast. When they do this, it folds them over. They feel unwell.

I was in the exact same spot 10 years ago. If I tried to eat chili with a bunch of beans, I was not happy. So I preferred to stay away from that.

So the point that I’m trying to make about this, the reason why people struggle with fiber is because we are 100% reliant on our gut microbes to digest our fiber for us. We don’t have the enzymes to break them down to break down fiber. The gut microbes are doing it.

So if you have a damaged microbiome and you never eat fiber, you can’t expect your microbes to be good at digesting fiber. Our microbes, they learn and they get good at the stuff that we allow them to practice. So when we start to add more fiber, the way that I recommend that people do this is to start low and go slow. That just means adding a little bit at a time slowly over the course of at least weeks, if not months. And this is what allows your gut microbes basically to keep up and adjust to what you’re doing.

Fecal Transplants: The Future of Gut Health

STEVEN BARTLETT: What about fecal treatment? You said there that if our gut microbiome is damaged, it’s not going to be great at processing the fiber. So can’t I just get someone’s poop who has, you know, that 60% of their poop is the microbes and eat it or do some kind of fecal treatment where I put it in my body?

DR WILL BULSIEWICZ: So this is actually being done now. We’ve been doing fecal transplants where we would take from a donor and put it into a person for an infection called C. Diff. And we’ve been doing this for more than 10 years. And it is fascinating.

The studies with fecal transplant in humans have not been as successful as they were for the C. Diff. So we would love to say that we could treat ulcerative colitis, which is inflammatory bowel disease, with a fecal transplant. Generally, it seems that we cannot, at least where we stand today.

But there is something interesting that we found in one of the studies on this topic, which is that there was one study where, again, these studies are small, we need bigger studies to really fully understand this. There was one study where they did have a couple of people with ulcerative colitis who went into remission, meaning that their disease was no longer active after a fecal transplant.

And they asked the question, what was unique? And they found they all had the same donor. So what we think is that there’s probably specific donors for specific diseases that could actually potentially fix those issues, because at their roots, they are gut issues.

I think that the future of fecal transplant is very promising, but the complexity of figuring out who are these donors? Could I be a good donor for some specific disease that I don’t even have myself and don’t know anything about? Possibly. And this is what we have to figure out.

STEVEN BARTLETT: And how do these poop transplants happen? Is it orally, or is it some other way? Are they injecting this poop? Are they putting it up their butt? What are they doing with it?

DR WILL BULSIEWICZ: There’s a couple ways. So the classic is a colonoscopy. So the way that I would always administer it is that the patient comes in for a colonoscopy. They’re completely asleep. They’re not aware of anything that’s happening. And during the procedure, I basically release this stuff. It’s a liquid, as gross as it sounds.

STEVEN BARTLETT: So that’s a tube up the butt.

DR WILL BULSIEWICZ: The colonoscopy? Yeah, that’s a tube up the butt.

STEVEN BARTLETT: Okay.

DR WILL BULSIEWICZ: Yeah, it’s tube up the butt. Now, the new technology that’s been emerging in the last few years is that they can actually dry out the stool, so they lyophilize it and put it into capsules. You have to take a ton of capsules in order to do this. But this is an alternative. Choice is, you could start taking this. What I think would be interesting breaks. Well, hopefully not.

STEVEN BARTLETT: Do you know what I mean? I’ve had a couple of Omega 3 capsules break, and it’s a nightmare.

DR WILL BULSIEWICZ: Oh, dear. Yeah. Imagine trying to get that show not where we want to be. What we’re transitioning towards – the past was this big event. You had to come in, get a big procedure, colonoscopy. Well, to do that repeatedly is simply not sustainable. That’s not realistic.

Now what we’re entering into is the possibility that you could do this every day. You could just take your poop capsule every single day.

STEVEN BARTLETT: God, I’d love to be the CEO of that company. That would be so fun.

The Great Microbial Extinction

DR WILL BULSIEWICZ: I mean, I think that this is going to happen. We just need really – yeah, but I think we need – the technology is there, the technology is there. So what do we need? We need to identify who are the proper donors for this, and we need to run the clinical trials to prove that it will work.

But to me, this is a super probiotic because it’s not just, you know, most probiotics are just one single strain, and they can be beneficial. I’m not disparaging probiotics in any way. They can definitely be beneficial. But what we’re talking about is a new future where you’re actually reconstituting a healthy microbiome.

And, Steven, on this topic real quick, it is fascinating because some of the people who are in this space, they’re worried about the way the world is going in terms of microbes, right? So there’s been this concept that perhaps you’ve heard about, which is that there’s been this great extinction event that’s taken place, right, where many species of animals are dying and they’re gone.

Microbial scientists are worried because the same thing is happening on a microbial level. So if you were to compare our microbiome as Westerners to a person who lives in a more primitive environment in Africa, we have half the microbes that they do.

And so what these scientists are doing is they’re saying, what if those microbes that you find in those people, what if we need them? What if we evolved and they’re required for us? So they’re creating a bank where they’re collecting these poop samples from primitive tribal people and saving them in the event that it turns out that the only way back is to actually take the poop from these people and create super probiotics that would help to reconstitute our microbiome.

The Economics of Poop

STEVEN BARTLETT: I’m so compelled by this idea that there’s going to be this range of supplements in the future that are just poop capsules.

DR WILL BULSIEWICZ: I don’t think it’ll be supplements, though. I think it’ll be completely regulated. Well, what I mean by that is there’s a difference in regulation between supplements and pharmaceuticals. And I don’t think they’ll have any choice but to regulate this on the same level that you would a drug.

STEVEN BARTLETT: Because in my head, I have this idea of, you know, if this really takes off, people with great poop are going to be, you know, expensive.

DR WILL BULSIEWICZ: Dude, I think my stock is rising, to be honest.

STEVEN BARTLETT: I want some of your poop.

DR WILL BULSIEWICZ: All right, if you want my poop, you will have to pay for it.

STEVEN BARTLETT: But it’s going to be expensive. If you only go to the – because you’re healthy, you go to the toilet once a day, it’s going to be gold.

DR WILL BULSIEWICZ: And that’s the fascinating thing. Poop is on the biggest comeback in the history of comebacks right now.

STEVEN BARTLETT: Maybe that’s where we live in a post AI world. Maybe that’s the currency we trade in, you know what I’m saying? Because we’re going to have little else to do.

DR WILL BULSIEWICZ: So I, you know, gosh, that is a dark, disturbing vision for the future. But I could see where that’s possible. I mean, I do think it’s fascinating to consider that what we once disparaged as completely worthless has turned into the powerful treatment that doctors are administering in the hospital to treat the uncurable infection. And now is the future of science.

STEVEN BARTLETT: It’s going to be so interesting. Could change the class system in the country? You know, upper class could just be people with the best poop and then lower classes. If you’ve got a really narrow gut microbiome and your poop is useless, you can’t sell it to anybody.

DR WILL BULSIEWICZ: Well, it’s kind of fascinating that you say that, because the issue is that if you look at the microbiomes of countries that are less developed than the U.S. and the U.K. you know, they have less money, which the result of this is that they eat a more basic diet, which often is based upon whole grains and legumes. Right? Beans and rice is the essential diet.

Yet these things are actually so good for our gut microbes. To me, legumes are the least talked about food that we should be talking about because they’re high in fiber, they’re high in resistant starches and polyphenols, all of which are prebiotics. And this is why when people eat more beans, they live longer with less disease.

So it’s kind of interesting. Cause proper food, cheap food is the food actually that is the best for us because it feeds these microbes.

STEVEN BARTLETT: Lazy Westerners are going to get on a boat they did once upon a time, the colonials, to go get the incredible, you know, the gold and the diamonds and whatever else it’s claimed that they stole from Africa. And they’re going to get back on that boat and go over there and start stealing poop.

DR WILL BULSIEWICZ: I think that I could definitely see that happening. There has actually been fights over when they discover prehistoric poop, fossilized poop, there’s fights over who gets to control that. Because if you think about – it’s Jurassic Park. Right? In the beginning of Jurassic park, there’s that amber with the mosquito, and the needle goes in. You extract the DNA. What if we could extract the DNA from prehistoric poop and study that and potentially use that?

STEVEN BARTLETT: The poop studies that have been done, really compelled by them. Because I hear that there’s been a lot of sort of poop transplant studies done in mice as well.

DR WILL BULSIEWICZ: Yeah.

STEVEN BARTLETT: And what are we seeing from those studies?

