“BLAH, BLAH, BLAH, bacteria are the best!” studies seem to shout everyday. But it’s partially true: These often-overlooked microbes (at least from a nutritional standpoint) are vital for a multitude of bodily functions (at least the beneficial ones)—and we’re now beginning to understand how powerful they really are.

To wit: Simply eating whole grains can affect the populations of bacteria living in our gastrointestinal tract, according to a new trial published in the American Journal of Clinical Nutrition. For the first two weeks of the eight-week study, the 81 participants ate a “Western diet” high in refined grains. Then, in the last six weeks, researchers broke participants into two groups, one of which stayed on the Western diet, while the other half switched to meals high in whole grains. Both diets were similar in calories, fruits, veggies, and protein, and were created to not affect weight.

To find out how the whole grain–heavy diet affected the subjects, stool samples were taken and the abundance of short chain fatty acids—which are produced by good bacteria—was calculated. (We don’t wanna know how, but the experimental methods are all spelled out here.) The whole-grain eaters had more of the acids produced by beneficial bugs, and a decrease in a type of bacteria known to cause inflammation.