Dr. Michael Greger on Food as Medicine: Preventing and Treating The Most Common Diseases with Diet (Transcript)
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Dr. Michael Greger
Good evening. For those of you unfamiliar with my work, every year I read through every issue of every English-language nutrition journal in the world so you don’t have to. Every year, my talks are brand new, because every year the science is brand new.
I then compile all the most interesting, the most groundbreaking, the most practical findings to new videos and articles I upload every day, to my nonprofit site, NutritionFacts.org.
Everything on the website is free. There’s no ads, no corporate sponsorships; it’s strictly noncommercial, not selling anything. I just put it up as a public service, as a labor of love. New videos and articles every day, on the latest in evidence-based nutrition.
In my 2012 review, I explored the role diet may play in preventing, treating, and reversing our deadliest diseases. In 2013, I covered our most common conditions. And, in 2014, I went through our leading causes of disability. This year, I’d like to address some of our most dreaded diseases, and cancer tops the list in the latest Gallup Poll.
The number one cancer killer in the United States, of both men and women, is lung cancer. But, if you look at the rates of lung cancer around the world, they vary by a factor of ten. If there’s nothing we could do to prevent lung cancer, you’d assume the rates would be about the same everywhere, just having kind of randomly. But since there’s a huge variation in rates, you assume there’s some contributing cause. And indeed, we now know smoking is responsible for 90% of lung cancer cases. So, if you don’t want to die of the #1 cancer killer, by just not smoking, you can take 90% of your risk and throw it out the window.
Colorectal cancer is our second leading cause of cancer death, and for that there’s an even bigger spread around the world. So, it appears colon cancer doesn’t just happen; something makes it happen. Well, if our lungs can get filled with carcinogens from smoke, maybe our colons are getting filled with carcinogens from food. Why do African Americans get more colon cancer than native Africans? Why that population? Because colon cancer is extremely rare in native African populations; like more than 50 times lower rates than Americans, white or black.
We used to think it was all the fiber that they were eating, however, the modern African diet is highly processed, low in fiber, and yet there has been no dramatic increase in colon cancer rates. And we’re not just talking low fiber intake, we’re talking United States of America-low fiber intake, down around half the recommended daily allowance. Yet, colon disease remains rare in Africa, still 50 times less colon cancer.
Maybe it’s because they’re thinner and exercise more? No, they’re not, and no, they don’t. If anything, their physical activity levels may actually be lower than ours. So, if they’re sedentary like us, eating mostly refined carbs, few whole plant foods, little fiber, like us, why do they have 50 times less colon cancer? Well, there is one big difference. The diet of both African Americans and Caucasian Americans is rich in meat, whereas the native Africans’ diet is so low in meat and saturated fat, they have cholesterol levels averaging 139, compared to over 200 in the U.S.
So yes, they don’t eat a lot of fiber anymore, but they continue to minimize meat and animal fat intake, supporting evidence that perhaps the most powerful determinants of colon cancer risk are the levels of meat and animal fat intake. So, why do Americans get more colon cancer than Africans? Maybe, the rarity of colon cancer in Africans is associated with their low animal product consumption.
But why? Did you ever see that take-off of the industry slogan, “Beef: It’s What’s For Dinner” – “Beef, It’s What’s Rotting in Your Colon”? I remember seeing that on a shirt with some friends, and I was such the party pooper, no pun intended — explaining that meat is fully digested in the small intestine, and never makes it down into the colon. It’s no fun hanging out with biology geeks but, it turns out, I was wrong.
It turns out, up to 12 grams a day of protein can escape digestion, and when it does, it reaches the colon, it can be turned into toxic substances, like ammonia. This degradation of undigested protein in the colon is called putrefaction; so, a little meat can actually end up putrefying in our colon. The problem is some of the by-products of this putrefaction process can be toxic.
The same thing happens with other animal proteins. If you eat egg whites, for example, some of that can putrefy, too. But, there’s protein in plants as well. The difference is that animal proteins tend to contain more sulfur-containing amino acids like methionine which is found concentrated in fish and chicken, and then eggs, less in beef and dairy, and much less in plant foods, which can be turned into hydrogen sulfide in the colon, the rotten egg gas that, beyond the smell, that can produce changes in the colon that increase cancer risk.
Now, there is a divergence of opinion as to whether it’s the animal fat, cholesterol, or animal protein that’s most responsible for the increased cancer risk, as all three has been shown to have carcinogenic properties. But, does it really matter since a diet rich in one is high in the others.
But the protein does more than just putrefy, though. Animal protein consumption causes an increase in blood levels of a cancer-promoting growth hormone called IGF-1. But, remove meat, egg whites, and dairy proteins from our diet, and our bloodstream can suppress cancer cell growth about eight times better. An effect so powerful, that Dr. Ornish and colleagues appeared to able to reverse the progression of prostate cancer without chemo, without surgery, without radiation; just a plant-based diet and other healthy lifestyle changes.
The link between animal protein and IGF-1 may help explain why those eating low-carb diets tend to die sooner, but not just any low-carb diet — specifically those based on animal sources, whereas, vegetable based low-carb diets are associated with a lower risk of death. But, meat based low-carb diets are high in animal fat as well; so, how do we know it wasn’t the saturated fat and cholesterol that was killing people off and had nothing to do with the animal protein?
What we would need is a study that follows a few thousand people and their protein intake for 20 years or so, and see what happens, who gets cancer, who doesn’t, who lives longer. But, there has never been a study like that…until now.
6,000 men and women over age 50, across the U.S, followed for 18 years, and those under age 65 with high protein intake had a 75% increase in overall mortality and a 4-fold increase in dying from cancer. But, not all proteins. Specifically, animal proteins, which makes sense given the higher IGF-1 levels in those eating excess protein. Eating animal protein increases IGF-1 levels, which increases cancer risk.