Slightly sweet, somewhat bubbly and always tangy, kombucha is a fermented tea drink whose supposed healing powers have been touted for centuries.

Civilizations throughout history and across the world have turned to kombucha based on the belief it could boost immunity, digestion and metabolism, revitalize and re-energize mind and body, promote a healthy heart and even ward off cancer.

Today, kombucha is still considered a wellness drink, stocked by supermarkets near the health food aisle.

But — whether you drink kombucha for the health claims or just because you like the taste — what does the science actually say about the benefits of kombucha?

What do we really know about the health benefits of kombucha?

Understanding why kombucha might be good for you starts with understanding how it's made.

You've likely heard of a sourdough starter by now, but probably less likely to have heard of a SCOBY.

SCOBY stands for "Symbiotic Culture Of Bacteria and Yeast" and it's what turns regular old tea into fermented tea — that is, kombucha.

Kombucha is made by combining three main ingredients:

• Black tea (also sometimes green, oolong or herbal tea varieties)
• Sugar
• A colony of live bacteria and yeast (the SCOBY)
  
  

Once mixed together, the SCOBY gets to work fermenting the sweet tea mixture. Over the course of a few weeks to a month or more, the microbes work together to break sugar down into alcohol and organic acids. Some carbonation is also produced.

Eventually, the mixture becomes kombucha — a fizzy tea drink containing:

• Organic acids (think vinegar)
• Probiotics (live, beneficial bacteria and yeasts)
• Antioxidants
• B vitamins
• Small amounts of alcohol and caffeine
  
  

Most of the familiar, tangy taste of kombucha comes from the organic acids, but it's the probiotics and antioxidants that are thought to pack in the health benefits.

But, unfortunately...the numerous health claims attributed to kombucha aren't actually supported by scientific research.

While a handful of studies has looked at the benefits of kombucha, only one has ever analyzed its impact in people — and it lacked a control group, making the results limited. All other studies have relied on animal research models, so any benefits reported in them may or may not actually translate to humans.

Ultimately, kombucha's health benefits must be tested in human trials before its claims can be accepted by science.

That being said, there's nothing to suggest kombucha is unhealthy for most people when consumed in moderation. One thing to keep in mind is that kombucha contains sugar — usually more than two grams per eight fluid ounces, at the very least. Additionally, the low pH of kombucha could have negative implications for your tooth enamel.

Do the probiotics in kombucha boost your gut health?

Probiotics are beneficial microbes that may help prevent and/or treat a variety of health conditions, such as antibiotic-associated diarrhea and ulcerative colitis.

However, the FDA has not approved any probiotics and many questions remain regarding them, including which are most helpful, what amount likely promotes better health and who benefits most?

So, while kombucha does contain live, beneficial bacteria and yeast, whether these microbes actually do anything for you remains to be seen.

What's more is that the probiotic composition of kombucha can vary significantly, meaning it may be hard for kombucha manufacturers to ever truly know how their product, specifically, may impact a person's health.

Can the antioxidants in kombucha benefit your health?

Antioxidants are compounds that can help protect your body from "free radical" damage — damage that happens naturally over time, as well as a result of certain lifestyle behaviors.

Tea itself is known for its antioxidant and anti-inflammatory power, likely due to the polyphenols it contains. Observational studies have shown that people who regularly drink tea have a lower risk of heart disease and diabetes, although the exact mechanism by which tea contributes to these health outcomes is still largely unclear.

As a fermented tea drink, it stands to reason that kombucha might hold some of the same benefits we know to be true for unfermented tea. However, it's important to note that tea's known health benefits apply to those who drink several cups per day.

It's not advised that people drink as much kombucha, given its sugar content. It's unknown if, say, a single cup day would provide any health benefits.

Can kombucha ever be bad for you?

According to the CDC, it's safe to consume four ounces of kombucha three times per day. The safety of drinking more than this is unknown.

If you're new to drinking kombucha, you may want to start slow since the low pH of this beverage might contribute to some GI distress.

In addition, since kombucha is not pasteurized, some people should avoid drinking kombucha altogether, such as those who are higher risk for foodborne illness, including:

• Women who are pregnant
• People with a weakened immune system
  
  

Pregnant women still considering drinking kombucha should also be aware that it contains both alcohol and caffeine (although usually in small amounts).

Lastly, be cautious about home-brewed kombucha — especially if the brewer is new to fermentation. Inadequate sanitation of brewing equipment can lead to contamination with harmful bacteria, and fermenting in improper vessels, such as clay jars, can lead to harmful compounds leaching into the beverage.