What’s the Skinny on Kombucha?

Did you ever wonder if the food you eat has a direct effect on your health, well-being – and longevity?  Well, I’m here to end that mystery.  You ARE the foods you eat.  Welcome to the Nutrition Facts podcast – I’m your host, Dr. Michael Greger.

Today we take a slug of Kombucha.  And wonder… what are the risks versus benefits of doing such a thing?

My video on kombucha profiled a report published in the Journal of Intensive Care Medicine of a case of kombucha tea toxicity. A young guy ending up in an acidotic coma, which concluded that “[w]hile Kombucha tea is considered a healthy elixir, the limited evidence currently available raises considerable concern that it may pose serious health risks. Consumption of this tea should be discouraged, as it may be associated with life-threatening lactic acidosis.” And this was just one of several case reports of serious, and sometimes fatal, liver dysfunction and lactic acidosis within close proximity of ingestion.

For example, two cases in Iowa of severe metabolic acidosis including one death: the triggering of a life-threatening autoimmune muscle disease requiring emergency surgery, probably related to kombucha; shaking, shortness of breath, and a movement disorder after consumption of tea and no other medications; xerostomia, dizziness, nausea, vomiting, headache, and neck pain, which recurred on reingestion of the tea. Then, another case of severe metabolic lactic acidosis and a case of hepatotoxicity—liver toxicity—that resolved after stopping kombucha.

Why these sporadic cases? Maybe some unusual toxins developed in a particular batch. I mean it is a fermented product; so, it’s possible it was just contaminated by some bad bug. Like the time people smeared kombucha on their skin because they were told it had magical healing power. What it instead had was anthrax growing in it. So, even though such reports were rare, ten years ago I concluded maybe we should stick to foods that haven’t put people in a coma. But look, everything in life is all about risks versus benefits. Maybe it’s worth it. After all, it’s reputed to cure cancer, eliminate wrinkles, and even restore gray hair to its original color, marketed by alternative and naturopathic healers throughout the United States.

Currently, kombucha is praised as “the ultimate health drink” or damned as “unsafe,” claimed to be a universal wonderful drug, known as a purifying potion. But is it a potion or poison?

Evidently, back in the 20s, 30s, and 40s, there were several medical studies conducted by recognized physicians confirming all sorts of beneficial effects. I couldn’t wait to read them. Okay, so, they cite Dufrense and Farnworth. Okay, there it is, same claim, citing Allen. Okay what’s Allen, 1998? Oh, you’ve got to be kidding me. You’re citing some rando kombucha website. And here it is, defunct since 2001, sourced citationless from stuff that was posted on some mailing list.

Finally, in 2003, a systematic review of the clinical evidence that was published, and the main result of this systematic review was “the total lack of efficacy data.” No clinical studies were found. We just have these cautionary tale case reports. So, on the basis of these data, it was concluded that the largely undetermined benefits do not outweigh the documented risks of kombucha. It can, therefore, not be recommended. Okay, but that was back in 2003. How about a 2019 systematic review of the empirical evidence of human health benefit?

The “nonhuman” subjects literature claims numerous health benefits of kombucha, meaning mice and rats, but what we need are human clinical trials. And still, not a single controlled human study. But they did find one uncontrolled study showing a significant before-and-after reduction in fasting and after-a-meal blood sugars among type 2 diabetics. Nonetheless, despite no controlled trials, significant commercial shelf space is now dedicated to kombucha products, and there is widespread belief that the products promote health. So, we’re left with this extreme disparity between science and belief, with little convincing clinical evidence, yet health claims that are as far-reaching as they are implausible, while the potential for harm seems considerable. In such extreme cases, healthcare professionals should discourage consumers from using (and paying for) anything that only seems to benefit those who sell it.

In our next story, we look at some scary reports of people ending up in a coma after drinking Kombucha.

Tea is healthy; mushrooms are healthy. What if you put them together? Kombucha tea, a fizzy fermented drink—complete with chunks of slimy fungus.

Now, if you base your nutrition knowledge on the kinds of books you find in health food stores, bestsellers like Kombucha—The Magical Fungus will tell you that already by the Tsin dynasty, it was known and honored as a beverage with magical powers, enabling people to live forever. Given the fact that you don’t tend to meet many people from the Tsin dynasty these days, not only may kombucha not give you eternal life—it apparently won’t even grant you a measly 2,000 years. Never believe anything you read in health food stores.

But what does the science say? Kombucha tea—harmful, just harmless, or helpful? Kombucha tea can be harmful. Published last year in the Journal of Intensive Care Medicine, kombucha “may pose serious health risks. Consumption of this tea should be discouraged, as it may be associated with life-threatening lactic acidosis.”

This is just the latest in a series of case reports of people ending up in a coma because their blood turned to acid after drinking kombucha. How does it do that? We have no idea. Maybe it’s a magical fungus after all.

Finally today – we’ve got a timely review on the health effects of tea, coffee, milk, wine, and soda.

One phrase you’ll hear repeatedly in my videos and books is “best available balance of evidence.” What does that mean? When making decisions as life-or-death important as to what to best feed ourselves and our families, it matters less what a single study says, but rather what the totality of peer-reviewed science has to say.