The Power of Microbiome Transfer Studies

DR WILL BULSIEWICZ: Okay. So we’ve talked about these different conditions that are connected back to our gut microbes. And part of the way that we prove this, of course we want human research, but part of building our argument and filling in the pieces of the puzzle is like mouse research. And these mice, we have complete control, and they’re much more simple to manipulate. And so we have the ability to do a fecal transplant, even potentially a human to a mouse, and then see what happens.

And so let me take you through a couple of examples of what we have seen in clinical studies, and I’m more than happy to point people towards the studies that I’m referring to. Classic study, they took identical human twins. So again, we were talking about this in the beginning of the episode. Identical human twins, same genetic code. And in this case, one was obese and one is thin, and they have a different microbiome.

And when you transfer human poop into mice, you also transfer the body type, even when you feed the mice the exact same food, the exact same number of calories. So we hear about this calories in, calories out concept, which, by the way, we could talk about if you want to, but it’s not perfectly true. And this is showing you the complexity that exists. Your microbiome impacts how you work with those calories.

The mouse that receives the obese microbiome, it’s like swimming against the current. The microbiome is making it basically so that that mouse absorbs all of those calories. And then the thin mouse, it’s like swimming with the current at your back. It’s a lot easier. You consume the same number of calories, you don’t gain any weight. That’s just metabolism.

By the way, we have studies also. Diabetes can be transferred. We have studies in humans where you can actually do a fecal transplant from a person who does not have diabetes to a person who does have diabetes, and their blood sugar measures will improve.

In humans, we have immune studies. You can take a person who has ulcerative colitis, which we were talking about a moment ago, and transfer their poop into a mouse, and that mouse will have ulcerative colitis. We have mood studies where you could take a human who has anxiety or depression or PTSD and transfer their poop into a mouse, and the mouse receives the mood phenotype.

So basically, this needs to be studied more. In humans, we are more complicated. You can’t just cure diseases by transferring poop among humans. Yet. But when it comes to mice where they are less complicated, it’s very clear that the microbiome plays a central role in these conditions, because you can transfer the condition using human poop.

How Microbiome Transfer Affects Metabolism

STEVEN BARTLETT: And take me on a journey of what that poop’s doing. So I get the skinny poop from a skinny twin, and I put it into a mouse. The mouse gets skinny, or I get the obese twin, I take the obese twins poop, and I put it into a mouse. The mouse gets obese. What’s going on in that mice’s body to make it obese? I’m assuming it’s basically picking up some of the microbes which are impacting the gut microbiome, which is creating a postbiotic compound which is influencing its metabolism or something. Something like that.

DR WILL BULSIEWICZ: You could eat the. So if you have a microbiome designed to produce short chain fatty acids, you and I could eat the exact same meal. But the person who has the microbiome designed to create short chain fatty acids will get more short chain fatty acids. And the product of this is that those short chain fatty acids now will have effects throughout the entire body, including affecting our metabolism, affecting our blood sugar, affecting our insulin sensitivity, affecting our blood lipids after a meal, affecting fat storage. Whether or not you turn on fat storage, or whether you turn off fat storage and turn on fat burning.

STEVEN BARTLETT: It really does shine a light on this calories in, calories out thing because. Yeah. I mean, there’s so many people, I’ve talked about this a few times that just think you just have to eat below the required amount of calories for your body and you’ll lose weight. But in that example, it proves that there’s this other process going on that’s going to determine, I guess, is it how many those calories go through, or is it just how your body processes that energy?

DR WILL BULSIEWICZ: Part of it is thermogenesis, meaning fat burning.

STEVEN BARTLETT: Yeah.

DR WILL BULSIEWICZ: Part of it is also what you poop out.

STEVEN BARTLETT: Okay.

DR WILL BULSIEWICZ: They’ve actually found that people who have a healthier microbiome, they poop out more calories.

The Problem with Calories In, Calories Out

STEVEN BARTLETT: Okay, interesting. What do you think of the calories and calories out there. If someone comes to you and they say, I want to lose weight, doc, and they say, I’ve heard this calories in, calories out thing is the answer. So I’m just eating less. I mean, lots of pizza, but I’m just having less calories.

DR WILL BULSIEWICZ: I don’t like that, obviously. So to me, dietary quality is the key. There’s too many examples where dietary quality. So first of all, our weight, our health is not entirely determined by our weight. Is it a major factor? Yes, it is, but there’s so much more.

So dietary quality, study after study after study shows us that dietary quality is crucial to the health of our microbiome and also to our global health, our longevity and our risk for disease. So to pretend that that doesn’t matter would be completely false and inaccurate. The idea that calories is the only thing that matters.

What I do want to say is this. There is some truth to the concept that calories matter. There’s absolutely some truth to this. If you reduce your caloric intake, you will lose weight. The problem is that your body will compensate by slowing down your metabolism. And so then it puts you in a predicament where you can’t continue to do this. It’s not sustainable because that weight loss eventually will stop and then your appetite signals will grow so much that you will start to overeat.

And then when you overeat, not only do you gain the weight back, you rebound. Yo, yo, you, yo, yo. And you go above where you were before.

STEVEN BARTLETT: Wow.

DR WILL BULSIEWICZ: And the problem with this is that when people lose weight, they don’t just burn fat, they lose muscle mass. All weight loss is associated with a loss of muscle mass. When you gain the weight back, the muscle doesn’t come back. You’re just getting fat. So the issue is you end up less healthy than when you started.

Natural GLP-1 Activation Through Diet

To me, what I want is I want people to eat a diet where they can eat as much as they want without restriction until they are full and still achieve their weight goals. And this is completely possible by consuming a diet that’s high in prebiotics.

Because we hear so much about Ozempic or Wegovy, which is semaglutide. We hear so much about this, and it’s a GLP-1 agonist. GLP-1 is a gut hormone that exists within our body and it makes us feel full. We can stimulate GLP-1 through our dietary choices. If you eat the right food, which is basically a high prebiotic diet, you will activate the GLP-1 and you will naturally feel full. And the result of this is that in the process of actually activating your normal satiety signals, you will consume less calories.

STEVEN BARTLETT: Satiety signals are basically hunger signals.

DR WILL BULSIEWICZ: Hunger signals. So basically, yeah. So the issue that we all have is that we eat an ultra processed diet. An ultra processed diet, number one, makes us ravenous, right. We can’t stop, we want it so bad. Number two, it doesn’t activate those fullness signals. And so the result is when we eat an ultra processed diet, we overeat. And then you feel terrible. You feel terrible for a couple of hours. And that is the result of you overeating. You’ve thrown yourself metabolically out of balance.

Don’t we all love the meal that tastes great, but you eat until you’re full and you stop and actually feel energized and don’t need to take a nap or drink an energy drink to compensate for what you just did. And that happens when we do this the old fashioned way. By old fashioned I mean prior to modern history when ultra processed foods came into existence.

If we go back to the old way of eating, you would simply eat until you activate these hormones, things like GLP-1, which you know is concentrated in this drug or peptide YY. These are gut hormones that basically tell our body when to stop eating.

The Ozempic Phenomenon

STEVEN BARTLETT: Everyone’s going crazy about Ozempic. I keep hearing about this drug. I think Elon Musk recently said he had had it. And I know a few other people that have started taking Ozempic there. I would say, you know, none of them are overweight necessarily.

DR WILL BULSIEWICZ: Yeah.

STEVEN BARTLETT: But they’re doing it because it’s now been framed as kind of super drug which can help you drop weight super quickly by making you feel satiated.

DR WILL BULSIEWICZ: Yeah.

STEVEN BARTLETT: What do you think of Ozempic?

DR WILL BULSIEWICZ: Well, I come back to this. So first of all, let me say that for people who need it, I’m glad it’s there. I don’t think that the entire world needs Ozempic in order to be healthy.

STEVEN BARTLETT: Is there any side effects or?

DR WILL BULSIEWICZ: 100%. 100%. First of all, digestive symptoms, Massive, massively common digestive symptoms. But there’s also long term risks and many of which we don’t simply know much about because people haven’t been using the drug long enough for us to really fully understand what happens if you use. Because once you start using it, you’re not going to stop. If you stop, you gain all the weight back. So once you start using it, you’re basically committing to however old you are, you’re going to be doing this for years on years, you know, decades. We don’t know what happens after a couple of years.

STEVEN BARTLETT: Isn’t it kind of skipping a step in the process of developing the gut microbiome? Taking Ozempic.

