This story is a part of The Elemental Guide to Vitamins. Here are the vitamins and supplements that are covered: multivitamins, vitamin D, vitamin C, calcium, B vitamins, omega-3, vitamin E, fiber, protein, and probiotics.
The human gut is filled with trillions of bacteria that are known collectively as the microbiome. And these microorganisms seem to play a crucial role in human health.
During the past 20 years, studies have repeatedly found that the microbiomes of sick people tend to differ from those of well people and that this is true even for people with brain diseases like dementia. In some cases — such as for people who have a type of recurring bacterial infection called Clostridium difficile (C. diff) — introducing healthy bacteria into a person’s microbiome using procedures like fecal transplants can help treat the condition.
The foods a person eats can change the makeup of their microbiome for better or worse. This realization has led to an explosion in the market for probiotics, which are foods or supplements that encourage the growth of healthy gut bacteria. By increasing the types or amounts of certain bacteria and discouraging the growth of others, probiotics may prevent or treat a wide range of medical conditions. At least, that’s the idea.
This idea is not far-fetched. Some studies have found that some probiotic formulations, namely a patented cocktail called VSL#3, can reduce symptoms in people who have ulcerative colitis, which is a form of inflammatory bowel disease. But for most medical conditions — and also for healthy people who are looking to prevent disease — the evidence backing probiotic supplements is meager.
While pumping the gut full of healthy bacteria is helpful for treating some specific medical conditions, it’s probably not the cure-all that probiotic manufacturers have led people to believe.
“The business of probiotics has outpaced the science,” says Dr. Emeran Mayer, co-director of the Digestive Diseases Research Center at UCLA and author of The Mind-Gut Connection. Mayer says the idea that people can swallow a probiotic pill and re-shape the makeup of their gut bacteria in health-promoting ways has not been borne out in clinical trials. While some people do seem to experience benefits, these benefits aren’t consistent, and probiotics often don’t outperform placebo pills, he says. In some cases, people have reported side effects like an upset stomach or diarrhea in response to probiotics. In general, everyone’s microbiome makeup is different, and it’s tough to determine what bacterial balance they need.
Mayer is quick to add that these sorts of adverse reactions are uncommon and that probiotics seem to be safe for most people. But he says he often steers his patients away from supplements and toward foods that naturally contain probiotic bacteria — things like kefir, kimchi, and yogurt. For centuries, people around the world have eaten these foods and associated them with improved health, and there’s no evidence that they pose serious risks, he says.
Others who have examined the research on probiotics and the microbiome say people may have it backward when they assume that changing their gut bacteria will improve their health. “As people become healthier, the gut adapts,” says Dr. Mark Moyad, the Jenkins/Pokempner director of preventive and alternative medicine at the University of Michigan.
He points out that when people lose weight or exercise, their microbiomes become healthier. And so it may be that the microbiome is a marker of a person’s overall health rather than the driving force. While pumping the gut full of certain types of healthy bacteria is helpful for treating some specific medical conditions — such as C. diff infections — it’s probably not the cure-all that probiotic manufacturers have led people to believe.
“There’s this question of how much is cause and how much is consequence,” Moyad says. “There’s a lot about probiotics that people should be excited about, but there’s still a lot we don’t understand.” He mentions a 2018 study in the journal Cell that found probiotics actually interfered with the regrowth of healthy bacteria in people who had taken antibiotics. While this doesn’t suggest probiotics are dangerous, it does reveal that they could come with some unexpected downsides, he says. Like Mayer, he recommends that people get their probiotics from foods that naturally contain healthy bacteria.
The bottom line: While it’s possible some people may benefit from a probiotic supplement, the science backing them is shaky, and they may even come with some risk. Talk to your doctor to see if you’re the right candidate.
This story is a part of The Elemental Guide to Vitamins.