 We have 100 trillion microorganisms 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 resistance starts to benefit us through the generation of those magical short-chain fatty acids like butyrate, microbial protein fermentation. When excess protein is consumed, that generates potentially toxic and procarcinogenic 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-need, 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 might be a new form of personalized 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 this 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 in caesarean sections and indoor plumbing, but the only factor that has been empirically demonstrated to be important is a diet low in max, not big max, microbiota-accessible carbohydrates. It was just a fancy name for fiber found in 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 the 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, symbiotics. Think how much money there is to be made, or we could just eat the way your bodies were meant to eat. What kind of value is that going to get for 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 compare the microbiome, so vegans versus omnivores. I'm found that vegans 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 and what the bacteria were making was large, the effect of 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. I mean, this very modest difference juxtaposed against the significantly enhanced dietary consumption of fermentable plant foods. I mean, 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. The market showed that you need to get at least 50 grams a day of fiber for colon cancer prevention. 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.