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.

If you go online and search for Crohn’s disease and diet, or ulcerative colitis and diet, the top results are a hodgepodge of conflicting advice. What does the science say? If you do a systematic review of the medical literature on dietary intake and the risk of developing inflammatory bowel disease, Crohn’s disease is associated with the intake of fat and meat, whereas dietary fiber and fruits appear protective. The same foods are associated with the other major inflammatory bowel disease, ulcerative colitis: fat and meat, with a protective association found for vegetable intake.

Why, according to this meta-analysis of nine separate studies, do meat consumers have about a 50 percent greater risk for inflammatory bowel disease? One possibility is that meat may be a vehicle for bacteria that play a role in the development of such diseases. Meat contains huge amounts of Yersinia, for example. Yes, maybe antibiotic residues in the meat could be theoretically mucking with our microbiome, but Yersinia are so-called psychotropic bacteria, meaning they’re able to grow at fridge temperatures. It has been found to be significantly associated with inflammatory bowel disease, supporting this concept that Yersinia infection may be a trigger of chronic inflammatory bowel disease.

One reason why specifically animal protein was associated with triple the risk of inflammatory bowel disease, but plant protein was not, is because it can lead to the formation of toxic bacterial end products, such as the rotten egg gas, hydrogen sulfide. Hydrogen sulfide is not just one of the main “malodorous compounds in human flatus;” it’s a poison that has been implicated in ulcerative colitis. So, go on some meat-heavy, low-carb diet, and we’re not just talking about some “malodorous rectal flatus,” but increased risk of irritable bowel, inflammatory bowel syndrome, and eventually, colorectal cancer.

Hydrogen sulfide in the colon comes from sulphur-containing amino acids like methionine that are concentrated in animal proteins, though there are also sulfites added as preservatives to some nonorganic wine and nonorganic dried fruit. It’s the sulphur-containing amino acids that may be the more important of the two. Give people increasing quantities of meat, and you can get an exponential rise in fecal sulfides.

Specific bacteria, like Biophilia wadsworthia, can take this sulfur that ends up in our colon and produce hydrogen sulfide. And give people an animal product-based diet packed with meat, eggs, and dairy, and you can specifically increase the growth of this bacteria. People underestimate the dramatic effect diet can have on our gut bacteria. Give people a fecal transplant, and it can take three days to shift your microbiome. Take a powerful antibiotic like Cipro, and it can take a week. But start packin’ in the meat and eggs, and within a single day you can change your microbiome—and not for the better. You can more than double the bad bacterial machinery that churns out hydrogen sulfide, consistent with the thinking that diet-induced changes to the gut flora may contribute to the development of inflammatory bowel disease. In other words, the increase in sulfur compounds in the colon when you eat meat is “not only of interest in the field of flatology,” the study of human farts.

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