The Fiber Solution

DR WILL BULSIEWICZ: Yeah, I think that’s the point is that if we. So if we look at our countries, the US and the UK there’s a major fiber deficiency. And I don’t think, you know, I realize I’m out there pounding the drum on this, but I don’t think this is talked about enough. Perhaps because people don’t think the fiber is sexy, but I think fiber is sexy because it’s so crucial and important to our health. And this is an example where this is 100% true.

So 95% of Americans are deficient in fiber. The average woman is getting 15 grams of fiber per day. She’s supposed to be getting at least 25. In the US the average man is getting 18 grams of fiber per day. He’s supposed to be getting 38. That’s a massive, massive deficiency.

And the issue is that the fiber is what actually empowers the gut microbes, by the way, through short chain fatty acids. The fiber is what empowers the gut microbes through short chain fatty acids to release these gut hormones like GLP-1 and peptide YY.

So my thing is this because again, our health is not determined exclusively by our weight balance. There are other things other than that. Why don’t we try consuming these foods? The Average American is 10% of their calories from plants, fiber containing food. What if we can make that 30% or 50%? I think that we would see a massive difference.

There was a study that was done. It’s one of my favorite studies of all time by a professor in New Zealand. His name is Andrew Reynolds, and he compiled all of the available data on fiber. What happens when people consume more fiber? Here’s what happens. They lose weight. They are less likely to have a heart attack. They’re less likely to die of heart disease. They’re less likely to have a stroke. They’re less likely to be diagnosed with diabetes. They’re less likely to be diagnosed with multiple different types of cancer. They’re less likely to die of cancer. Their blood pressure goes down. Their blood sugar control improves, Their cholesterol goes down.

Okay, that’s sitting there for us available. All we have to do is make the dietary changes. And again, what happens in that process is you consume more fiber. It comes into contact with your gut microbes, they release short chain fatty acids and they have healing effects throughout your entire body.

So to me, I agree with you. I think that we’re missing this middle piece. And when we’re reaching for something that’s an expensive drug, it’s very expensive. When we’re reaching for something that’s an expensive drug and it has a very real risk of side effects. And it also has risk in the sense that we just don’t know what happens after you take it for a couple of years. I don’t understand why we would do that when think of the benefits that I just listed by simply increasing your fiber intake.

The Drug Culture Problem

STEVEN BARTLETT: I have so many conversations with my friends about various drugs that they’re taking, performance Drugs, Modafinil, Ozempic, etc. And when I speak to them, they. They’re very passionate that there’s no side effects on all of these sort of things that I consider cheating.

DR WILL BULSIEWICZ: Yeah.

STEVEN BARTLETT: And I. And I have to caveat this because there are some people who are in a situation with diabetes or other cardiovascular.

DR WILL BULSIEWICZ: Issues.

STEVEN BARTLETT: Who can have their lives saved with some of these drugs.

DR WILL BULSIEWICZ: Yeah.

The Cost of Taking Shortcuts

STEVEN BARTLETT: But for the most part, the people that I know that are consuming these drugs aren’t doing it for that reason. They’re doing it for vanity reasons or for performance reasons where it’s like taking a shortcut. And every shortcut I believe in life comes with a cost.

DR WILL BULSIEWICZ: Yeah, you’re talking like a doctor. You’re talking like a doctor because basically what you’re talking about is risk versus benefit. And the way that I think and every other doctor thinks about their patient is, does the benefit outweigh the risk? But there is always risk in association with these drugs.

And what makes me different from most other doctors where I turned the corner in my career is when I started to ask the question, why are we waiting until we get to the point that we need to write a prescription for a drug? Why are we waiting until that point? Why are we not intervening in a much earlier point where we could transform a person’s life and get them to a place where they never actually get this disease, or if they get this disease, it’s so much easier for us to control that.

And this is so. To me, what I come back to is basically what you’re getting at is, why would we take a drug if we could change our diet and our lifestyle and actually protect ourselves?

STEVEN BARTLETT: It’s easier. It’s easier. It’s much easier.

DR WILL BULSIEWICZ: Yeah, it is. It is much easier. There’s no doubt. But the problem is you pay a price for that.

STEVEN BARTLETT: And the price is unobvious. So you’ve got an easier option where the benefits are clear and the cost, the risk is unobvious. A logical human being would take that path if they can afford it.

Treating Symptoms vs. Root Causes

DR WILL BULSIEWICZ: I agree. The issue is that these are not the same things, though. And what I mean by that is that you have diabetes. Hypothetically, I hope you don’t. Hypothetically, you have diabetes. We give you a drug for your diabetes. That drug covers up the issue. I can get your blood sugar down, but that’s not fixing the problem. I’m not actually fixing your diabetes.

So to me, we shouldn’t equate taking a drug and controlling a disease on some level. But truly what we’re doing is we’re just putting a sheet over the problem so you don’t see it anymore. Does it result in better outcomes long term? Are you healthier as the result of controlling your diabetes with a drug? 100%, yes, no doubt.

But what if we could reverse your diabetes? Type 2 diabetes, which is the kind that people acquire as an adult, is highly reversible. Most people don’t realize that you don’t need to be drug dependent on diabetes drugs in order to fix this issue. Take them when you need them, but let’s work on the root cause. And by working on the root cause, we can actually reverse the true problem and get you back to a place where you don’t need the drug at all.

STEVEN BARTLETT: But doesn’t that require discipline and willpower and motivation?

DR WILL BULSIEWICZ: Well, I think it requires understanding the path forward and making choices that are sustainable and that make you excited. I would never ask a person to make choices that make them miserable. I’m asking people to make choices that make them feel great, make them feel energized, and yet at the same time, actually are contributing to better health so that they can live longer with less disease and be in a position that I want to be in, which is that I want to be in my 80s and still cutting a rug and dancing with my grandkids.

The Bristol Stool Scale: A Window Into Your Gut Health

STEVEN BARTLETT: So let’s close off on the subject of poop. My team actually prepared some poop samples earlier on because I was wondering, as a gastroenterologist, I wondered that if you could look at someone’s poop and determine whether they have good gut health and if you can understand what’s going on in their body just by how their poop looks. Because poop comes in many shapes and sizes. So what I have here is a variety of different shapes and sizes of poop.

For anyone that can’t see, look at the screen if you’re listening to this podcast on Spotify or YouTube. Different shapes and sizes of poop. This is real human poop, so I’m going to pass you that so you can play around with it.

And why does the shape and size of our poop tell us anything? Why does it matter? And how is it indicating something that’s pertinent to our overall health?

DR WILL BULSIEWICZ: Well, because it goes back to what you mentioned earlier, which is that 60% of the weight of our stool is actually microbial in origin. So if you want a window into your microbiome, look at your poop, you don’t necessarily need to go and do an expensive test. Quite simply, looking at your poop is one of the ways that you can tell what’s going on.

So there was a study that was done in the 90s, long time ago, and it was less than 2,000 people, exclusively in the city of Bristol, and it led to the creation of a chart called the Bristol Stool Scale.

STEVEN BARTLETT: I’ll put it on the screen.

The Big Poo Review: Largest Study on Bowel Movements

DR WILL BULSIEWICZ: And we’re going to run through this, but before we do, I want to mention a few things real quick. As the US Medical Director of Zoe, I’m proud of my contribution as a gastroenterologist, as a physician, to the work that we’re doing there. And we not only did the Blue Poo study, which we’ve talked about already, which is that you can eat your muffins and figure out your gut transit time, but we also did a couple of other things.

One is called the Blue Poo Challenge, where we had over 20,000 people across the planet who were basically eating blue muffins and then reporting back to us on what was going on with them and then more recently. So again, the Bristol study was 2,000 people, exclusively in the city of Bristol. We recently did the largest study across the entire UK on poop and what people were doing in terms of their bowel movements.

So it was called the Big Poo Review. And we had 142,000 people from across the UK basically fill out a 17 question survey. And part of what we were looking at was their Bristol stool form. We were also looking at how often they poop. By the way, the average person poops 1.7 times per day. And we were also looking at how it associates with different conditions. So as an example, one in five people in the UK are constipated. One in six people in the UK have diarrhea.

So it’s interesting to take a look at all these things. So now, getting into the Bristol stool chart, the dream.

STEVEN BARTLETT: That is real poop.

Breaking Down the Bristol Stool Scale

DR WILL BULSIEWICZ: This is lovely. This is the dream. This is where we all want to be. And this is a Bristol 4. The Bristol 4 is the classic where I come walking out of the bathroom in slow motion and rock music is jamming and doves are flying in slow motion, and I just am such a stud. And that’s after a Bristol 4. My wife knows what happens when I come out looking like that. It’s soft and formed. And it’s like a sausage or a torpedo, so pretty smooth.

