A few years ago, you'd be hard pressed to find kombucha at the supermarket. These days, it seems to be everywhere.
A quick online search for kombucha — and similar drinks like switchel or water kefir — brings up all sorts of supposed benefits from reducing inflammation to weight loss.
But are these drinks all they're cracked up to be? And how do they compare to other drinks?
What evidence is there for health claims about kombucha?
Kombucha is a fermented tea drink that has been consumed by humans for more than 2,000 years.
It's made by fermenting tea with a "tea fungus" — also known as a SCOBY (symbiotic culture of bacteria and yeast).
Many commercial kombuchas have added sweeteners or fruit juice to improve the taste, but homemade versions often have a mild acidic taste.
There are many claims made about kombucha's health benefits, but there's not a lot of high-quality evidence to back that just yet.
That's the message from Evangeline Mantzioris, an accredited practising dietitian and program director of nutrition and food sciences at the University of South Australia.
"Most of the health claims about kombucha are based on in-vitro studies, which are done in the laboratory with cells," she says.
"Certainly some of those studies and some animal studies do show favourable health effects, but we cannot say that those health effects are relevant to humans yet, because we don't have the evidence."
What's in kombucha
Kombucha contains live bacteria in much the same way yoghurt or other fermented foods and drinks do, as well microorganisms from yeast.
Because it's made with tea, kombucha also contains polyphenols — organic plant-derived chemicals that have been linked to some positive health effects.
One thing to keep in mind is polyphenols aren't exclusive to kombucha. They're also in a cup of tea, a glass of wine and even chocolate.
But while research is still patchy, Senaka Ranadheera — a food scientist and lecturer at Melbourne University — says there could be some beneficial effects from the live cultures in kombucha.
"For instance, some of these microorganisms can create vitamin B1, B6, B12 and they are rich in vitamin C as well," he says.
What about sweeteners and sugar?
Most commercial kombucha drinks have low or no sugar. Instead, they often contain natural sweeteners like stevia.
In case you're wondering, natural sweeteners are safe to consume at the levels found in these drinks, according to Dr Ranadheera. There may be complications though at very large doses, he adds.
One positive is that they have a low energy content.
"Stevia, for instance, has a much lower calorie content than raw sugar," Dr Ranadheera says.
Sugar content comparison
Cola — 12.8g sugar per 100mL
Lemonade — 9.2g per 100mL
Store-bought kombucha or water kefir — 1-2.1g/100m
Sugar-free kombucha — 0g/100ml
Diet soft drink — 0g/100ml
Switchel — depends on sweetener used
Does it matter if kombucha is pasteurised?
One challenge for drink makers is kombucha's shelf life. If the drink contains sugar, it needs to be refrigerated otherwise it will continue to ferment.
To get around this problem, some brands bottle kombucha after all the sugar has been consumed by the fermentation process. This way, they can store it at room temperature without problems.
Others pasteurise their kombucha to extend its shelf life. The pasteurisation process stops the fermentation by killing the cultures. So keep in mind the drink won't contain live cultures.
What about switchel?
Another drink that's marketed for its health benefits is switchel, a combination of apple cider vinegar, ginger and sugar or other sweeteners.
Like kombucha, switchel is a traditional drink. It's thought to have originated in the Caribbean.
Many commercial varieties of switchel use natural sweeteners rather than sugar and are marketed as health drinks. But their health benefits haven't been well researched.
"There's almost nothing in the research literature on switchel. It's only mentioned in some articles as a traditional beverage, but I couldn't find any research articles," Dr Ranadheera says.
"However, the inclusion of apple cider vinegar in this product may have some potential benefits.
Small-scale human studies have linked apple cider vinegar to anti-diabetic effects and reduced cholesterol.
"Again, these benefits are sometimes a bit vague, and we need to do more research."
And you can get the potential benefits of apple cider vinegar by using it on your salad.
Water kefir
Another drink that is appearing more regularly alongside kombucha and switchel is water kefir, which is also sometimes known as tibicos.
It's a bit like kombucha, but without the tea. It's made by fermenting fruit-infused water with water kefir grains, a special type of SCOBY.
Again, there's hasn't been much research conducted on water kefir, so we can't draw any conclusions about its health benefits yet.
But Dr Ranadheera says the drink will have a similar profile to kombucha.
"I think kombucha and water kefir might have very similar sort of benefits, except the tea has more phenol content," he says.
"They both use SCOBY. The compositions are different but they both contain probiotic health effects."
The bottom line
"If people really like the taste of these drinks, or enjoy making them, there's no problem with drinking them. Just watch the sugar." — Dr Mantzioris.
"These drinks are likely going to be much better for you than soft drinks." — Dr Ranadheera.
Article from ABC Life