Right now, on your favorite social media channel, someone is preparing a “poopy” breakfast loaded with bran and chicory root–enriched yogurt while someone with the handle “fiber daddy” is snacking on liquefied raw vegetables.

This is the world of “fibermaxxing” (“poopmaxxing” to some), in which people try to eat as much fiber as possible. Fiber-rich diets have been linked to lower risks of heart disease, digestive problems, some cancers, and other illnesses—and the idea seems to be that if a little fiber helps, a lot of fiber will help even more. Some people aim for up to 60 grams or more of fiber a day, much higher than the USDA’s recommendation of between 25 and 38 grams a day, depending on age and sex. Because most Americans are eating far less than that—closer to 10 or 15 grams—experts say that the trend isn’t exactly unwelcome but that your long-term diet might limit how much it benefits your health.

Fiber plays an important role in your digestive system. These plant-derived compounds can’t be digested by the body’s own enzymes; instead they pass largely untouched to the colon, where bacteria break some of them down through fermentation. The breakdown produces short-chain fatty acids (SCFAs) that are essential for health. One SCFA called propionate is linked to lower cholesterol and to helping the body feel satiated; another, called butyrate, is a key energy source for the cells lining the colon.

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Eating fiber also feeds the bacteria in your gut. Without fiber to supply their nutrients, gut microbes “basically start eating you,” gnawing away at the colon’s protective mucus lining, says Erica Sonnenburg, a microbiologist at Stanford University, who studies how diet shapes the gut. Once the mucus barrier is breached and colon cells start to suffer damage, the body launches an immune response, leading to “the simmering inflammation” characteristic of diseases common in Western countries, such as inflammatory bowel disease, obesity and type 2 diabetes. And because low-fiber diets mean fewer of the bacteria that produce SCFAs, the barrier has less help repairing itself, creating a cycle in which a weakened gut barrier and chronic inflammation get worse over time.

“Everyone in the industrial world has a depleted microbiome,” Sonnenburg says, in part because of chronically low-fiber diets. But fibermaxxing alone may not fix this problem once it has started. In a 2021 study Sonnenburg co-authored, people who doubled their fiber intake for four months showed no increase in their microbial diversity. And unfermented food appeared in their stool—a sign their microbiome wasn’t equipped to break down what they were eating. None of the 19 inflammatory proteins the researchers tracked decreased in the high-fiber group, either.

But people with the highest microbiome diversity from the start “definitely reaped the benefits,” Sonnenburg says, with an “immune system that was less inflamed.” For everyone else, there are ways to increase the diversity of bacteria in your gut. Participants who ate a high-fermented-food diet had more diverse microbes and saw reductions in some inflammatory markers.

People’s responses to fiber might also vary depending on which types of bacteria dominate their guts. Two of the main groups are Prevotella, which is more common in people who eat lots of plants and fiber, and Bacteroides, which appears more often in people eating Western, animal-heavy diets. One study tested how each type handled three different dietary fibers: fructooligosaccharides—a fiber in foods such as chicory and onions—and two arabinoxylans, which are fibers extracted from sorghum and corn bran. The Prevotella microbiome produced consistently high levels of the beneficial SCFAs; Bacteroides responded rather variably.

A small 2025 study found that a week of consuming arabinoxylan fiber reduced hunger for people with Prevotella-dominant microbiomes but had no effect on Bacteroides-dominant individuals, even though both microbiome types showed some increase in propionate production. And a 2024 study found a significant correlation between Prevotella abundance in the gut and levels of propionate—the SCFA linked to metabolic regulation and satiety.

But we should be cautious about reading too much into the Prevotella/Bacteroides divide, says Eric Martens, a microbiologist at the University of Michigan. He notes that their links to health benefits are correlations, with the underlying cause-and-effect relations yet to be established. What’s important is getting fiber from a variety of sources. Fiber is not all the same: it’s a diverse class of nutrients that vary in their chemical structure and solubility, with each type requiring different enzymes for breakdown. “If you’re eating a complex mixture of fibers, some at least are going to match well with the community that you have,” Sonnenburg says.

This is where fibermaxxers might go wrong: by relying too heavily on inulin and chicory root fibers. These are the cheap and highly soluble fibers found in prebiotic sodas, bars and yogurts marketed as high fiber. Because they’re so rapidly fermentable, they tend to cause gastrointestinal distress at around 20 grams a day, Martens says. Too much fiber overall can have a similar effect, often tied to serious gut discomfort and gas. Even psyllium husk works well for some people but can cause painful bloating and gas for others. “Pay attention to your own symptoms,” Sonnenburg advises. “Because everyone’s microbiome is unique, it’s hard to make a blanket recommendation for everybody.”

Any benefits of fiber are probably the result of a lifelong diet, not a passing fad. Martens recommends increasing gradually to about 35 grams a day, mostly by eating whole foods, rather than supplements and fortified foods, and sticking with them. The gut, he says, will adapt.