 Colon cancer risk in westernized populations may be reduced by decreasing the intakes of animal products, blaming aggressive factors such as animal protein and fat. We've explored how animal protein can putrify and produce the rotten egg gas, which may be toxic to DNA, but what about the fat? It can simulate the synthesis and secretion of bile acids into the intestine. That's what bile does—helps the body digest fat. So more fat in the intestines means more bile in the intestines, which wouldn't be a problem, except bile acids have long been suspected as being carcinogenic, especially secondary bile acids. See, bile acids stimulate the growth of bacteria which convert the primary bile acids our liver makes into secondary bile acids, and secondary bile acids have been shown to be cancer-causing. So this could help explain why fat-rich diets are correlated with colon cancer. My saturated fat intake is associated with elevated levels of bile, which is what you tend to see in people with colon cancer, and so are considered tumor-producing factors in colorectal cancer development, and perhaps breast cancer, as these secondary bile acids can get absorbed into the bloodstream and circulate throughout the body. This may help explain the extraordinarily low rates of colon cancer in sub-Saharan Africa, with native Africans putting out just a fraction of the secondary bile acids compared to African Americans. Well, if a diet high in animal fat stimulates the growth of these toxic and carcinogenic secondary bile salt-producing bacteria, what about people who don't eat animal fat? We've known for about 40 years that those eating plant-based diets have less bile in their stools, and reduce capacity to create colon carcinogens. Those eating vegetarian produce just a fraction of some of the secondary bile acids that's implicated in cancer, about 70% less. Put people on a plant-based diet, and within just a week, the bacterial enzyme activity produced these secondary bile acids is cut in half, and within a month their presence is cut in half as well. One of the most important toxic effects of these bile acids, the BAs in our BMs, is the increased production of free radicals. That's one of the ways they can damage our DNA and undermine our DNA repair pathways. Compared to this diet, if you switch people to a vegetarian diet for just 12 days, you can get a 13-fold drop in hydroxyl-free radical production. Hydroxyl radicals are one of the most destructive free radicals, which may increase colon cancer risk. They only last about a billionth of a second, and in that time can convert harmless substances in the bowel to DNA-damaging mutagenic substances, and bile acids are believed to promote this process. So fecal free radicals may activate carcinogens in the colon. On a standard American diet, the amount of free radicals produced in the stool is quite remarkable, corresponding to that which would be produced by a fatal dose of gamma radiation. So what do we do about it? What's an achievable practical measure to decrease free radical formation in our colon? Well, we could just eat a more plant-based diet, but there's not a lot of money in cauliflower and carrots, so instead we could attempt to colonize people colon with genetically engineered antioxidant-producing bacteria.