Low Fiber Intake Harms Gut Barrier and Microbiome Health

Full analysis

Dr. Chris Thompson, chief of interventional gastroenterology at Mass General Brigham and professor at Harvard Medical School, explains that when people don't consume enough fiber, gut bacteria run out of their preferred food source and begin consuming the mucus layer that lines the intestine. This damages the gut barrier and reduces production of butyrate — a short-chain fatty acid that gut bacteria make from fiber and that is essential for maintaining tight junctions (the seals between intestinal cells that keep bacteria from leaking into the bloodstream). Thompson recommends fiber intake targets of roughly 35 grams per day for men and 25 grams for women, noting that a World Health Organization review found the vast majority of people in Western countries fall well short. Constipation — defined as fewer than one bowel movement every three days, with hard stools — is an early sign of insufficient fiber. Recent studies using resistant starch (a type of fiber found in raw or minimally processed starches like powdered potatoes) at about 40 grams per day showed significant improvements in fatty liver disease and insulin sensitivity.