If You Do Not Feed Gut Bacteria Fiber, They Eat Your Protective Mucus
Microbes turn fiber into butyrate, the fuel that feeds colon cells and keeps the gut sealed.
Huberman Lab · Best Tools for Gut Health & Weight Loss | Dr. Chris ThompsonDr. Chris Thompson, an interventional gastroenterologist at Harvard and Mass General Brigham, says of gut microbes: "They need to be fed, and what they eat is fiber." Without fiber, microbes eat the mucus layer that protects the gut, part of a barrier that is remarkably thin.
When fiber does arrive, making use of it takes teamwork. One group of bacteria breaks fiber down into simpler compounds called acetate and lactate. Those compounds then feed a second group of bacteria, which convert them into butyrate, a short fatty acid.
Butyrate is the fuel that keeps the seal intact. The cells that line the colon live on it. It helps maintain tight junctions, the seals between neighboring gut cells that control what passes through. It also helps keep the colon acidic, which discourages harmful organisms, signals fullness through gut hormone pathways, and teaches the immune system what to attack and what to leave alone.
Miss the fiber and the chain breaks in order. The microbes chew through protective mucus, they make less butyrate, and without butyrate the tight junctions weaken. Scientists can measure the result as increased permeability, meaning those seals let more pass through than they should, and Thompson says it is tied by solid evidence to real illness, even if it does not explain everything.
You cannot get the same effect by swallowing butyrate, Thompson says, because it acts in the colon.
Questions people ask
How much fiber do I actually need?
Most U.S. guidelines suggest about 25 grams per day for women and 38 grams for men, and most people get far less. Beans, lentils, oats, berries, vegetables, nuts, and whole grains are among the richest sources.
Do fermented foods do the same thing as fiber?
They help in a different way. Fermented foods like yogurt, kefir, kimchi, and sauerkraut add live microbes and partly digested food, while fiber feeds the microbes you already have. Thompson says to take fermented foods in addition to fiber.
Can I just take butyrate as a supplement?
Thompson says swallowed butyrate would not reach the colon, where it needs to be to have its effect. In the gut, bacteria make butyrate from acetate and lactate produced from fiber.