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What Is Kombucha? Everything You Need to Know About This Fermented Tea

Isabel Smith, R.D., CDN
Certified Dietitian and Nutritionist
By Isabel Smith, R.D., CDN
Certified Dietitian and Nutritionist
Isabel Smith is a New York City-based dietitian, fitness expert, and founder of Isabel Smith Nutrition and Lifestyle.

You might recognize kombucha as the bubbly, fizzy drink that has taken the health food industry by storm. But what exactly is kombucha, and why is it so popular? It makes big promises, but does it live up to the gut-healing hype?

Here, we explain how kombucha is made, some of its health benefits, and why you might want to consider drinking it. It's time to know exactly why we love our booch.

What is kombucha?

Kombucha is a beverage made by combining green and/or black tea with sugar and certain strains of bacteria or yeast, then fermenting it for one week or more. During the fermentation process, at the top of the liquid a lumpy mixture called SCOBY1 forms. (Pro tip: SCOBY can be reused as a starter to brew another batch of kombucha!) The kombucha is then flavored with fruit, juice, and other herbs or spices, and can take on a wide variety of flavor profiles—ginger, berry, grapefruit, you name it.

During the fermentation process, lactic acid bacteria forms2 that may provide some probiotic benefits. (Various producers will add extra probiotics after the creation process as well.) 

Alcohol forms during the fermentation process, too, although typical amounts of alcohol in kombucha are around 0.5%, with 3% as the highest amount if it's home-brewed. In comparison, an average serving of craft beer can contain anywhere from 4% to 6% alcohol. Despite its small alcohol content, there is no law stating that you must be 21 or older to purchase kombucha, but people who are avoiding alcohol entirely should take precautions before consuming this brew. Kombucha is easily found in most retail grocery stores, health food stores, and drugstores.

Health benefits of kombucha.

Kombucha has been touted as having many health benefits, including: 

Gut health

Kombucha can be a source of gut-healthy bacteria. Kombucha naturally contains a species of lactobacillus bacteria (in the SCOBY) that can help to populate the gut with immune and digestive-healthy properties2. After brewing, sometimes bifidobacteria strains are also added—these bacteria help populate a healthy colon and promote healthy digestion (they help produce short-chain fatty acids, for instance). Any added probiotics would be labeled on the nutrition facts panel of the product.


Because kombucha is made from green and black tea, it has antioxidants and anti-inflammatory properties that those teas naturally contain. Green tea is a rich source of polyphenols, and research has shown it has powerful antioxidant effects3. Black tea is also a source of polyphenols and may provide anti-inflammatory properties4, as well as promote healthy blood sugar levels.

Mental health

Kombucha may also contain some brain-healthy, mood-boosting properties, thanks to its antioxidants and probiotic strains (both natural probiotics and those added, too!). A systematic review of 10 published studies found that probiotics could help alleviate depressive symptoms5. Kombucha also, as mentioned, populates the gut with healthy bacteria—since an imbalanced or damaged gut may drive a chronic stress response, a healthy gut could very well mean a healthy brain.

Weight loss 

Kombucha may also help to promote healthy weight due to the green/black teas. Green tea, in particular, contains both caffeine and a plant-based nutrient called catechin that has been found to help speed up metabolism6. Black tea may not contain the same catechins, but the antioxidants and polyphenols may be just as effective for weight loss7.

Blood sugar

Kombucha may also be beneficial in promoting healthful blood sugar. Though the research still needs more backing, one 2012 study (done on rats) indicates that kombucha may help to optimize liver function8, which may help with blood sugar control. We definitely need more research in this area, but it's promising!

Immune health 

Kombucha may also contain immune-healthy benefits, thanks to both the fermentation and lactobacillus bacteria found in the drink. A systematic review found that populating the gut with healthy bacteria (as kombucha does with probiotics) seems to promote general immune health9. The antioxidants from the tea itself (both black and green) can help support the immune system4 as well.

Health risks & possible side effects of kombucha.

While there are many health benefits of kombucha, there are possible health risks some individuals should take note of. For example, for people who are not used to drinking fermented beverages or eating fermented foods, a sudden onset of drinking kombucha could potentially lead to headaches, nausea, or other gut issues. These symptoms are more likely to occur if large quantities are consumed. Therefore, kombucha intake should be limited, and the beverage should be introduced into the diet gradually (in other words, you might not want to drink a gallon of kombucha if you're not used to eating fermented foods). The Centers for Disease Control (CDC) recommends drinking no more than about 4 oz. daily of kombucha10, which is drastically less than the typical serving size of bottled kombucha (usually between 12 and 16 oz.). 

In addition, because of the acidity of kombucha tea, it should not be prepared or stored in containers made from materials such as ceramic or lead crystal, which contain toxic elements that may leach into the tea. Glass is perhaps the safest material to both brew and store kombucha for longer-term use. 

Kombucha can also be high in sugar, depending on how it's made and how long it ferments. This means it's not necessarily a good choice for people who suffer from diabetes or other blood-sugar disorders. If you do suffer from those conditions, it's always a good idea to check the nutrition facts label of any bottled kombucha and choose the variety that is lowest in sugar per serving.

There are also some people who should avoid kombucha altogether for safety precautions. This includes pregnant women, young children, and those with compromised immune systems.

The bottom line.

Kombucha is a delicious, fizzy drink that can have many health benefits, and it's not shown to have adverse effects on healthy individuals. However, we still aren't certain of the potential health risks for those with preexisting health problems or people who drink the tea in excessive quantities, so if you fall into that group you might want to take precautions before you start sipping. 

If you're ready to reap the many benefits of this fermented tea, feel free to take a look at the many ways you can use kombucha to elevate your drink recipes. If you've got some time on your hands, you can even make your own booch!

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Isabel Smith, R.D., CDN author page.
Isabel Smith, R.D., CDN
Certified Dietitian and Nutritionist

Isabel Smith is a New York City-based dietitian, fitness expert, and founder of Isabel Smith Nutrition and Lifestyle. She received her B.A. in health and exercise sciences from Gettysburg College before a M.S. in nutrition communications at Tufts University. She also completed a dietetic internship and worked as an oncology fellow at New York Presbyterian Hospital. In her private practice, she works as a concierge nutritionist for both individual and corporate clients, including Fortune 500 corporations and their C-level executives. Smith has helped hundreds of people worldwide reach their nutrition, fitness, health, and wellness goals, and she also spends time writing and works as a nutrition consultant to a variety of health-minded brands.