The best sources of dietary fiber are whole plant foods, such as fruit, vegetables, nuts, seeds and grains. Scientists are making progress understanding how a fiber-rich diet can help with chronic disease In the world of dietary trends, proteinmaxxing is taking a back seat to the new obsession: ramping up on fiber. Since the summer of 2025, Instagram has racked up more than 10,000 posts captioned with #Fibermaxxing and other fiber-forward hashtags — and the flood doesn’t appear to be dissipating.
The trend is a nod to our species’ history — and to how much our diet has changed. With the dawn of agriculture about 12,000 years ago, and the advent of modern food processing some 200 years ago,many people have abandoned historic levels of fiber consumption. That’s especially the case in developed countries (studies suggest that 95 percent of Americans don’t get enough), though it’s happening around the world.
And that change has disrupted our microbiome — those myriad microbes that dwell in our digestive system — with concerning consequences for our health. Walter is part of a community of microbiologists, nutritionists and other researchers who are exploring fiber’s biological effects on bacteria in the gut and amassing growing evidence that fiber, and the microbes it feeds, protects us against diseases such as inflammatory bowel disease, colorectal cancer and diabetes. This, these experts say, does more than underscore the importance of fiber.
It may also lead to novel solutions — perhaps one day even personalized fiber prescriptions. The microbiome, as depicted in this illustration, is a diverse community of trillions of bacteria and other microorganisms that live in our gut. Growing evidence suggests it affects our health in multiple ways.
Dietary fiber helps to keep the microbiome populated with health-promoting bacteria. Dietary fiber molecules are types of carbohydrates derived from plant foods — but unlike starch and sugars, they can’t be digested by the body. They pull their weight in other ways.
Until recently, nutrition scientists mainly classified fiber as insoluble (such as wheat bran) or soluble (such as pectin in fruit), based on its ability to dissolve in water. Categorization today is more sophisticated, considering properties such as bulking capacity (how well fiber holds on to water, increases feces size and regulates bowel movements); fermentability (how well it is broken down by microbes in the gut); and viscosity (how much it thickens into a gel in the digestive system). Examples of foods high in fiber of various types include beans and legumes, nuts and seeds, fruits, vegetables and grains**.** The study of the relationship between fiber and health dates back to at least the 19th century, when a handful of surgeons, physicians and medical researchers took an interest in diet as a determinant of disease.
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