A study, recently published in Nature, indicates that these changes can happen incredibly fast in the human gut—within three or four days of a big shift in what you eat. “We found that the bacteria that lives in peoples’ guts is surprisingly responsive to change in diet,” Lawrence David, assistant professor at the Duke Institute for Genome Sciences and Policy and one of the study’s authors, says. “Within days we saw not just a variation in the abundance of different kinds of bacteria, but in the kinds of genes they were expressing.” (Scientific American is part of Nature Publishing Group.) They also observed changes in the amount of bile acid secreted into the stomach, and found that bacteria native to our food—microorganisms used to produce cheeses and cure meats—are surprisingly resilient, and colonize the gut along with species already in our microbiome.
“The incredible quickness of this shifting is interesting,” David says, “for at least two reasons:” The first is evolutionary. These rapid changes, he says, could have been very useful for ancient humans. For hunters and gatherers, diet could be altered quickly and with little transition—weeks of nuts and seeds might be broken up by a sudden influx of meat from a successful hunt—and the ability to rapidly change the microbiome would ensure maximum nutrient absorption from even the most unfamiliar foods.
For modern humans, the rapid shift could be less adaptive. The 10 participants in the study switched to either a plant- or animal-based diet, with the former avoiding animal products and the latter eating milk, cheese and meat. In the subjects eating animal products the researchers saw a significant uptick in Bilophila wadsworthia, a bacteria known to contribute to colitis, a variety of inflammatory bowel disease, in mice. But the link hasn’t been studied in humans,
People should pay more attention to what they eat. But it rests on scientists to recognize that dietary discipline has these varied effects, and to understand what each component does so we can design healthier diets. This is just one study in the multiple studies in mic and humans dramatic changes in our diet, he says, could very well be the cause of “Western disorders” particularly inflammary bowel disease, obesity depression diabetes and autoimmune disease