This recent study found that animal-based diets likely contribute to the development of inflammatory bowel disease. They do so by encouraging the growth of pro-inflammatory organisms in the intestine. The study also found that the intestinal microbiome (the collection of bacteria and other organisms that reside in the gut) can change – quite rapidly, within days – based on foods eaten:
Diet rapidly and reproducibly alters the human gut microbiome, Nature, December 2013
Here’s the full pdf from OpenWetWare (thanks to the authors!): Diet rapidly and reproducibly alters the human gut microbiome
Researchers had 11 volunteers (6 male), ages 21 to 33, consume both a plant-based diet (grains, legumes, fruits, vegetables. dietary fat: 22.1% of calories, dietary protein: 10.0%, fiber: 25.6 grams per 1000 calories) and an animal-based diet (meats, eggs, cheeses. dietary fat: 69.5%, dietary protein: 30.1%, fiber: “nearly zero”) for 5 days.
Here’s Table 5 from the study:
“The animal-based diet increased the abundance of bile-tolerant microorganisms (Alistipes, Bilophila and Bacteroides) and decreased the levels of Firmicutes that metabolize dietary plant polysaccharides (Roseburia, Eubacterium rectale and Ruminococcus bromii).”
It increased bile-tolerant organisms because more bile is excreted when more fat is eaten. Bile-tolerant organisms cause discomfort because they produce more hydrosulfuric acid.
“Increases in the abundance and activity of Bilophila wadsworthia on the animal-based diet support a link between dietary fat, bile acids and the outgrowth of microorganisms capable of triggering inflammatory bowel disease.”
A bit more data from the study:
- GI motility was significantly lower on the animal-based diet (median transit time of 1.5 days) than on the plant-based diet (1.0 days).
- DCA, a secondary bile acid known to promote DNA damage and hepatic carcinomas [liver cancer] accumulates significantly on the animal-based diet.
- Total fecal bile acid concentrations increase significantly on the animal-based diet.
- Bile acids have been shown to cause inflammatory bowel disease in mice by stimulating the growth of the bacterium Bilophila which is known to reduce sulfite to hydrogen sulphide. [Dissolved in water, hydrogen sulfide is known as hydrosulfuric acid.]
Growth of B. wadsworthia is stimulated in mice by select bile acids secreted while consuming saturated fats from milk. Our study provides several lines of evidence confirming that B. wadsworthia growth in humans can also be promoted by a high-fat diet. First, we observed B. wadsworthia to be a major component of the bacterial cluster that increased most while on the animal-based diet. This Bilophila-containing cluster also showed significant positive correlations with both long-term dairy and baseline saturated fat intake, supporting the proposed link to milk-associated saturated fats. Second, the animal-based diet led to significantly increased faecal bile acid concentrations. Third, we observed significant increases in the abundance of microbial DNA and RNA encoding sulphite reductases on the animal-based diet. Together, these findings are consistent with the hypothesis that diet-induced changes to the gut microbiota may contribute to the development of inflammatory bowel disease.
I often mention to people who experience GI discomfort that more fat in their meal will cause more bile acids to be released (bile emulsifies fat and aids in its digestion). And bile, or bile metabolites, irritate the lining of the colon (and have been implicated in colon cancer). Maybe I lose them at the word bile.
A meal of beans and other fermentable carbohydrates (broccoli, cabbage, onions, garlic, etc.), when consumed with a lot of fat, especially saturated fat of which dairy foods are a good source, can cause more distress than the same meal eaten with less fat.