Now, when we move from a four to a three, a three is not that big of a deal, but it is getting some cracks and crevices in it. And we’re moving towards constipation now a three. You know, a little more fiber, a little more hydration, some exercise. These are simple things that can help to get you back to a 4 if you’re having one of these.

But that moves us to a Bristol 2, where we are truly getting into constipation territory here. And basically, this is like if you took a whole bunch of marbles of poop and jammed them together so it still forms into something, but it looks like a pack of marbles of poop that are stuck together. So that’s a Bristol 2 stool. That’s constipation.

And then finally a Bristol 1 is when you’re having the rabbit pellets. And they’re hard, they’re not easy to get out. And sometimes they’re a lot bigger than this. These are small. So you would form this up into what would be like a golf ball. And that golf ball would be like a Bristol one. You form it up into a hard ball like this, but perhaps even bigger. And it’s actually hard for a person to pass this. It’s so big, it’s so hard that your bottom has a problem relaxing to let it out.

So Bristol 1 and 2 are forms of constipation. Let’s go back to the middle. And we’re going to start from five. The stool is soft. It’s not hard, it’s not lumpy, bumpy. It’s soft, but it’s starting to break into blobs. Different pieces of poop. So we’re moving towards diarrhea, where fragments of solid stool are a Bristol 6.

And then when it’s just like, or the other thing, a Bristol six could be like a cow pie, where there’s no form, it’s just someone plopped down this formless patty. And a Bristol 7 finally is straight liquid. Straight liquid.

What Your Poop Type Reveals About Your Health

STEVEN BARTLETT: And how is this pertinent to our gut microbiome, our health? What does this tell us about our health?

DR WILL BULSIEWICZ: There’s been now multiple studies, including our work at Zoe on the Blue Poop study that was published in the journal Gut. There’s now been multiple studies where basically what they found is that if you could look at which of these Bristol types you have, it does give us some insights into your gut microbiome and what’s happening there.

So now where do we want to be in a perfect world? We want to be somewhere on the spectrum of 3, 4 or 5. We ideally want to be a 4. You’re not unhealthy if you have a 3 or a 5.

STEVEN BARTLETT: So if this type 4 poop, which is kind of like a sausage, it’s kind of like a smooth sausage, is optimal. How does one do that? What is turning it into a type 4? What are they eating? Doing?

Diet’s Impact on Stool Quality

DR WILL BULSIEWICZ: Yeah, interesting question. One of the things that we found in the Big Poo review, which is our nationwide survey of 142,000 people, we actually looked at what they were eating and we were able to find associations between fiber intake and specifically plant based food intake and having a number four.

So in other words, we found associations between fiber intake and basically plant based food intake and having a number four. So basically what that means is the people that were having a number four bowel movement were consuming more legumes, whole grains, fruits and vegetables.

The people who were having, whether it be a type 1 or a type 7, they actually were quite similar in terms of their diet, which is that they actually were consuming lower amounts of fiber. Now the other thing to look at too is actually some studies have found that people who have more on the spectrum of constipation tend to have a higher fat diet, tend to typically consume more animal products, which of course are higher in fat.

And people that are more on the loose or diarrhea side of things tend to be consuming more plant based foods. So now you could have a very healthy diet and be having a Bristol 5. And that actually is not problematic. And the reason that you’re having the Bristol 5 is because you’re consuming so much fiber that actually you’re producing a lot of short chain fatty acids. And those short chain fatty acids, they’re like lubricants for your poop.

Gut Transit Time and Stool Types

STEVEN BARTLETT: And the gut transition time, how does that relate to these different types of poop? As you were saying that, I was thinking the 1 in 7, the type 1 and the type 7, the type 1 being those sort of hard nuts and the type 7 being basically diarrhea. I was assuming that those are the poop types that would happen with a lower and a super high gut transition type.

DR WILL BULSIEWICZ: That’s right. So a slow gut transit time, which is a gut transit time more than 58 hours. So again, and this is all with the blue muffins, you eat the blue muffin, it comes out 58 hours later, you are more likely to be having a Bristol one or Bristol two, which is the classic constipation form. There’s no way, no way that you would have slow gut transit time and have a Bristol 7. That’s not possible.

STEVEN BARTLETT: A diarrhea.

DR WILL BULSIEWICZ: Yeah, diarrhea.

STEVEN BARTLETT: So diarrhea comes out fast. And these sort of hard nuts, they take typically a long time.

DR WILL BULSIEWICZ: That’s right. And the reason why this is happening, you know, so when water moves through the intestines, because a ton of water moves through the intestines and one of the jobs that our colon has, the large intestine, is to pull the water out. So the more time that something spends inside the colon, the more it’s actually going to do that, pull the water out. This is the reason why when we have fast transit, it’s high in water. And this is also the reason why, when it’s slow transit, it’s extremely dry.

The Color of Your Poop: What It Reveals About Your Health

STEVEN BARTLETT: Okay, so that’s the shape and size of the poop. But what about colors of poop? I’ve got some different colours of poop here. I’ve got some red, some blues, some blacks, some greens, some whites and some yellows.

DR WILL BULSIEWICZ: Yes.

STEVEN BARTLETT: How is color pertinent to health and everything we’ve been discussing?

DR WILL BULSIEWICZ: All right, let’s break this down. So first of all, why is our poop brown? The answer to that question has to do with bile. Bile is produced by our liver. It’s actually involved heavily in digestion of fat.

So when we, for example, eat a fatty meal, our gallbladder will squeeze. People that have gallbladder issues know what I’m talking about. You eat a fatty meal, your gallbladder squeezes bile, then mixes in your intestines with the food, and the bile helps to absorb the fat. That bile is what makes our poop brown.

Now, that becomes particularly relevant if we’re talking about a white poop.

STEVEN BARTLETT: People poop white.

DR WILL BULSIEWICZ: Some people poop white.

STEVEN BARTLETT: No way.

DR WILL BULSIEWICZ: Yes. And the reason why a person would have a white poop is if there’s a blockage that stops the bile from mixing with their intestines.

On the flip side, if you are struggling to process your fat, you could have a yellow poop. And this could be a person who has, like, a pancreas issue, for example, chronic pancreatitis. And so if they’re not able to digest their fat, they have a fatty poop. It may come out yellow.

And one of the things that they’ll notice is that there may be an oil slick at the top of the toilet bowl.

STEVEN BARTLETT: Right.

DR WILL BULSIEWICZ: That’s fat. Oil is fat. So, all right, you’ve never had a. Have you ever had a green bowel movement?

STEVEN BARTLETT: None of your business.

DR WILL BULSIEWICZ: Answer the damn question.

STEVEN BARTLETT: No, I haven’t.

DR WILL BULSIEWICZ: Okay. I have.

STEVEN BARTLETT: Oh, really?

DR WILL BULSIEWICZ: Yeah. There’s a couple reasons. Some are healthy, some are not. So you could have diarrhea, like from an infectious cause. An example could be something called giardia, which is a parasite, and that’ll give you green poop.

But you could also go too hard on the smoothies. I was drinking, like, 40 ounces of green smoothies a day, and my poop would come out green. It was interesting.

We’re about to get into some that are really important. Before I do that, let me just mention real quick, the blue. So the blue poo. You could get a blue poo from eating blueberries, particularly if you eat a lot of them. Or alternatively, of course, this is the blue muffin, the blue poo challenge. And perhaps what we could do in the show notes is give people the recipe for how they can go about doing that if they’re interested.

Red and Black Stool: When to See a Doctor

All right, Red and black. So we have to talk about. Let’s start with red, because, of course, red. We think about blood. And I have a rule which is that if you see blood in your stool, that’s not normal. And to me, that’s grounds to talk to a doctor.

And, you know, then there’s different levels of intensity of how seriously we check it out. But, Steven, colon cancer, which can present with red stool. Colon cancer is the number two cause of cancer death in our countries. In the United States, 150,000 people are diagnosed per year. It’s highly preventable, and it’s shifting towards younger people.

There has been a change in the last few years in terms of colon cancer, where, you know, as an example, a person of your generation, you and I are pretty close, I think, but I’m a little bit older. A person of your generation is four times more likely to be diagnosed with rectal cancer during their lifetime than my parents were and twice times more likely to be diagnosed with colon cancer compared to my parents generation.

So there’s been this shift and it’s also affecting younger people. So my point is this. I’ve had patients who come to me, they go, “I saw a little bit of blood in my stool,” do a colonoscopy and discover that they have a massive polyp which is a precursor to cancer. And by removing the polyp, we just basically stopped them from developing cancer. So I take it seriously.

