Kombucha is everywhere these days, from small city bodegas to hip cafés to mall food courts. Whole Foods stocks at least a dozen varieties of this fermented tea beverage. You know it has gone mainstream when PepsiCo buys a kombucha drink manufacturer, KeVita.
Kombucha is one of the fastest-growing products among “functional beverages” (meaning they supposedly provide health benefits beyond basic nutrition, though there is no legal definition for the term in the U.S.). Between mid-2017 and mid-2018, U.S. retail sales of kombucha increased by nearly 50 percent.
With its origin dating back to ancient China, traditional kombucha is brewed tea (typically black tea but also green or oolong) that is mixed with sugar and fermented with live microbes (touted as “probiotics”), which create carbon dioxide, organic acids like acetic acid, and other substances. Sometimes powdered tea or even coffee or other non-tea bases are used today. Called SCOBY (symbiotic culture of bacteria and yeast) or the “mushroom,” the live cultures can be reused indefinitely to make subsequent batches of kombucha. Home brewers often share their SCOBYs.
Some people drink kombucha because they like its flavor (which varies in sweetness and sourness) and touch of fizziness. Others consume it because of the numerous health claims made for it—that kombucha “detoxifies” the body and can, for instance,boost the immune system, improve digestion, increase energy, relieve arthritis, ease depression, relieve headaches, help eyesight, prevent menstrual cramps, lower cholesterol, and reduce the risk of cancer, hypertension, diabetes, and heart disease.
One website says that drinking kombucha may slow aging, citing a Chinese fruit-fly study (available only in Chinese). Another online proponent claims that kombucha can aid in weight loss, citing an unrelated vinegar study. Kombucha was once popular in the HIV/AIDS community, apparently because of the therapeutic claims made for it.
In 2011, the UC Berkeley Wellness Letter was rather negative about kombucha, noting the lack of evidence that it was a cure-all, as proponents assert, as well as a concern about possible contaminants. So where are we now?
Combing through the kombucha science
Lab studies on kombucha have reported antioxidant, antimicrobial, anti-cancer, and liver-protective properties—with increases in polyphenols (antioxidants) and free radical scavenging ability corresponding to increases in fermentation time. The polyphenols produced during fermentation—as well as those found naturally in the tea—are thought to be the compounds responsible for any potential health benefits.
But studies in people are lacking, and kombucha marketers and advocates are misleadingly extrapolating results from animal models and cell studies on kombucha—and on fermented foods overall—to make unsubstantiated and far-reaching claims about kombucha’s supposed benefits in humans. That is, researchers have yet to determine whether any of the biological effects seen in lab studies actually occur in humans who drink kombucha.
In fact, when University of Missouri researchers searched the English-language scientific literature for published kombucha studies through 2018, they found just one in people, with no other human research even reported to be in progress. That study, from India, found reductions in blood sugar in people with diabetes who drank kombucha daily for three months. But it was a small study—and it lacked a control group, so the results are meaningless.
Still, kombucha may contain significant levels of some B vitamins and trace amounts of other nutrients, along with polyphenols and other potentially beneficial compounds. And consuming fermented foods and beverages in general may have some health benefits.
Kombucha products: not all created equal
What exactly is in that bottle of kombucha you might pick up at the market depends on several variables, including aspects of the fermentation process (the pH, temperature, and fermentation time), the types of live cultures used or added, and whether the product was pasteurized or not (see below). Also, companies often add other ingredients after fermentation, including fruit juices, apple cider, sparkling water, flavorings, sugar (as evaporated cane juice or apple juice concentrate, for instance), and some vitamins (such as vitamin C). Bottled kombucha typically has about 25 to 50 calories and 4 to 10 grams of sugar per 8 ounces. There is no definition of what “authentic” kombucha is, though a nonprofit trade association, Kombucha Brewers International, is working on one.
Keep in mind that as with many fermented products, kombucha contains small amounts of alcohol. However, commercial kombucha can be sold as a non-alcoholic beverage if the alcohol content is less than 0.5 percent. Some homemade kombucha, on the other hand, may contain about 3 percent alcohol (for comparison, light beers are typically 4.2 percent alcohol). Like the tea it’s made from, kombucha also contains caffeine.
Is kombucha safe?
Drinking kombucha has been associated with adverse effects, but that was because it was often brewed at home under nonsterile conditions, as well as produced in ceramic pots that can leach lead. Home brewing or improper commercial production can also potentially result in contamination with mold, bacteria, or other disease-causing microorganisms.
Nowadays, kombucha is commercially produced using procedures that involve a food safety plan approved by the FDA and that follow “good manufacturing practices” (GMPs). These safety measures include using sanitary equipment and maintaining proper water temperature and pH (a measurement of acidity/alkalinity, which can affect microbial growth and hence contamination risk).
Kombucha can be pasteurized or unpasteurized (“raw”); some bottles contain preservatives like sodium benzoate and potassium sorbate to increase the shelf life. Pasteurization kills any harmful microbes and stops fermentation—thus limiting the alcohol content—but it also kills the live cultures, which kombucha purists say diminishes the beverage’s putative health benefits. That’s probably why pasteurized kombucha often has live cultures added afterward. Still, unpasteurized kombucha is safe to drink if it’s made following GMPs and other food-safety practices.
If you’re new to drinking kombucha with live cultures, it’s typically recommended that you start gradually (no more, say, than a half cup a day), since the microbes could cause gastrointestinal issues, including flatulence. People with impaired immunity should avoid kombucha with live cultures, whether brewed commercially (because of concerns that the organisms could negatively impact their immunity) or brewed at home (because of the additional contamination concern). Anyone who needs to avoid alcohol (including pregnant women and recovering alcoholics) should be aware that alcohol is present in kombucha, even if at very low levels in commercially bottled products—and at higher and varying amounts in home-brewed kombucha.
As a tea, kombucha may indeed have healthful properties, but well-controlled studies are still needed to determine who, if anyone, would benefit, as well as what quantity would have to be consumed to get any effects. If you’re healthy and you like the taste of kombucha, enjoy it. (Many people find it unpleasant, to put it kindly.) Check the labels on commercial products to see what may have been added and to find ones that are lower in added sugar.
But don’t expect kombucha to be a fountain of youth or a cure for any medical condition. And if you brew your own or are going to sample someone else’s homemade kombucha, it’s extremely important that proper safety methods be followed.
This article first appeared in the UC Berkeley Wellness Letter.
Also see Probiotics Pros and Cons.
Published February 04, 2020