ALICE CALLAHAN
Breweries sell craft kombucha on tap. Fruit vinegars and cultured chile pastes are featured on five-star restaurant menus. Walmart and Target stock kimchi and kefir.
Fermented foods have been popular in the United States for decades, but more recently, they have been thrust into the national spotlight.
In January, the Trump administration released new dietary guidelines that recommended, for the first time, that Americans eat sauerkraut, kimchi, kefir and miso for better gut health. And Health Secretary Robert F Kennedy Jr often promotes the benefits of sauerkraut and yogurt, saying they helped him lose weight and sharpen his thinking.
Humans have been fermenting foods for thousands of years. What does the science show now about how they may affect our health? We asked experts to explain.
They’re defined as any foods or drinks that have been transformed by microbes such as yeast, bacteria and fungi in ways that preserve and infuse them with tangy, savory, fruity or funky flavors, said Robert Hutkins, an emeritus professor of food science at the University of Nebraska-Lincoln.
Milk can turn into yogurt and kefir; vegetables become sauerkraut and kimchi; fruit is transformed into vinegar and wine; wheat is fermented into sourdough and beer. Even chocolate and some coffee is fermented, said Maria Marco, a professor of food science at the University of California, Davis.
Research on their health effects is limited, Marco said. But some studies suggest that the foods (excluding alcohol) may offer a few benefits. In a trial published in 2021, for instance, researchers split 36 healthy adults into two groups: one that ate a lot of fermented foods like yogurt, kimchi and kombucha and another that ate plenty of fiber-rich foods like legumes, whole grains, fruits and vegetables. After 10 weeks, those in the fermented food group had significantly lower levels of inflammatory markers in their blood and more diverse gut microbes than they did at the start of the study. Those in the fiber group had no changes in those measures.
Other research has found associations between fermented food consumption and less risk of eczema as well as kimchi consumption and lower rates of obesity; yogurt consumption and reduced risks of Type 2 diabetes and weight gain; and sauerkraut consumption and fewer irritable bowel syndrome symptoms.
Not all research has been positive. Some studies have found higher rates of stomach and esophageal cancers in people in East Asia who ate a lot of kimchi and other fermented vegetables, said Suzanne Devkota, director of the Cedars-Sinai Human Microbiome Research Institute. The evidence for the cancer link is weak, though, she said.
Many fermented foods are healthful in their own right, Marco said. A serving of kimchi or sauerkraut counts as a serving of vegetables, for instance, and yogurt and kefir provide calcium, potassium and protein. The microbes that ferment foods can also help with digestion and the absorption of nutrients, and even create nutrients of their own, said Dr Sean Spencer, a gastroenterologist and microbiome scientist at Stanford.
We have enough evidence to support incorporating more fermented foods into your diet, Spencer said such as having yogurt for breakfast, adding kimchi to eggs or sandwiches, or making salad dressings with apple cider vinegar. People who are immunocompromised, however, should be cautious with fermented foods that contain live microbes, such as those labeled raw, unpasteurized or as containing live cultures (typically found in refrigerated sections).
Such people may not be able to handle the “bacterial load” present in fermented foods, even if the bacteria are “friendly,” Devkota said. While beer, wine and other types of alcohol are technically fermented foods, it’s best to limit them, Marco said, given their established health risks.