In ancient Europe and Asia, sugar and tea were relatively scarce commodities. So kombucha—a fermented tea produced by feeding sugar to bacteria and yeast—was a high-end beverage, a sign of privilege, says Zhaoping Li, professor of medicine and chief of the division of clinical nutrition at the University of California, Los Angeles.
Sugar and Lipton come much cheaper today. But kombucha can still set you back $3 a bottle or more, even if you buy it at Wal-Mart (where, yes, it's now available). And though proponents proclaim the fizzy brew a cure-all, little research on humans—and only a few studies in animals and petri dishes—back any of these claims, Li says.
"There are people out there telling you—it'll cure cancer, it'll cure diabetes, it'll cure cardiac illness, it'll build your immune system, it'll prevent herpes, it'll reverse AIDS," says microbiologist Heather Hallen-Adams, an assistant professor in the food science and technology department at the University of Nebraska-Lincoln. "It might have some placebo effect, but anything that can cure everything basically doesn't cure anything."
The health benefits of kombucha are largely attributed to probiotics, the good-for-you microbes like Lactobacillus present in the SCOBY. That's short for symbiotic colony of bacteria and yeast—a blend of bugs that forms a floating film called a pellicle on top of kombucha as it brews. It appears vaguely fungal, which is why kombucha is sometimes called "mushroom tea" despite its lack of relation to shiitakes or cremini.
The yeast and Lactobacillus convert sugar into lactic acid and ethyl alcohol, Hallen-Adams explains. Then, acetic acid bacteria like Acetobacter and Gluconacetobacter convert the alcohol into vinegar. It's true that so-called lactic acid bacteria are the good guys—credited with improving the symptoms of irritable bowel syndrome and other gastrointestinal conditions, reducing the side effects of antibiotics, and treating yeast infections, among other perks. They're an essential part of what's called the microbiome, the balance of bacteria that lives within our bodies.
Li believes in the importance of bacterial diversity—she's studied the microbiome and calls beneficial bacteria "our good neighbours." "They're part of us—the microbes," she says. "We need to be very mindful and take care of them."
But, she points out, there are at least 500 different species of bacteria inhabiting our guts, for a total of 300 trillion microorganisms. Even concentrated probiotic capsules contain only about five species and 50 billion bugs, and kombucha serves up even smaller quantities. That's far from enough to make any real difference in health, Li says.
And as with any probiotic product, it's tough to know exactly what you're getting, Hallen-Adams says. The microbial cocktail each serves up depends not only on the contents of the tea and the SCOBY, but also factors like the incubation temperature and how long the stuff's been sitting on the shelf.
"At the time you bottle, or at the time you start [fermenting], you might know that you have 5 million colony-forming units of Lactobacillus reuteri," she says. (Even the way bacteria are typically measured in the lab makes it clear you're only estimating—a colony-forming unit is a cell or group of cells with the potential to continue growing, given the right conditions.) "But at the time someone gets it, are they still there? When you tested your culture two years ago, has somebody new joined it and somebody left?"
You have more control if you brew kombucha yourself, which Hallen-Adams does as a classroom exercise. But you also run the risk of contamination if conditions aren't completely sterile (Hallen-Adams says she's tasted her own, but said she feels far more comfortable with a store-bought bottle). "You're leaving out a sugar rich solution out there," Li says. "It's not only the good bacteria that grow." Harmful pathogens like E. coli can proliferate, too.
While most people who home-brew don't get sick, there have been documented instances of illness either due to contamination or to high acid levels from fermentation. Experts like Li and Angie Murad, a wellness dietitian at the Mayo Clinic Healthy Living Program, advise against it, especially for older people or those with compromised immune systems from diseases like cancer and HIV.
Because it's brewed from tea, kombucha does contain polyphenols—antioxidant compounds that decrease damage to our cells, which left unchecked could contribute to cancer, heart disease, and other conditions, Murad says. One particular type, catechin, also fights harmful bacteria, Hallen-Adams says.
But while there's some evidence fermentation slightly boosts the polyphenol count, you can get most of the same benefits without any of the potential downsides just from sipping a cup of regular green or black tea, Li says. And tea, unlike kombucha, is completely alcohol-free. Even though the SCOBY contains bugs that feed on booze, you might still be left with more than the .5 percent that legally makes a beverage non-alcoholic, Hallen-Adams says. In fact, the US Alcohol and Tobacco Tax and Trade Bureau has repeatedly warned kombucha producers about this hazard. Even that amount of booze problem for people sensitive to alcohol or those taking medications that interact with liquor, Li says.
Provided that doesn't describe you and you have a healthy immune system, swapping out a beer or a sugary soda for a sour, bubbly bottle of kombucha now and then probably won't hurt you and might save you a few calories (if you go for a brand without sugar added, there's about 60 calories per serving, half that in soda, Murad says).
But if it's a probiotic boost you're seeking, Hallen-Adams recommends yogurt or kefir instead—it boasts more good bugs, has been more solidly linked to health benefits (including a reduced risk of type 2 diabetes, abnormal cholesterol levels, and obesity) and fewer risks. As Murad points out, it delivers other nutrients like protein, calcium, and vitamin D.
Besides, you don't necessarily need to ingest more bacteria, even the beneficial types. "You have good seeds, you just need to take care of them. You don't need to keep planting in poor conditions," Li says. In other words, you're better off nurturing the flora already growing in your gut with high-quality soil and fertilizer, aka a healthy diet full of vegetables, fruits, and bacteria-feeding fiber. "If you really want to grow the garden with rich variety, take good care of it by eating right."
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