When you see a poop that is coated in red, all right, now that red may be just on parts of it like it is here where that’s typically bright red coming from the bottom. So that would be either something in your rectum, could be hemorrhoids, could be an anal fissure, could also be a polyp in the rectum.

But I think what I come back to is I would encourage people to get checked out because just seeing the bright red blood doesn’t mean it’s hemorrhoids. Don’t assume that. Right. Particularly with cancer shifting towards younger people. I think it’s important to get checked out.

STEVEN BARTLETT: On that point about cancer shifting towards younger people. Is that because our diets are changing?

DR WILL BULSIEWICZ: I think so. I think it’s the shift generationally that’s taken place in terms of our diets. I also think that there’s a microbiome element, the connections between the gut microbiome and colon cancer are as powerful as any type of cancer.

And at the same time, what protects us. And I think, you know what I’m going to say, it’s the fiber and the short chain fatty acids. And in that study that I was mentioning earlier from Andrew Reynolds, the professor from New Zealand, actually there was a powerful association between fiber consumption and protecting ourselves from colorectal cancer.

So powerful that for every 5 grams of fiber that we increase in our diet, we are getting a significant reduction in our risk. So it’s not just do you eat fiber or not? It’s actually how much fiber do you eat? And the more the better.

You know what I should mention real quick, red stool can also come from eating beets. It will almost always happen like literally of 24 to 48 hours after you eat the beets. So don’t be surprised when that’s the case. You may see a little bit of red stool.

Black stool can come from benign places. So an example is bismuth. So, like Pepto Bismol. So you have a stomach ache and then you take some Pepto Bismol. But the issue with this is it’ll actually give you black stool. So if you’re having a bad stomach for a couple days in a row, it could turn black.

But the other thing that turns your stool black that people need to know about is a slow GI bleed, bleeding into your stomach, specifically because that bleeding is happening higher up in your intestines. And then it has to pass all the way through, like, intestinal transit time. Right. Because there’s such a delay, by the time it gets down to your rectum, it’s now black. It’s not red anymore.

So black stool can be indicative of bleeding. The way that we can differentiate this is when it’s blood, it smells terrible.

STEVEN BARTLETT: Oh, now we got to start smelling our own poop.

DR WILL BULSIEWICZ: Yeah, well, you don’t have to stick your nose into it. It’s so clear. Like, it would be so clear. When I’m in the hospital, I will be walking through, and I can literally tell when a consult is coming because I can smell this diagnosis. Really? Yeah.

So anyway, the stool will turn black, it will smell terrible, and it will be like tar. That’s what makes it different than if you were to, for example, take Pepto Bismol.

How We Inherit Our Gut Microbiome

STEVEN BARTLETT: Right now, I’m really interested in this idea that we can give our gut microbiome to our kids, but also in the twin studies, they have such a diverse gut microbiome. So how much of our gut microbiome are we inheriting from our parents, our grandparents, et cetera, if any at all?

DR WILL BULSIEWICZ: Well, we’re certainly inheriting some, and particularly when we’re kids. As a newborn, you’re going to most closely resemble the gut microbiome of your mother. And that association and sharing is much more profound if you were born through a traditional vaginal delivery and if you’re breastfed.

So that connection between mom and baby actually helps to facilitate the transfer of microbes to the baby that leads to health. And this is part of the reason why when you disrupt these things, which, by the way, I should mention, sometimes these things are inevitable. So I have three kids. They were all born by cesarean. It’s not the way that we wanted it to be, but it’s what happened.

You can have healthy kids who are born by cesarean, but when we disrupt these things, whether it be cesarean section or bottle feeding instead of breastfeeding or antibiotics, we see downstream the same effects. Increased likelihood of obesity. Increased likelihood of allergic conditions, including food allergies and asthma. Increased likelihood of autoimmune conditions, including celiac disease and type 1 diabetes.

So when you disrupt the developing gut microbiome in that child, you increase the risk of these things happening subsequently. And there’s been some interesting studies where they will look at the microbiome, they’ll look in the diaper of a child who’s six months or a year old, and they can, based upon that, they can predict who within the next four to five years is going to develop an allergic or autoimmune condition.

The Power of Human Connection on Gut Health

So getting back to the sharing of microbes, yes, there is this connection between mom and child, but actually, this is an evolving thing throughout our life. And there’s new research that I think is really important about human connection.

And in this study, what they found is that people who shared spaces together through connection, they, number one, had a healthier gut microbiome than people who live by themselves. Number two, they share more microbes together. So, like, for example, me with my wife, we share more microbes together than I do with my siblings.

And then the other thing that was kind of fascinating from this study is the strength of the relationship matters. So I think we can all agree sometimes relationships are in a good place and sometimes they’re in a bad place. Right? And that’s like a whole spectrum and different conversation, but actually where it is on that spectrum impacts your gut microbiome.

They found that the couples that were sharing the most microbes were the ones that actually had the most connection in terms of their relationship, whereas the people who were disconnected from one another, they weren’t sharing so many microbes.

Now, you could say, like, is that because they’re having less sex, could it be that they just, like, physically aren’t even close to one another? I suppose that’s all possible, but these are also people where they controlled for their diet, so it’s not a dietary thing.

So I think that the takeaway from my perspective is the power of human connection is more important in 2023, 2024. It’s more important in this moment than it’s ever been. And many aspects of our life are pulling us away from this, our devices, social media. I mean, I’m very active on social media, but let’s be transparent about this. This is pulling us away from the ability to sit down with another person, look them in the eye, talk to them, have a meaningful conversation, and feel connected to that person. And because you feel connected, you reap the rewards, which do include better gut health.

STEVEN BARTLETT: But that’s super interesting because, yeah, it does make a case that the people we surround ourselves with, we tend to think of psychology, right? We tend to think that you surround yourself with a certain type of person. It’s good for your psychology if they’re positive or they’re negative, etc. But there’s actually a case that people, the people we surround ourselves with, have an impact on our physiology, our bodies, our biology, our gut microbiome, and that has an upstream effect on everything.

The Emotional Connection to Gut Health

DR WILL BULSIEWICZ: That’s true. But you also can’t disentangle or separate out from the fact that the positive influence of a person also really matters, because where you’re at from an emotional perspective, and I think this is an important thing for people to understand that where you’re at from an emotional perspective does manifest in your gut health.

And this is the reason why, for example, if a person’s going to go and do public speaking and they’re not comfortable with public speaking, they may just have a little bit of jitters, a little bit of nausea or queasiness, but it can also snowball into something bigger and worse, such as fold you over type cramps. So, and that’s many people will manifest their stress in their gut. That’s an acute example. By acute I mean this specific situation context that you’re involved with.

But what happens if your life is stress? And the answer to that question is actually very clear because people who, for example, have childhood trauma, they will subsequently go on and be far more likely to develop digestive issues, but other gut related issues.

And there was an interesting study, Steven, that was done among two year olds who were adopted, and they studied the gut microbiome of these kids and downstream they were able basically to identify that the fact that they came from an adopted home, even though it was before age 2, they can’t remember this, even though it was before age 2. The fact that they were from an adopted home, it affected their gut microbiome, it affected their response to stress, and it also affected the way that their brain works. And they actually were able to show this through functional MRI technology where they looked at the brain and how it…

STEVEN BARTLETT: Was activating just because of that sort of early trauma.

DR WILL BULSIEWICZ: Early trauma. So, and not everyone who has gut issues has been exposed to trauma. But I think it’s important for people to understand that if you have been exposed to trauma, this can be a very important part of your healing process. That’s the message that I want to get out into the world.

And the reason why I bring that message is because I’ve had people who are in my clinic and they’re like, “Dr. B, I do everything that you tell me to do, and I do it by the book. I eat, I sleep, I exercise, I do yoga and I meditate.” And despite that, they’re not getting better.

And in those relationships, what ends up happening is typically after a couple of visits, we start to get comfortable with one another, we trust one another. And when you get to that place, they will share with me something that happened to them. And then I make it clear this is the reason why when you heal the wound of the trauma, you actually heal the gut.

And it’s amazing because they’re like a rocket ship, because they’re doing all the right stuff, right? They’re eating right, sleeping right, exercising. And the minute you take away this thing that is chaining them down and holding them back, the minute you release those chains, they shoot to the moon. And it’s the greatest thing to see. And I would say that in my clinical career, that has been the most rewarding thing above anything else. Far more than getting a person to eat more fiber.

