 The human gut has a diverse collection of microorganisms, making up some 1,000 species, with each individual presenting with their own unique collection. But it wasn't known whether this variation is on a continuum or if people cluster into specific, classifiable types, until this famous study analyzed the gut flora of people across multiple countries and continents and identified three so-called enterotypes. There were people who had lots of bacteroides in their gut, people who had a predominance of prevotella species, and people who stooled instead grew out of a lot of ruminate caucus species. Pretty amazing that with so many hundreds of types of bacteria that people would settle into just one of three categories. But they figure our guts are like ecosystems, just like there's lots of different species of animals on the planet. They aren't randomly distributed. I mean, you don't find dolphins in the desert. In the desert, you find desert species. In the jungle, you find jungle species, because each ecosystem has different selective pressures, like rainfall or temperature. Well, this early research suggests that there are three types of colon ecosystems. You can split humanity up into three types. People whose guts grow out lots of bacteroides type bacteria, those whose guts are better homes for a prevotella group bacteria, and those that foster the growth of ruminate caucus. And if you think it's amazing, they were able to boil it down to fit everyone into just one of three groups. Subsequent research on a much larger sample of people was able to fold ruminate caucus into bacteroides. So now everyone fits into just one of two groups. So now we know when it comes to gut flora, there are just two types of people in the world. Those that grow out mostly bacteroides, and those that overwhelmingly are home to a prevotella species. The question is why? It didn't seem to matter where you lived, male or female, how old or skinny you are. What matters is what you eat. This is what's called a heat map. Each column is a different grouping of bacteria, and each row is a food component. Red is like hot, meaning a close correlation between the presence of this particular bacteria and lots of that particular nutrient in the diet. Blue is like cold, meaning you're way off. A reverse correlation, meaning lots of that nutrient is correlated with very low levels of that bacteria in our gut. They looked at over 100 different food components, and a theme started to arise. This column is bacteroides, and this column is prevotella. Note how they're kind of opposites. When it comes to things like animal fat, cholesterol, animal protein, bacteroides is red, and prevotella is blue. When it comes to plant components like carbohydrates, prevotella is red, and bacteroides is blue. Here's a simplified version, clearly showing the components found more in animal foods like protein and fat are associated with bacteroides, with the Bacteroides entero type, and those found almost exclusively in plant foods are associated with prevotella. So no surprise African-Americans fell into the Bacteroides entero type, where most of the native Africans were prevotella. The reason this may matter is that Bacteroides species are generally associated with increased risk of colon cancer, our second leading cause of cancer death, yet almost unheard of among native Africans. The differences in our gut flora may help explain why Americans appear to have more than 50 times the rate of colon cancer.