To know if there’s really a link between second-hand smoke and lung cancer, it would be better to look at a review or meta-analysis that compiles multiple studies together. The problem is that some reviews say one thing––breathing other people’s tobacco smoke is a cause of lung cancer—and some reviews say another, saying the effects of second-hand smoke are insignificant, and further, such talk may foster “irrational” fears. And, hey, while we’re at it, you can even directly smoke four or five cigarettes a day and not really worry about it; so, light up.

Why do review articles on the health effects reach such different conclusions? Well, as you can imagine, about 90% of reviews written by tobacco industry-affiliated researchers said it was not harmful, whereas you get the opposite number with independent reviews. Reviews written by tobacco researchers had 88 times the odds of concluding second-hand smoke was harmless. It was all part of a deliberate corporate strategy to discredit the science––to, in their words, develop and widely publicize evidence that second-hand smoke is harmless.

Okay, well, can’t you just stick to the independent reviews? The problem is that industry-funded researchers have all sorts of sneaky ways to get out of declaring conflicts of interest. So, it’s hard to follow the money. But, even without knowing who funded what, the majority of reviews still concluded second-hand smoke was harmful. So, just like a single study may not be as helpful as looking at a compilation of studies on a topic, a single review may not be as useful as a compilation of reviews. So, looking at a review of reviews can give you a better sense of where the best available balance of evidence may lie. In this case, it’s probably best not to inhale.

Wouldn’t it be cool if there were reviews-of-reviews for different foods? Voilà! An exhaustive review of meta-analyses and systematic reviews on the associations between food and beverage groups and major diet-related chronic diseases. Let’s start with the beverages. The findings were classified into three categories: protective, neutral, or deleterious. First up: tea versus coffee. In both cases, most reviews, for whichever condition they were studying, found both beverages to be protective. But you can see how this supports my recommendation for tea over coffee. Every cup of coffee is a lost opportunity to drink something even healthier: a cup of green tea.

No surprise, soda sinks to the bottom. But still, 14% of reviews mentioned protective effects of drinking soda!? Well, most were references to papers like this: a cross-sectional study that found that 8^th grade girls who drank more soda were skinnier than girls who drank less. Okay, but this was just a snapshot in time. What do you think is more likely, that the fatter girls were heavier because they drank less soda, or that they drank less sugary soda because they were heavier? Soda abstention may therefore be a consequence of obesity, rather than a cause, yet it gets marked down as protective; there’s a protective association.

Study design flaws may also account for these wine numbers. This review of reviews was published back in 2014, before the revolution in our understanding of the evaporating health benefits of alcohol, suggesting that the presumed health benefits from “moderate” alcohol may have finally collapsed, thanks, in part, to a systematic error of misclassifying former drinkers as if they were lifelong abstainers. Sometimes there are unexplainable associations, though. For example, one of the soft drink studies found that increased soda consumption was associated with lower risk of certain types of esophageal cancers.

Don’t tell me—the review was funded by, Coca-Cola? The review was funded by, Coca-Cola! Does that help explain these positive milk studies? Were they all just funded by the dairy council? Even more conflicts of interest have been found among milk studies than soda studies, with industry-funded studies of all such beverages approximately “four to eight times more likely to be favorable to the financial interests of the [study] sponsor….”

Funding bias aside, though, there could be legitimate reasons for the protective effects associated with milk consumption. After all, those who drink more milk as a beverage may drink less soda, which is even worse; so, they come out ahead. But it may be more than just relative benefits. The soda-cancer link seems a little tenuous, not just because of the coke connection, but it’s hard to imagine a biologically plausible mechanism, whereas even something as universally condemned as tobacco isn’t universally bad. As I’ve explored before, more than 50 studies have consistently found a protective association with Parkinson’s, thanks to nicotine. Even second-hand smoke may be protective. Of course, you’d still want to avoid it. It may decrease the risk of Parkinson’s, but increases the risk of an even deadlier brain disease: stroke, not to mention lung cancer and heart disease, which has killed off millions of Americans since the first Surgeon General’s report was released.

Thankfully, by eating certain vegetables, we may be able to get some of the benefits without the risks, and the same may be true of dairy. As I’ve described before, the consumption of milk is associated with increased risk of prostate cancer, leading to recommendations suggesting men may want to cut down or minimize their intake. But milk consumption is associated with decreased colorectal cancer risk. This appears to be a calcium effect. Thankfully, we may be able to get the best of both worlds by eating high-calcium plant foods, such as greens and beans.

We would love it if you could share with us your stories about reinventing your health through evidence-based nutrition.  Go to nutrition facts.org slash testimonials. We may share it on our social media to help inspire others.

To see any graphs charts, graphics, images or studies mentioned here, please go to the Nutrition Facts podcast landing page.  There you’ll find all the detailed information you need – plus links to all of the sources we cite for each of these topics.

For a vital, timely text on the pathogens that cause pandemics – you can order the E-book, audio book, or the hard copy of my latest book “How to Survive a Pandemic.”

For recipes, check out my new “How Not to Diet Cookbook.” It’s beautifully designed, with more than 100 recipes for delicious and nutritious, meals.  And all proceeds I receive from the sales of my books go to charity.

NutritionFacts.org is a nonprofit, science-based public service, where you can sign up for free daily updates on the latest in nutrition research via bite-sized videos and articles.

Everything on the website is free. There’s no ads, no corporate sponsorship.  It’s strictly non-commercial.  I’m not selling anything. I just put it up as a public service, as a labor of love – as a tribute to my grandmother – whose own life was saved with evidence-based nutrition.