The Impact of Alcohol on Gut Health

STEVEN BARTLETT: What about alcohol? I’ve recently quit drinking alcohol.

DR WILL BULSIEWICZ: I’m glad you did.

STEVEN BARTLETT: Why are you glad I did?

DR WILL BULSIEWICZ: Well, let me be the first to say that I have not completely quit consuming alcohol. But if we remove my imperfect self from this picture and just look at the science, the science is actually quite clear. Our gut is damaged by alcohol.

So let’s take a step back for a moment. If I want to clean this table, right, we’re all done. We want to clean it up. What are we going to do? We pull out rubbing alcohol. It destroys microbes. Alcohol destroys microbes.

And when we drink to the point of having a hangover, is that dehydration? Absolutely not. And I’m of the belief, based upon the research that I’ve seen, that what’s happening when you’re having a hangover is that you have caused significant damage to your microbiome. And this is the reason why it takes 24 hours or more for you actually to start to feel like a human being again.

What you see with alcohol is disturbing. It’s more than just liver disease. There are many different health related conditions that are tied back to alcohol consumption. And the thresholds that we’ve set where we say, people, it’s okay, moderate alcohol, if you have up to three drinks a day as a guy or up to two drinks a day as a woman, that to me is ridiculous. That’s a lot.

But the study that changed everything for me was where they actually monitored levels of something called bacterial endotoxin or lipopolysaccharide. This is something that is not supposed to be in our bloodstream. When it is in our bloodstream, it’s because there’s been damage to the gut barrier and it causes inflammation. This is the exact same thing that can cause us to get extremely sick, but at a minimum, it is causing inflammation in your body.

And they did a study where they were basically monitoring levels of this lipopolysaccharide after alcohol consumption and in association with blood alcohol levels. And what they showed in the study is they were parallel lines. Blood alcohol level goes up. Lipopolysaccharide Level goes up, blood alcohol level turns down, lipopolysaccharide level turns down. They were the exact same thing.

So when I saw that, to me, even when we’re consuming minimal amounts of alcohol, we are potentially causing problems for our gut microbes.

The Brain-Gut Connection

STEVEN BARTLETT: What is the brain gut connection?

DR WILL BULSIEWICZ: So the brain gut connection is referring to the fact that your gut’s best friend is the brain. They’re talking to each other right now, and they are inseparable. You can’t get away from that.

There’s a number of ways that your gut will talk to the brain. So part of it is the release of neurotransmitters. 95% of the serotonin in your body is produced by the gut. Serotonin is the happy hormone. It’s what makes us feel energized. It’s what gives us great mood, and in some ways also gives us focus.

You would think that it comes from your brain. You know, when we treat a person with major depression, we treat them to increase serotonin levels. Yet only 5% of the serotonin in your body actually is produced inside your brain. 95% of it is produced within your gut.

Serotonin can signal the brain through a nerve called the vagus nerve. The vagus nerve is like a super phone between the brain and the gut. It would be like if you were in London and I were in the United States and I had a direct line to you where I just pick this up and I go, “Yo, Steven, I need to talk to you.” Right? That’s the way that this works. Your gut is talking to your brain directly on that phone line.

So serotonin, dopamine. 50% of dopamine, which is the reward hormone produced in the gut. There are over 30 neurotransmitters produced in the gut. There’s also the vagus nerve that we just talked about.

And then finally, your gut is producing metabolites, postbiotics, that can cross into the brain and have an effect. We mentioned this earlier. Short chain fatty acids from fiber have the ability to cross the blood brain barrier and actually influence things like our mood, our focus. There was one study with kids where by increasing short chain fatty acids for those kids, they actually were able to increase their focus because they were having trouble with focus.

Short Chain Fatty Acids: Nature’s Most Healing Nutrient

STEVEN BARTLETT: You’ve repeatedly talked about fiber and this thing you called short chain fatty acids in your book. You said you believe that they’re the most healing nutrient in all nature.

DR WILL BULSIEWICZ: I think that’s actually true. And I also would characterize them as the most anti inflammatory molecule that I’ve ever come across.

STEVEN BARTLETT: And am I right in thinking we eat fiber? The bacteria in our microbiome breaks down that fiber and it produces this thing, these short chain fatty acids.

DR WILL BULSIEWICZ: Right.

STEVEN BARTLETT: Is that it? That’s, that’s. I haven’t.

DR WILL BULSIEWICZ: But the story’s just getting started, though. Okay, yeah, the story’s just getting started because the issue is that. That’s the simple part, right? These magicians that live inside of us release these short chain fatty acids for…

STEVEN BARTLETT: Us by eating fiber.

DR WILL BULSIEWICZ: By eating fiber or resistant starches. Okay. But then those short chain fatty acids go to work, and our immune cells, our human cells, have receptors to receive these short chain fatty acids and act upon the information that they receive. So you could think of them as a signaling molecule in the sense that your gut microbiome is now talking to your body and telling your body what it wants your body to do.

STEVEN BARTLETT: So it’s training it.

DR WILL BULSIEWICZ: Yeah. But it has the ability to flip genes off and on. It has the ability to turn down your immune system. So as an example, when I think about autoimmune conditions, if we were to get super into the details of autoimmune conditions, what you would discover is that we need more short chain fatty acids to empower these specific cells, called T regulatory cells. And those T regulatory cells would actually turn down our immune system and protect us.

So, and it’s not to say that autoimmune diseases are exclusively the result of a fiber deficiency. There is certainly a genetic component, but there was a genetic component 200 years ago, 300 years ago, and yet these conditions really weren’t that much of a problem back then.

So many of these conditions didn’t have a name until the last 100 years. And the emergence of them, many of them, have increased 500% in the last 50 years. Why would that be? It clearly is not genetics. So it has to be related to our diet and lifestyle. And ultimately, when we talk about our diet and lifestyle, we’re talking about our microbiome.

Building Your Fiber Tolerance

STEVEN BARTLETT: And really, one of the most important places to start, as you say, is with the fiber, I think so. You said earlier on we have to start slow and low with fiber.

DR WILL BULSIEWICZ: Yeah.

STEVEN BARTLETT: And that’s because we’ve got to build up those microbes that respond to the fiber and turn it into the short chain fatty acids. Right.

DR WILL BULSIEWICZ: Your gut is like a muscle. Right. This is the way that I want people to understand this. Your gut is like a muscle. And a muscle is capable of work, but it has limitations. And the more that the muscle has been trained, the more capable of work it is.

So if you lift weights, you might start at 50 kilos. If we’re doing a bench press, you might start at 50 kilos, and then you go to 55 kilos, and then the 60 kilos, and you work your way up. And that’s the process of growing strong.

And your gut works the exact same way. So if you expose your gut to food, specifically a diverse mix of different foods, you are training your gut, and your gut will become more capable of consuming those foods over time. And then you can eventually get to a point where you don’t have to then restrict based upon your capabilities, because the capabilities are limitless. Now you can eat whatever you want.

Understanding Different Types of Fiber

STEVEN BARTLETT: And is all fiber the same?

DR WILL BULSIEWICZ: No, not all fiber is the same. Fiber is a very generic word. Fiber is like the word protein. No one would claim that the protein in a fish is the same as a protein in a bean, yet both of them contain protein. Fiber is unique to individual plants. There are many, many different forms of fiber, to the point that we don’t even know how many exist.

So what we know is this. It’s rather simple though, right? Given that despite that complexity, it’s rather simple. All plants contain fiber. Every single plant has unique forms of fiber.

We do split it into two major types. These are again, umbrella terms. These are big labels. Soluble and insoluble fiber. The soluble fiber is the kind that dissolves in a drink. It disappears. You don’t even know that it’s there yet. Typically, the soluble fiber is feeding the microbes. That’s the prebiotic fiber.

Insoluble fiber is the kind that’s the grit. So, if you were to add it to a drink, it’s not dissolving. It’s going to be there no matter what. You could boil the drink, there’ll still be fiber in it. So insoluble fiber most of the time is not the prebiotic fiber, but it does still serve a purpose. It helps in terms of your bowel transit, which affects your gut microbes. It helps in terms of your bowel movements, which affects your gut microbes. It helps in terms of other things, such as your cholesterol and your blood fat control.

So both types of fiber, both soluble and insoluble, have advantages. You don’t need to worry about those individually. You just need to know that you plants have fiber. Every single plant has a unique form of fiber. And every single plant will feed unique families of microbes as a result of this.

