Friday Favorites: The Best Dietary Changes for Colon Cancer Prevention

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

What happens to the health of our colon within just two weeks after switching from standard American diet to one centered around plants? Watch the video to find out.

We have “100 trillion micro-organisms” residing in our gut, give or take a few trillion, but “the spread of the Western lifestyle has been accompanied by microbial changes,” which may be contributing to our epidemics of chronic disease. The problem is that we’re eating these meat-sweet diets, characterized by “a high intake of animal products and sugars, [processed foods], and a low intake of [whole plant foods].”

Contrary to the fermentation of the carbohydrates that make it down to our colon—the fiber and resistant starch that benefit us “through the generation of [these magical] short-chain fatty acids” like butyrate—”microbial protein fermentation [when excess protein is consumed…that] generates potentially toxic and pro-carcinogenic metabolites involved in [colorectal cancer].” And so, what we eat can cause an imbalance in our gut microbiome, and potentially create “a ‘recipe’ for colorectal cancer,” where a high-fat, high-meat, high-processed food diet tips the scale towards dysbiosis and colorectal cancer, whereas a high-fiber and -starch, lower-meat diet can pull you back into symbiosis with your friendly flora, and away from cancer.

We now have evidence from interventional studies suggesting that “adopting a plant-based, minimally processed high-fiber diet may rapidly reverse the effects of meat-based diets on the gut microbiome.” So, what may be “a new form of personalised…microbiome…medicine for chronic disease”? It’s called food, which can “rapidly and reproducibly alter…the human gut microbiome.” Switch people between a whole food plant-based diet and more of an animal food-based diet, and you can see dramatic shifts within two days, which can result in toxic metabolites. Switch people to an animal food-based diet, and levels of deoxycholic acid go up, which is “a secondary bile acid known to promote DNA damage” and liver cancers. Why do levels go up? Because the bad bacteria producing the stuff triple—in just two days.

And, over time, the richness of the microbial diversity in our gut is disappearing. Here’s our bacterial tree of life that’s getting depleted. Why is this happening? The “fiber gap.” “A low-fiber diet is a key driver of microbiome depletion.” Yeah, there’s antibiotics, and Caesarean sections, and indoor plumbing, but “the only factor that has been empirically demonstrated to be important is a diet low in…MACs’ (not Big Macs), “microbiota-accessible carbohydrates,” which is just a fancy name for fiber found in a whole plant foods and resistant starch, found mostly in beans, peas, lentils, and whole grains.

Our “intake of dietary fiber,” our intake of whole plant foods, “is negligibly low in the Western world” when compared to what we evolved to eat over millions of years. “Such a low-fiber diet provides insufficient nutrients for [our] gut microbes, leading not only to the loss of [bacterial diversity and richness], but also to a reduction in the production of [those beneficial] fermentation end products…” that they make with the fiber. We are, in effect, “starving our microbial self.”

What are we going to do about “the deleterious consequences of a diet deficient in” whole plant foods? Create new-fangled “functional foods,” of course, and supplements, and drugs—prebiotics, probiotics, synbiotics. Think how much money there is to be made! Or, we could just eat the way our bodies were meant to eat. What kind of value is that going to get your stockholders, though? Don’t you know probiotic pills may be “the next big source” of Big Pharma billions?

Why eat healthy though, when you can just have someone else eat healthy for you, and then get a fecal transplant from a vegan! Researchers compared the microbiomes of vegans versus omnivores, and found the vegan’s friendly flora were churning out more of the good stuff, showing that a plant-based diet may result in more beneficial metabolites in the bloodstream and less of the bad stuff like TMAO. But while the impact of a vegan diet on what the bacteria were making was “large,” the “effect on the composition of the gut microbiome [was] surprisingly modest.” They “only [found] slight differences between the gut microbiomes of omnivores [versus] vegans”? That was a shocker to the researchers; this “very modest difference…juxtaposed against the significantly enhanced dietary consumption of fermentable plant-based foods.” The vegans were eating nearly twice the fiber. Anyone see the problem here? The vegans just barely made the minimum daily intake of fiber. Why? Because Oreos are vegan, Cocoa Pebbles are vegan, french fries, Coke, potato chips; there are vegan Doritos and Pop-Tarts. You can eat a terrible vegan diet.

