Kombucha, probiotic or gimmick

A look at human studies and what the science says

Kombucha is so popular at this point that there is no stopping it. Every bottle of kombucha made in the USA today definitely has a printed designation that it is in fact probiotic. However, as I have posted before, the term probiotic must be used to refer to a food or beverage that contains “Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” - (Check out the ISAPP website for more info!) The question is: are there proven health benefits for the microbes ingested when drinking this fizzy, sour beverage for the host, eg. humans.

What is kombucha: Fermented teas (generally black, green, or oolong) that contain a myriad of microbes of both prokaryotes (bacteria) and eukaryotes (yeasts). By adding sugar to the teas along with microbes we can induce fermentation and drop the pH of the solution, creating the characteristic vinegar flavor of kombucha (basically just acetic acid). Many commercial kombuchas also contain added sugars post-fermentation (up to 20-30 g per serving), which would essentially negate any health benefits in the first place.

The microbes found in kombucha are known collectively as the mother, or more scientifically the SCOBY (symbiotic culture of bacteria and yeast). The SCOBY can be comprised of bacteria species such as Acetobacter xylinum, Acetobacter aceti, Acetobacter pasteurianus, and Gluconobacter oxydans, and yeast species such as Saccharomyces sp., Zygosaccharomyces kombuchaensis, Torulopsis sp., Pichia spp., Brettanomyces sp. and Zygosaccharomyces bailii. Notably, kombuchas don’t usually contain a large contingent of lactic acid bacteria, unless they are added in post-fermentation. Adding in these bacteria post-fermentation is a way that these beverages could be designated as probiotic, (as long as the microbes have been studied and shown to have real health benefits in humans!)

After fermentation kombucha is a cocktail of molecules including sugars, polyphenols, organic food acids (acetic being the main acid), ethanol and water-soluble vitamins such as vitamin C and B. While some of these components on their own may have known health benefits (antioxidant effects of vitamin C and polyphenols), the question remains: do the microbes in kombucha confer a health benefit to homo sapiens?

It turns out that biological activities of drinking kombucha have been studied in rats, mice, rabbits, ducks, dogs, pigs, cattle, broiler chickens, and human white blood cells (Old McDonald screaming: eee i eee i ooooo). Unfortunately, there have been no controlled human studies looking at health benefits in humans. In each of the animal studies, the reported health benefits have been attributed to the fermentation products present in the beverage and not from ingesting the microbes. Therefore kombucha as it is traditionally brewed and fermented can not be labeled as probiotic. There would need to be some human data available on the benefits of ingesting at least one of the microbes present.

So all in all kombucha may be a healthy drink, but so is regular old tea. Are there really health benefits for drinking fermented tea versus drinking normal tea? We may never know. We should know, because it would actually be a really easy study to do. How would we do it: Take a group of random semi-healthy adults and measure their health (blood pressure, blood glucose, or bowl movement frequency) before the experiment, then give half of them tea every day, and the other half fermented tea every day. If we look at something basic like blood pressure, or blood glucose we may be able to see a difference in the groups between these two beverages. We could then repeat the study with new volunteers, except this time half of the group would get fermented tea, and the other group would drink fermented tea that has been filtered to remove the microbes. This would tell us if any health benefits we saw were attributed to the fermentation products or the microbes themselves.

In the end, consumers are usually paying a premium for the probiotic label without knowing what it all really means. Hope this post can clear up a bit of that confusion.