10/08/2018
Long-term dietary intake influences the trillions of microorganisms residing in the human gut, but how rapidly and reproducibly does the human gut microbiome responds to short-term diet change?
The animal-based diet increases the abundance of bile-tolerant microorganisms and decreases the levels of Firmicutes that metabolize dietary plant polysaccharides. The change happens quickly. Within two days, one type of bacterium that flourishes under the dairy and meat-rich diet has been linked to inflammation and intestinal diseases in mice.
What about in human? To figure that out, the researchers got nine volunteers to go on two extreme diets for five days each.
The first diet was all about meat and cheese. Then, after a break, the nine volunteers began a second, fiber-rich diet at the other end of the spectrum.
The effects of all that meat and cheese were immediately apparent within 1-2 days. In particular, microbes that "love bile" started to dominate the volunteers' guts during the animal-based diet.
Bile helps the small intestines digest fats. So people make more bile when their diet is rich in meat and dairy. Why is this important? Because blooms of Bilophila cause inflammation and colitis in mice through flagging down the T-Helper cells, which lead to inflammation in the gut. There needs to be more human studies to find whether this concept applies to humans, but in the meanwhile, I recommend to my patients, and to genetically susceptible patients, to avoid meat and dairy, which could lead to colitis or inflammatory bowel disease.
Reference:
Nature, volume 505, pages
559–563 (23 January 2014)
