Feb. 13, 2017 -- At her house in Portland, OR, art teacher Julia Himmelstein always has a batch of kombucha brewing to satisfy her bottle-a-day habit. Himmelstein, 33, says both her paternal grandparents had colon cancer, and that’s made her interested in diets that might help prevent the disease.
Kombucha, a fermented sweet tea that Himmelstein has been brewing for the past year and a half, is just one of many such foods and beverages growing in popularity around the country. Fermented foods made Whole Foods’ top five food trend predictions of 2016. Kimchi, a condiment of pickled vegetables popular in Korea, is now on three times as many restaurant menus as it was in 2010. An estimated one in four consumers drink kombucha, according to a 2015 food trend report from Mintel, a market research group.
In addition to kombucha and kimchi, some of the more popular fermented foods are yogurt, sauerkraut, kefir, a fermented milk beverage, and tempeh, made from fermented soybeans.
Users like Himmelstein hope -- and some early research suggests -- that the beneficial bacteria found in fermented foods may promote gut health by increasing its number of healthy bacteria.
“If you’re consuming a diet rich in fermented foods, you’re essentially bathing your GI tract in healthy, food-related organisms,” says food scientist Robert Hutkins, PhD, a professor at the University of Nebraska-Lincoln whose lab focuses on the link between fermented foods and human health.
An estimated 100 trillion microorganisms make a home in your gut, and they play a big, though not yet fully understood, role in your health. They influence metabolism and the immune system, and they may be involved in the development of colorectal cancer, obesity, and diabetes.
“If the good bugs in the gut outnumber the bad bugs, you’re less likely to develop some of the conditions that we know are highly associated with obesity and certain cancers and a whole host of things,” says Cleveland Clinic dietitian Kristin Kirkpatrick.
During fermentation, live bacteria break down food components such as sugar, making it easier for you to digest and absorb its nutrients.
Fermentation also can boost the nutritional value of certain foods. In some cases, it can produce a variety of B vitamins in foods that did not contain them before they were fermented.
“Fermented foods produce many active compounds that are beneficial to us,” says Zhaoping Li, MD, PhD, a professor of medicine and chief of the division of clinical nutrition at UCLA.
And, adds Los Angeles-based dietitian Lori Zanini: “Fermentation allows for nutrients to be better absorbed and used by the body.”
What are the Health Benefits of Fermented Foods?
In a recent review of studies on fermented foods, Hutkins and his colleagues list many potential reasons to add them to your diet. Yogurt, for example, may help you avoid heart disease and type 2 diabetes. Kimchi, meanwhile, may reduce your odds of diabetes and obesity.
Researchers have also studied fermented foods’ effect on gut problems. One study found that fermented milk eased symptoms of irritable bowel syndrome, possibly due to beneficial changes in gut bacteria that such foods bring.
Other fermented foods appear to relieve the diarrhea that people often suffer after taking antibiotics. Antibiotics disturb the balance of gut bacteria, and diarrhea can follow. The probiotics -- or healthy bacteria -- in fermented foods appear to help restore that balance and ease diarrhea.
“These studies point to associations between these foods and reduced disease and better health in people whose diets are rich in fermented foods,” says Hutkins.
But the studies don’t prove fermented foods caused these changes, and more research is needed to show a clear cause and effect between eating them and improved health, Hutkins says.
“If you do have some digestive issues, fermented foods may help to some degree, but there’s not very strong science behind it.”
“The research on their health benefits is lagging behind the current interest in fermented foods,” says Hutkins. He says that scientific studies of such foods -- and foods in general -- can be difficult to do.
Should You Add Fermented Foods to Your Diet?
While there’s some evidence that fermented foods may strengthen the immune system, Li is not convinced.
“If you’re healthy and you eat a good diet, you won’t see any benefits,” she says. “Your healthy diet will give your gut all the healthy bacteria it needs, so there’s really no point in spending the money.”
If you do want to try them, Kirkpatrick recommends starting slowly. “Start small and see how your gut reacts.”
How much should you eat? Nutritionists say everyone is different, so it comes down to trial and error. Kirkpatrick says people who eat a single serving a day tend to have healthier gut bacteria. Zanini, a spokeswoman for the American Academy of Nutrition and Dietetics, often recommends two to three servings of fermented foods per day.
“But you need to listen to your body,” she says. “If you are having stomach discomfort, that would be a sign to tone it down.”
Also, keep in mind that these foods will add calories to your diet -- some more than others. Kombucha, for example, has a lot of sugar, as do many varieties of flavored yogurts. If you make them a part of your daily diet, be sure that you change what you already eat, says Li.
“In general, most of us eat too much food already,” she says. “Anything you add to your diet -- even if it’s healthy -- may not be a good thing because by overeating, you increase the burden on your body and you increase inflammation.”
Be aware, too, that fermented foods can be an acquired taste. Many have a distinct sourness to them that people often find unfamiliar and, at first, off-putting. When Hutkins first started his research into fermented foods over 20 years ago, he was not a big fan of the flavor. That’s changed.
“The more I studied them, the more I began to experiment with them, and now they are a part of the family diet,” he says, listing kimchi, sauerkraut, miso, and soy sauce among his favorites. You can also make your own fermented food, like Himmelstein, who in addition to kombucha has made kimchi and buttermilk. Classic guides like Sandor Katz’s Wild Fermentation, as well as numerous online tutorials, can teach you how. Your local community college also may offer courses.
Most people, however, will rely on their local markets for fermented foods. Hutkins recommends that you head to the refrigerated section and seek out sauerkraut and other items there. Some brands will advertise that they contain live organisms. Those are the ones to choose. Jarred and canned sauerkrauts and other fermented foods all undergo heat processing, which kills most if not all of the beneficial bacteria.
Finally, don’t think that fermented foods are a cure-all, Li emphasizes, or that eating them will offset less healthy foods that you eat on a regular basis.
“Eat fermented food as part of an overall healthy dietary pattern,” says Li. “That’s the right way to go.”