The F Goals Framework for Gut Health

STEVEN BARTLETT: You have these F goals you talk about in the book when you’re recommending diets that you think people should consider. And I think it’s important because this word diet is quite stigmatized, right? And it can lead to disordered eating and things like that. So I think it’s important for us to talk about that a little bit. But I do want to know what these F goals are. And when you use the word diet, you’re not saying something that’s unsustainable in order to have a short term.

DR WILL BULSIEWICZ: I’m saying actually the opposite. I want people to have abundance. In fact, if you were to ask me what is the biggest misconception that exists in the gut health space, my answer to that question would be that people are very quick to restrict and less quick to add back.

So with regard to F goals, this is my general framework. It is not the only thing, but this is my general framework for how I remember to organize my day in terms of foods that I’m trying to seek out. Each letter represents different categories of food.

So F fruit. I think fruit has been inappropriately villainized. I think fruit’s amazingly good for us. In fact, people that consume more fruit are less likely to have diabetes. They also lose weight.

Fermented. We’ve talked about fermented. You can add more diversity to your microbiome by adding fermented food. We need this.

G stands for greens. Greens have almost no calories, yet tons of nutrition. That’s good. And grains. By grains, I don’t mean refined grains. I mean unrefined grains. So whole grains. So good for us. Those are gut microbiome foods, high in fiber and resistant starches.

O stands for Omega 3 Superseeds. So that’s chia, flax, hemp, and also walnuts. Those contain omega 3 fats. Those are healthy fats that we need more of.

A stands for aromatics. So that’s onions, garlic, shallots. They’re delicious. They’re also great for your heart and protect you from cancer.

L is legumes. So legumes includes beans, peas and lentils. I would go back to saying, to me, this is the number one superfood because they’re gut health foods and they’re longevity foods. And if we look at the evidence with heart disease, cancer, stroke, diabetes, all across the board, you’re going to see these reduce your likelihood of having those diseases.

S When I got to S, I kind of lost my mind because I felt like I have more that I want to say, so let me just pack it all in. So S stands for shrooms, meaning mushrooms. Mushrooms technically are not plants, they’re fungi. But they contain fiber and are incredibly good for us. So they are honorary plants.

S also stands for seaweed. So most cultures don’t consume seaweed, but for example, in Japan, they do. And they’re incredibly healthy as a result of this. It’s another source of unique types of plants with unique sources of fiber.

And the last is, I’m going to. In the book, I said sulforaphane, which refers to a cancer fighting chemical that you will find in broccoli sprouts. But I want to rephrase this to say sprouts. So sprouts to me are superfoods. There’s something magical that happens.

What is a sprout, by the way? For people who are wondering, you could take any seed and if you quite simply add water, you will unlock nature because basically that seed is waiting to germinate and grow. So when you enter this code of basically unlocking it with water, it comes to life, it opens up and out shoots this plant. And that plant is the sprout.

And the sprout is tremendously high in fiber, protein, but also phytochemicals. There’s unique chemicals that you will find in these plants in a disproportionate level compared to. For example, I mentioned broccoli sprouts. Broccoli sprouts have 50 to 100 times more cancer fighting chemical than adult broccoli has. So eating a pinch of broccoli sprouts can provide just as much benefit as eating a head of broccoli.

Generational Loss of Microbial Diversity

STEVEN BARTLETT: So interesting. So if you’re a parent and you follow the F goals diet that you lay out in your book, the interesting thing I found is if you’re a mother and you’re having a child, you’re then going to pass on some of your microbiome to that child. And also I was reading about that mice study conducted that shows how the western diet induces a loss of microbial diversity that can compound over a series of generations.

DR WILL BULSIEWICZ: Yeah, that was a Justin Sonnenberg study. So Justin Sonnenberg is a guy that I’m a big fan of. He’s out in Stanford and he actually wrote a blurb on my first book, Fiber Fueled.

And so the issue is that we want to understand microbial loss that can occur over generations because clearly our generation is different than our grandparents. And it’s hard to do with humans because it takes us these days, 30 or more years to create a new generation. But with mice, you can do this very quickly.

So he basically started off with mice with a certain level of microbial diversity. The diversity of the microbiome is a measure of the health of their microbiome. And then he saw what happened with a low fiber diet.

Basically what he saw is that if you put them on a low fiber diet, that mouse will start to lose diversity and then it will transfer that onto its offspring, and then that offspring who’s still on a low fiber diet continues to lose diversity and transfer that onto their offspring and so on.

And what he found was that if during this process, you intervene and you add back the fiber, you can actually restore on some level the diversity within the microbiome. You can wake them back up, they can come back, but the issue is you won’t get all the way back to the starting point. So there is a certain level of loss that has taken place as a result of those choices that were occurring over generations.

STEVEN BARTLETT: If your grandmother has 1,200 species of microbes in her gut as a child, but by the time your mother was born, she had 900, that’s what your mother got then. If your mother loses 300 species in her microbiome, now you start off with 600, half of what your grandmother originally had.

DR WILL BULSIEWICZ: Right? And at some point the loss of those species becomes problematic because each of those species is there with a purpose. We evolved to have them, and when they’re absent, they’re not able to do their job. And the other microbes may not be able to step up to actually do what’s the job of what’s missing.

STEVEN BARTLETT: It’s just such a great case that, you know, keeping ourselves healthy is keeping our children healthy as well in many respects. And we also live with our children, so we’re creating an ecosystem in our homes of these microbes on everything.

DR WILL BULSIEWICZ: I think that’s completely true. And I also think that when we think about generational issues that exist, so you know, in many studies, they’ll say, if your parents had this, then you’re at risk for this. And we have assumed that these are genetic things. Yet much of the genetic research, much of which has been done by Tim Spector, my partner at Zoe, much of that has not played out to prove that it is in fact genetic.

I think what’s happening is not just the transfer of microbes. I think it’s also the transfer of lifestyle. And the lifestyle that gets transferred by generation is if it’s unhealthy. Then unfortunately, you’re transferring along the problems that come with that.

STEVEN BARTLETT: Interesting. So you’re transferring the lifestyle and the microbes which weren’t able to deal with the lifestyle that caused the disease.

DR WILL BULSIEWICZ: Right.

The Gut Microbiome and Sexual Health

STEVEN BARTLETT: So interesting. Sexual attraction is the last thing I want to talk to you about. Sexual attraction. In the gut microbe you mentioned earlier, sort of erectile dysfunction, there’s pheromones, there’s all of these sort of sexual components that lead us to having a great sex life. What is the link or the association between the gut microbiome and sex and good erections and desire and libido, if any at all?

DR WILL BULSIEWICZ: First of all, I think it’s quite clear that when people are sick, which of course they have a damaged gut microbiome, when people are sick, the libido is gone. Right. That’s a part of that territory.

Libido is also associated with hormones, and there’s a number of different hormones that our gut microbes have the ability to impact for women, estrogen. There’s a term that’s called the estrobolome. And estrobolome sounds a little bit like microbiome because basically what we’re referring to are the microbes that control estrogen levels in women.

STEVEN BARTLETT: So the gut microbiome creates estrogen, it.

DR WILL BULSIEWICZ: Controls the recirculation of estrogen.

STEVEN BARTLETT: Okay.

DR WILL BULSIEWICZ: So estrogen has this circular pattern, and in that circular pattern it can basically be pooped out or it can enter back into the system. And the gut microbes are the gatekeepers. So they have the ability to actually control estrogen levels in the body on a certain level.

This is the reason why, if you look at estrogen driven conditions, breast cancer, ovarian cancer, endometrial cancer, endometriosis, what you discover is that in these conditions there’s damage to the gut microbiome in all cases. So. And it provides the suggestion, not yet proven, it provides the suggestion that damage to the microbiome may be fueling alteration of this estrogen level.

All right. The same is also true with testosterone or androgens, male sex hormones, which by the way, of course, all men have estrogen and all women have male sex hormones as well. It goes both ways. It’s just the dominance between the two genders.

So there’s a bacteria called Clostridium sindens that’s been known to basically affect male testosterone levels. And there are conditions, for example, polycystic ovary syndrome in women, that it’s the imbalance between the estrogen and the androgens, that’s strongly associated with the manifestation of this condition, polycystic ovary syndrome. And we suspect that the gut is central to this.

Okay, so first of all, the first point is that hormonal related issues are connected back to our gut microbes. All right? So libido, sex, these things obviously have a hormonal element to them. And this is the reason why erectile dysfunction, or I’m quite sure not as well studied because it’s not as easy to provide a diagnostic label to this. But female sexual desire, I’m quite sure would also be associated with the gut microbiome. I’m almost positive of this.

