Gut health is having a moment. From the rise of so-called “fibermaxxing” to growing rates of colorectal cancer among younger adults, more Americans are paying closer attention to what’s happening inside their digestive systems — and what they’re eating to support it.
At the center of that conversation right now is fermentation, one of the oldest methods of food preservation known to humanity. The federal government’s most recent dietary guidelines now specifically encourage Americans to eat more fermented foods, giving the trend an official stamp of approval.
Fermented foods have also gained a following among supporters of Health Secretary Robert F. Kennedy Jr.’s Make America Healthy Again movement. And while health experts have pushed back on some of that movement’s other dietary claims — including unproven ideas about raw milk and seed oils — the science does support some benefits of eating fermented foods.
Fermentation itself is a process where naturally occurring microbes, including bacteria and yeast, break down and preserve food. Humans have been doing it for thousands of years, long before refrigerators existed. Many cultures around the world have their own traditional fermented staples: yogurt, kimchi, sauerkraut, and South Indian dishes like idli and dosa are just a few examples.
Doctors and dietitians say fermented foods can be a great addition to nearly anyone’s diet — but they caution against reaching for new, mass-produced products that claim to offer the same benefits.
“We’ve been doing this for ages and we just found out more recently that it’s actually helped our gut health,” said Dr. Lisa Ganjhu, a gastroenterologist with New York University Langone Health.
But being fermented doesn’t automatically make something a health food. As Dr. Ganjhu pointed out, “Beer and wine are fermented foods, but they’re not necessarily probiotics. If anything, they influence our own microbiome in more of a negative way.”
Barbara Olendzki, director of the University of Massachusetts Chan Medical School’s Center for Applied Nutrition, said she advises people to focus on “whole fermented foods” — things like fermented beets or green beans — along with staples such as yogurt, kefir, kimchi, sauerkraut, and tempeh.
The microbes found in fermented foods essentially begin the digestion process for you, breaking down compounds and changing what’s available for your body to absorb. The bacteria also help keep your gut in balance by competing with less beneficial bacteria already living in your intestines.
Researchers are still working to fully understand exactly why fermented foods are so beneficial. “What is it that makes the fermented foods so healthy? The answer is we’re still working on it,” said Dalia Perelman, a research dietitian at Stanford University.
Some fermented foods, like yogurt, deliver live probiotics directly to your system. Others, like sourdough bread, provide little to none because the baking process kills off the microbes. Still, Perelman noted there is evidence that some fermented foods offer benefits even without live microbes present.
Experts are skeptical of sodas, chocolate, and other heavily processed products that market themselves as probiotic. Even probiotic supplements are essentially trying to recreate what naturally develops in traditionally fermented foods, Perelman said.
“Consumers are getting excited about it and trying to choose products that are fermented and with the idea that it’s very ‘gut healthy,’ which is not a clinical definition,” she said. “And then the marketing is running with this trend.”
Dr. Ganjhu also warned against sugary fermented products, explaining that extra sugar feeds harmful bacteria rather than the beneficial kind. She recommends looking for products that list “live cultures” on the label — not just the word “probiotic.”
“The best yogurt you can have is just plain, fermented milk with culture,” she said. “Let it do its business.”
For most people, fermented foods are considered safe. Beyond their health value, they also add unique and varied flavors to meals. However, Perelman noted that people with weakened immune systems or irritable bowel disease should speak with their doctor before making big changes to their diet, as reactions can vary depending on the type of fermented food consumed.
Olendzki added that some people may notice bloating, gas, or other discomfort when they first start eating more fermented foods, as their gut adjusts to the change.
“If you feel good, keep drinking it. You don’t feel good? Stop,” Dr. Ganjhu said, noting that the same foods can affect people very differently.
As for which fermented food reigns supreme, experts say there’s no definitive scientific ranking. The better approach is variety — eating many different types of fermented foods regularly rather than relying on just one.
Dr. Ganjhu suggested thinking about fermented foods in categories, such as milk-based options like yogurt and kefir, and fiber-based choices like kimchi and sauerkraut. Perelman recommended aiming for about two servings a day.
Fermented foods should also be part of a broader, balanced diet, so the beneficial bacteria you’re adding to your gut have plenty of fiber-rich prebiotics to feed on.
“Just go slow and drink a lot of water. It also matters what the rest of the diet looks like,” Olendzki said. “It’s not just one thing.”
