Researchers at the University of Michigan have discovered something unsettling about our gut bacteria: if not properly fed, it can begin to dine on our colons. Yes, our colons. A U of Michigan news release reports that researchers at the school transplanted 14 bacteria that normally grow in the human gut into mice born and raised with no gut microbes of their own. They also infected some of the mice with a bacterial strain that does to mice what certain strains of Escherichia coli can do to humans – cause gut infections that lead to irritation, inflammation, diarrhea and more. Here’s what they found: the natural protective mucus layer stayed thick, and the infection didn’t take full hold, in mice that received a diet that was about 15 percent fiber from minimally processed grains and plants. But when the researchers substituted a diet with no fiber in it, even for a few days, some of the microbes in their guts began to munch on the mucus. They also tried a diet that was rich in prebiotic fiber – purified forms of soluble fiber similar to what some processed foods and supplements currently contain. Nope. The diet resulted in a similar erosion of the mucus layer as observed in the lack of fiber. The researchers saw that the mix of bacteria changed depending on what the mice were being fed, even day by day. Some species of bacteria in the transplanted microbiome were more common – meaning they had reproduced more – in low-fiber conditions, others in high-fiber conditions. Most concerning: the four bacteria strains that flourished most in low-fiber and no-fiber conditions were the only ones that make enzymes that are capable of breaking down the long molecules called glycoproteins that make up the mucus layer. The bottom line: eat fiber before your gut bacteria eats you.