Burkitt showed that you need to get at least 50 grams a day (of fiber) for colon cancer prevention. And that’s only half of what our bodies were designed to get. We evolved getting about 100 grams a day. And that’s what you see in modern populations that are immune to epidemic colorectal cancer. So, what if instead of feeding people a vegan diet, you just fed people that kind of diet, a diet centered around whole plant foods? We’ll find out, next.

Colon cancer is our second leading cancer killer, but some places, like rural Africa, have more than 10 times lower rates than we do. The reason we know it’s not genetic is that “[m]igrant studies, such as those in Japanese Hawaiians, have demonstrated that it only takes one generation for the immigrant population to assume the colon cancer incidence of the host Western population.” Now, “the change in diet is [considered] most probably responsible for this.” But there are all sorts of changes when you move from one culture to another—like smoking rates, different exposures to chemicals, infections, antibiotics. You don’t know if it’s the diet…until you put it to the test.

It’s rare I do a whole video on a single study, but I think you’ll agree this one is worth it. This international group of researchers were trying to find out why colon cancer rates were an order of magnitude higher here—in African-Americans and Caucasians—than in rural Africa. If you look at American colons, they’re a mess: polyps, diverticulosis—not to mention hemorrhoids— whereas the African colons were “remarkably pristine.” And more importantly, sevenfold lower colonic epithelial proliferation rates, a characteristic of precancerous conditions. They measured everything they were eating, and concluded that the higher colorectal cancer risk and proliferation rates were most closely “associated with higher dietary intakes of animal products,” which may have led to “higher colonic populations of these potentially toxic [acid] and bile-salt-producing bacteria.” But you don’t know… until you put it to the test. “The higher rates are associated with higher animal protein and animal fat, and lower fibre consumption,” more of those bad bile acids, less of those good short chain fatty acids like butyrate, and that “higher mucosal proliferation. But how do we know it’s the diet that’s mucking things up? You don’t know…until you perform an interventional study.

How about we just swap their diets? Feed the Americans a high-fiber African-style diet, and the poor Africans get the SAD, Standard American Diet—like sausage and white flour pancakes for breakfast, a burger and fries for lunch, and some meatloaf and white rice for supper. That was day one for the rural Africans in the experiment, whereas the Americans were forced to eat fruits and vegetables, corn and beans. To help with compliance, they threw in more familiar foods like veggie dogs, though note it was not a vegan diet, just generally plant-based.

And the food exchanges weren’t for years, but just two weeks. Could they see changes that fast? The dietary changes “resulted in remarkable reciprocal changes” in the lining of their colons in terms of cancer risk and their microbiome. Switching to plant-based boosted the fiber fermentation and “suppressed the [carcinogenic] bile acid synthesis.” Let’s look at some before-and-after pictures. They took biopsies, and this is the colon lining of an African-American under a microscope. Those brown dots mark dividing cells; their colon lining was in overdrive, the cells rapidly dividing, a sign of premalignancy, a risk factor for cancer. But just two weeks eating a healthier diet, and their colons calmed right down.

The African-Africans started out with some proliferation, but it got worse on the American diet. This is a different marker measuring inflammation. Each of the brown dots here represents an inflammatory cell; so, rife inflammation before calmed way down after just two weeks, and the opposite in those eating worse.

We know that when our friendly flora ferment fiber, they produce beneficial compounds like butyrate, which is anti-inflammatory and anti-cancer. Impressively, “Africanization” of the diet more than doubled butyrate production, whereas “westernization” cut it in half. And in terms of toxic metabolites, a significant drop on the healthier diet, whereas the meatloafy diet increased the levels of these carcinogens by 400 percent within just two weeks. So, bottom line (no pun intended): what they were able to show is that just by changing the food, you can remarkably change your risk. In fact, that’s how the lead investigator put it: “change your diet, change your cancer risk!” It may be “never too late to start” eating healthier.

Based on these kind of data, “adopting a whole-food vegan or [even just] near-vegan diet rich in fruits and vegetables,” along with other healthy lifestyle decisions, “could have a stunningly positive impact on the cancer risks not only of black Americans, but of all peoples.” “While it [might] be unrealistic to expect rapid and profound lifestyle changes in the general population, [hey]…at least we have sound, effective advice to offer to those who [make the choice] to take the steps needed to optimize their healthful longevity.”

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Image credit: Kristina DeMuth. Image has been modified.

Motion graphics by Avocado Video