The wellness industry loves hero ingredients. 2025 was the year when protein dominated grocery aislesit appears in everything from popcorn to soda and even water. Currently, fibermaxxing The humble nutrient not only promises smoother, more satisfying poops, but it benefits metabolic health, heart health, and some. But where probiotics—another gut health darling that had its heyday as the go-to supplement a few years ago—will it be mentioned?
If you’re trying to optimize your gut health and digestion, is fiber or probiotics doing most of the heavy lifting? Below, experts help us unpack these two gut health all-stars and share which one comes out on top. But first, a quick update on both.
The benefits of fiber
The fiber found in plant foods is a type of carbohydrate that the body cannot digest – but the gut bacteria can. “When various dietary fibers reach the large intestine, bacteria ferment them and produce short-chain fatty acids (SCFAs),” he says. Will Bulsiewicz, MDboard certified gastroenterologist and the author Plant Powered Plus. Butyrate is one important SCFA that not only strengthens the intestinal wall, but also protects your body against pathogens. Outside of the colon, SFCAs “regulate blood sugar, help cholesterol, and trigger the release of appetite-suppressing hormones like GLP-1 and PYY,” says Dr. Bulsiewicz. “They even optimize the immune system and reduce inflammation.” In addition to SCFA production, fibers promote the growth of beneficial bacteria and the passage and absorption of nutrients in the intestine. Federica Amati, PhD, MPH, RNutrchief nutritionist at ZOE.
And of course, much of fiber’s reputation comes from its digestive benefits, whether the problem is going to the toilet too much or too little… or just a generally unpleasant experience once you’re there. “Fiber improves bowel irregularity and makes stools bulkier and softer, helping things move more smoothly through the digestive system.” Felice Schnoll-Sussman, MD, MScsays a board-certified gastroenterologist at Weill Cornell Medicine and New York-Presbyterian YOURSELF.
Depending on your digestive problems, it may also help to clarify what kind of fiber you are getting. That’s right: there are two types…soluble and insoluble fiber– and each serves a different purpose. The former is water-soluble and can slow digestion, which Dr. Schnoll-Sussman says is useful for treating diarrhea and blood sugar. (“It can also lower cholesterol by binding to bile acids, which can be associated with a reduced risk of cardiovascular disease and obesity,” he adds.) Insoluble fiber, on the other hand, does not dissolve in water and can aid in intestinal transit, thus treating constipation.