The question that I come back to, that I find to be very interesting is that the role, is the role that the microbes play in matchmaking.

STEVEN BARTLETT: Between two human beings. Between two human beings making me attracted to another human.

DR WILL BULSIEWICZ: Yes. So, and I come back to basic questions. So now look, I’ve been married for 10 years, so it’s been a long time since I’ve been a single guy. But I think we can all relate to, you’ve been on a date and there was something, not personality, there was something about the person, perhaps the smell that you noticed that you’re just like, “this is a turn off, this is not going to work.” Right. Or it could be in the way that a person kisses.

And these compatibility issues, I am convinced, actually come from the gut microbiome, that they are, in a way, matchmakers and that we’re looking for good partners. I can’t put my finger on exactly what that means, what makes a good partnership. But we do know that that partnership we discussed earlier ultimately has an effect on your gut microbiome because you’re going to share.

I am convinced that sexual attraction is brought back to these things. And in animal studies, it’s harder to do in humans. But in animal studies they have actually discovered that the pheromone levels, how you smell, your sort of attractiveness hormone is connected back to the gut microbes.

So kissing is connected to the gut microbes. Pheromones are connected to the gut microbes. Sexual desire and libido and male erection are connected to the gut microbes. I don’t know where the line exists, where it would stop. I think it’s all connected.

STEVEN BARTLETT: Okay, so if I want to be more attractive, do I just need to eat some sprouts? What are you saying here? Because is it about compatibility or is it about gut health?

DR WILL BULSIEWICZ: I think that it’s very clear. So attraction is a complex thing. Of course, we all have a different take. You know, I mean, I have friends who. There’s someone that they find attractive and it’s completely different for me. Right. And that’s all good. I’m glad that we have a different take because variety is necessary in terms of the genetic pool. Right. We need everyone, different people to want different things.

That being said, I kind of feel like there are certain innate qualities in a person that we would universally agree are attractive. And those tend to be measures of health.

STEVEN BARTLETT: We usually think. Yeah, you’re right.

DR WILL BULSIEWICZ: Yeah.

STEVEN BARTLETT: Because I was going to say we think of them as physical things, right. Things we can see with our eyes, typically, or things we can consume with maybe our ears, you know, jokes or humor or wit or personality or whatever. But it’s completely plausible that there is invisible things.

The Connection Between Inner and Outer Health

DR WILL BULSIEWICZ: Well, I don’t think that the visible things can be disconnected from the invisible things. And that’s one of the messages from the show today, is that even the way that you look, the radiance of your skin, your youthful appearance, your body shape, and there’s many forms of body shapes that are attractive. I mean, I’m not saying that there’s only one, but these are manifestations of what’s happening on the inside.

Introducing 38 Terra: Daily Microbiome Nutrition

STEVEN BARTLETT: Would you recommend supplements? I know you’ve produced your own supplement, which I have here, and I’ve actually been drinking, as we’ve been talking, called 38 Terra.

DR WILL BULSIEWICZ: Is it 38 Terra? And 38 Terra, what that means is 38 trillion. So this is in reference to the 38 trillion microbes that live inside of us. And this particular product is called Daily Microbiome Nutrition.

So in this product we are using specific ingredients at specific doses that have been clinically proven to have an effect and to have a benefit for your body. That includes things like improving your gut microbiome. It also means improving your bowel movements. We talked about going from a Bristol 1 or 2 or a Bristol 6 or 7 back to a Bristol 4. That’s what I’m talking about right now.

But also reducing digestive symptoms. So these are the benefits that we would get from regular use of a prebiotic. It’s easy, it’s a powder. You’ve been drinking it. I think it tastes pretty good. I don’t know what you think.

STEVEN BARTLETT: I was shocked and it was so delicious.

DR WILL BULSIEWICZ: Yeah, refreshing.

STEVEN BARTLETT: I’ve actually finished it all. I had it. We started the interview with it in this bottle here. And it’s all gone. Where do people find this 38 Terra?

DR WILL BULSIEWICZ: 38 Terra is available at our website. So you come to 38terra38terra.com and we are launching in mid January for the first time. We’re launching in the US and Australia. So in the UK it may be more difficult to get access to. But just be aware that if there’s enough of a demand, then we would serve that demand.

STEVEN BARTLETT: But if I am in the UK, I can still order it. There would just be probably shipping costs instead of. That would just be the shipping costs. Okay, super interesting. I’ve learned so much today, and it’s crazy because I didn’t think I had much else to learn about the gut microbiome. We had lots of conversations about it, but it’s really, it’s inspired me, it’s informed me, and it’s given me a sort of actionable blueprint to start taking action in my life.

Key Takeaways for Gut Health

DR WILL BULSIEWICZ: And if I were just to close that out, you know, what are the takeaway messages for everyone? Eat a wide variety of plants, fruits, vegetables, whole grains, seeds, nuts, legumes. Every single one of these counts. Coffee counts. Great. Absolutely.

So add more variety to your diet. Add fermented food to your diet. Get outside and exercise. Get a good night’s rest. Hug that person that you care about. Focus on human connection. Like these, to me, are where the priorities are at. Many of these things, by the way, are completely free.

The Closing Question: When Have You Been Happiest?

STEVEN BARTLETT: We have a closing tradition on this podcast where the last guest leaves a question, not knowing who they’re going to be leaving it for. And the question that has been left for you, when have you been happiest in your life? You may define happy in any way you like.

DR WILL BULSIEWICZ: Happiness is, I think, what really matters. And I think we have a problem in today’s world of excessively fixating on the objective things like money and losing track of the things that are less measurable. I have no clue how happy you are at home. I have no clue. Right. I have an idea of where you’re at financially. Yet. This is where the essence of life is.

And to me, my happiness comes from my family. It’s the side of me that you wouldn’t know unless you, like, literally were my friend in Charleston, South Carolina, and spending time with me, the real person, right? But regardless of what you see on this camera or hear on this episode, we are real people with real lives. And to me, my happiness comes from the pursuit of things, with my family doing everything within my power to fight for them. And also just to enjoy time with them. That’s what it’s about.

Final Thoughts and Gratitude

STEVEN BARTLETT: That’s a beautiful answer. Thank you so much. Dr. Will, you have a remarkable ability to communicate, but also you have a wealth of knowledge that is unrivaled as it relates to the issues we’re talking about today. And it’s really, really incredible. You’re really, really incredible and you’re doing so much fantastic work for so many people.

Because it wasn’t until a couple of years ago that I learned about the gut and microbiome. And I know because I can see the data that the society at large are on a journey of now understanding the gut more and more. And the research that’s coming out every year is pushing us closer to that understanding. And that understanding will unlock the things that we’re all aiming for in our lives, which culminate in what you said there, which is happiness.

So that’s the work you’re doing, you’re increasing public happiness. And I think that’s something that’s an incredibly worthy mission. So I thank you for that. On behalf of all the people that are listening today that got to this part in the conversation and that don’t have a means of reaching you directly, thank you. On behalf of all of us, thank you.

Where to Find Dr. Will Bulsiewicz

DR WILL BULSIEWICZ: It’s, I’m honored to come on the show with you. And for people who want to continue that conversation, this is why I put things out into the world. And you can find me on social media as the gut healthMD, Instagram, Facebook, I am on TikTok, but I think a 14 year old stole my handle. So the gut healthMD underscore is how you’ll find me there.

But also you can come to my website, ThePlantFedGut.com Sign up for my free email newsletter. That’s how I communicate, like I think the most effectively. Like I break down studies there. So come sign up for my email newsletter and if you want to check out 38 Terra, you can learn more there as well.

STEVEN BARTLETT: I’m going to put everything in the show notes. I’m also going to put in the show notes, which is the first time I’ve ever done this. I’m going to put the brief for this conversation in the show notes and what the brief is, it’s essentially all of the research my team did and they condense it down into about 10 pages.

And I think that’s really important because we’ve covered so much ground here today that someone just listening, someone who was having like a second screen experience or was doing the dishes or on the tube or whatever. There’s a lot there. The 10 pages you’ll find in the show notes summarize this conversation, the key takeaways and the actionable insights. And this is something I’m actually going to start doing on an ongoing basis.

Also, the materials we discuss in this conversation, like the Bristol Stool Chart and all of the other information that you talked about, which we’ll pull from you after this conversation, will be in the Show Notes, including links to find Dr. Will everywhere on social media and on his website.

DR WILL BULSIEWICZ: Amazing. That sounds so cool. Can’t wait to check that out.

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