Why Kombucha's Health Benefits May Be Exaggerated


Growing up in New York City, Sandor Katz couldn't get enough deli pickles. As a child in Virginia, Jessica Childs skipped the pickles and drank the briny juice directly from the jar. Devon Sproule was surrounded by fermented foods growing up on a hippie commune, but she didn't start drinking kombucha, a fermented tea, in earnest till she was an adult, to stave off illness during prolonged periods without health insurance.

Call them "fermies"—fermentation foodies. They are everywhere, from small towns to foodie-central Brooklyn. And the mounting interest in live-culture fermentation owes some of its success to their blend of locavorism, raw and probiotic diets, artisanal and do-it-yourself foodmaking, and, yes, a lack of health insurance. Mostly, though, it's the foods' reputation as detoxifiers and immune-system boosters that is pushing fermentation into the mainstream. But do the benefits of live-culture fermented drinks or foods extend beyond the anecdotal into scientific fact?

Though live-culture fermented foods include sauerkraut, kimchi, and kefir (a fermented yogurt drink with grains), the current clamor is for kombucha, a fermented tea with ancient roots in Russia, China, and Japan. Corporations have taken note: Celestial Seasonings and Honest Tea (in which Coca-Cola is a minority investor) sell their own versions of the drink. While extremely small, the beverage-market share of kombucha skyrocketed from $80 million nationwide in 2008 to $324 million in 2009, according to Kombucha Brooklyn, a small-batch brewer and distributor. But much of kombucha's appeal may come from its do-it-yourself applications.

"We always sell out our fermentation classes, whether it's kimchi or kombucha," agrees Taylor Erkkinen, owner of The Brooklyn Kitchen and The Meat Hook, which hosts four to five fermentation classes per month. Her store has sold out of home-brewing supplies.

"There's a revival, a resurgence of interest in fermentation, a huge amount of do-it-yourself activity in this realm," says Katz, who lives in Tennessee and teaches fermentation workshops throughout the country. He's the author of the fermenting bible Wild Fermentation. "I don't think it's happening in a vacuum. There's a major resurgence in people wanting to feel connected to their food, as well as some nutritional movements that emphasize the importance of live bacterial cultures."

Most fermented foods are not revolutionary: bread rises because yeast ferments it, grapes ferment with the assistance of yeast into an alcohol known as wine, and coffee beans are placed in a warm-water bath to ferment until a slimy outer membrane disintegrates, thanks to lactic bacteria. To make each of these, yeast, bacteria, or both release enzymes that break down a food's sugar and convert it to lactic acid or alcohol. Fermentation foodies, in contrast, create and consume live-culture ferments—foods that maintain living bacteria or yeast (and sometimes both) at the time of consumption. Bread is baked, coffee beans are roasted, and many other commercially available ferments, such as types of yogurt or pickles, do not qualify because they are heat-treated after the fermentation process, killing off living microbes.

In the case of kombucha, the fermenter adds a slimy silicone-like pancake called a SCOBY (symbiotic culture of bacteria and yeast) to a jar of sweet tea, starting a 10-day process. In the end, the bacteria will have consumed 95 percent of the sugar, leaving behind lactic acid, alcohol, and several B vitamins, according to a study of AIDS patients who used kombucha therapeutically during the 1990s.

Recently, the FDA cracked down on unpasteurized commercial kombucha, which has an unpredictable alcohol level. The high-end Whole Foods grocery chain removed unpasteurized bottled and on-tap kombucha from its stores as part of a recall from suppliers after allegations that the alcohol content went as high as 3 percent, far above the 0.5 percent limit for nonalcoholic beverages.

Devotees of kombucha say the live cultures have helped clear up their acne, soothe their heartburn, and quiet headaches. "There are some microbes that have found a competitive advantage by living in animals—typically they are toxins like salmonella and E. coli—and these are bacteria that use our bodies to replicate themselves, making us sick," explains Jessica Childs, a professional tempeh maker and former microbiologist who owns both Tempeh Shop Brooklyn and Kombucha Brooklyn with her husband, Eric. "So because microbes are in constant competition for limited space, the best defense we have against the microbes that make us sick is ingesting the ones that can survive and colonize our bodies while protecting us against the microbes that hurt us."

Devon Sproule is a touring musician in Virginia who is married to another touring musician. She credits ferments with helping her maintain her current lifestyle as she gets older, and with helping her husband with his acid reflux. "Being a nighttime person and a drinking person who doesn't have health insurance," says Sproule, "kombucha and other fermented foods are a lot about prevention."

But scientists and nutrition experts aren't convinced.

"Oh, please. Fermentation is a way to preserve foods and, therefore, the nutrient value of those foods," says Marion Nestle, Paulette Goddard professor in the Department of Nutrition, Food Studies, and Public Health at New York University. "But I'm not aware of convincing scientific evidence that they have special health benefits beyond [the preserved item's] basic nutritional value."

The evidence for kombucha's health effects is indeed slim: a 2003 study published in Biomedical and Environmental Science found that it improved and stimulated the immune systems of rats that had symptoms that mimicked Parkinson's disease and other disorders. However, that same year, a German review of all scientific research on kombucha found that it could not be recommended for therapeutic use because the risks outweighed the benefits. Memorial Sloan-Kettering's Cancer Center warns immunosuppressed people—such as patients undergoing chemotherapy—against using kombucha because of the possibility of contamination with a fungus called Aspergillus. A few cases of contamination with anthrax have also led to recommendations to avoid kombucha.

Meanwhile, those same live cultures are also found in non-heat-treated kinds of yogurt. Studies into the health benefits of Lactobacillus acidophilus in yogurt are more plentiful, possibly because yogurt has been on the market longer. An American Journal of Clinical Nutrition study found that women who ate yogurt reduced their chances of yeast infection by two thirds. And a 2000 Tufts University study found that consuming the bacteria helped maintain intestinal-tract health, especially for people with weakened immune systems, through an "immunostimulatory effect" in which the body reacts to the bacteria ingested, bolstering the immune system.

Despite the success of yogurt live-culture studies, one major impediment to studying the health properties of fermented foods is that they can vary widely because no two ferments form exactly the same way. So while kombucha may have some beneficial effects, it's really too new to the market for anyone to know. Nonetheless, as long as fermies continue to sing the praises of the fermented brew, it's likely to gain in popularity.

CORRECTION: The original version of this article suggested that Honest Tea was a subsidiary of Coca-Cola. In fact, Coca-Cola holds only a 40 percent share of the company. We regret the error.