Probiotics are everywhere. Walk in your local mega-mart, and it’s hard to miss the products offering you an extra dose of beneficial microbes.
In the past few years, the number of scientific articles published on the effects of probiotics on everything from cancer to anxiety has jumped from 175 in 2000 to a whopping 1,281 in 2013. These studies have already begun to show that certain types of probiotics are an effective treatment for some specific conditions.
But there’s a problem. Scientists say that the hype has far outstripped evidence supported by rigorous, peer-reviewed research studies. Guidance from the FDA isn’t clear, either. What consumers are left with, then, is a confusing array of products that may or may not be able to do what they claim. When it comes to probiotics, scientists say, what we still don’t know far overshadows what we do.
Although the FDA hasn’t yet formally defined the term “probiotic,” the World Health Organization (WHO) defines it as “live micro-organisms which, when administered in adequate amounts, confer a health beneﬁt on the host.” It’s the working definition scientists use as well. And although many studies testing the potential benefits of bacterial species to treat a condition may refer to these microbes as “probiotics,” it’s often a misnomer.
“Anyone who has a fermented anything says it has probiotics, which isn’t exactly true. It does appear that eating a variety of fermented foods like yogurt and kimchi is probably good for your health, that doesn’t mean these products contain bacteria we can call probiotic,” David Mills, a food microbiologist at the University of California, Davis, told The Daily Beast.
Establishing consistent evidence about the benefits of specific strains of bacteria has been difficult, because nearly every study evaluating probiotics uses different bacteria. It’s easy to think that most bacteria are nearly identical. Between their small size and similarity under the microscope, potentially beneficial bacteria all get grouped together in the human psyche, says Lynne McFarland, a microbiologist at the University of Washington. But this is pretty much the opposite of what we are learning about prokaryotic diversity.
Bacteria are equally as genetically diverse as the plants, animals, and fungi with which we are more familiar, even if they look remarkably similar.
The differences between paramecium, redwoods, and blue whales are easy to spot. In fact, it would be nearly impossible to confuse these three species. Yet bacteria are equally as genetically diverse as the plants, animals, and fungi with which we are more familiar, even if they look remarkably similar. One type of bacterium is likely very different from its neighbors, and may have equally different effects on the body.
Researchers have made the most progress in identifying beneficial microbes to help treat nectrotizing enterocolitis (NEC) in preterm infants. NEC is the most common and serious gastrointestinal disease affecting babies born prematurely, and involves the death of intestinal tissue. In severe cases, a hole develops in the intestines that can allow bacteria from the infant’s gut to leak into the body, causing sepsis. Scientists still aren’t sure exactly what causes NEC, but are working to develop ways to prevent its onset. Besides making sure that the infant remains properly fed and hydrated, scientists have begun administering various strains of probiotics to premature infants in some countries. In a 2014 review article (PDF), researchers concluded that the administration of “live microbial supplements” prevented severe forms of NEC and decreased the likelihood of death.
Close behind NEC in terms of evidence for efficacy is the use of helpful bacteria to replace those killed off by antibiotics, which can lead to diarrhea. Pediatric gastroenterologist David Allen at the University of Cardiff in Wales remains somewhat cautious about the data, saying it “looks promising,” but he doesn’t yet feel he can tell his patients which type of bacteria to take. McFarland says that taking a probiotic with an antibiotic should be standard treatment, but emphasizes the importance of taking the right strain.
“I was at the pharmacy, picking up some antibiotics, and the pharmacist told me, ‘Oh, be sure to take probiotics with this.’ She should have never opened her mouth,” McFarland laughs. “I immediately asked what kinds were effective, and she replied to ‘Just eat some yogurt.’” Although yogurts generally have “live and active cultures,” they don’t necessarily have probiotics, nor do they usually have enough of them to totally override the digestive disruption of antibiotics. After selecting the right strain, selecting the right dose is McFarland’s other major rule for taking probiotics, and it can be just as problematic as selecting the correct strain.
This hasn’t stopped food manufacturers from hyping health claims on their packaging, however. Many of these assertions are deliberately vague, claiming to “support gut health” or “support a healthy immune system.” Both of which may be true, Allen points out, but we can’t actually support that with specific research. “These products will say ‘supports a healthy gut flora.’ But we don’t even know what a healthy gut flora is,” he says.
The FDA doesn’t have an official definition for “probiotic,” nor does it regulate the use of the term, FDA spokeswoman Jennifer Dooren tells The Daily Beast. “To date, FDA has not approved health claims or qualified health claims for probiotics in conventional foods or dietary supplements,” she notes.
In 2010, Danone Incorporated (makers of Dannon yogurt, including the popular Activia brand that has added strains of potentially beneficial bacteria) settled a class action lawsuit for overstating the claims on its yogurt labels. Danone claimed that Activia yogurt “helps naturally regulate your digestive system,” and that DanActive yogurt “has been clinically proven to help naturally strengthen the body’s defenses when consumed daily.” The lawsuit alleged that Danone used these claims to bilk consumers out of more than $100 million. The company agreed to a $45 million payout to consumers and a “corrective advertising campaign” that toned down the health claims, telling consumers that they would need to eat at least three yogurts each day to see any potential health benefits. Even for a diehard yogurt lover, that’s a lot of yogurt.
Many consumers turn to these products not just to treat various health woes but to try to prevent them from starting in the first place. Just as people take a daily multivitamin to help prevent disease (research shows you probably don’t need one if you’re generally healthy), they have begun to dose themselves with bacteria that might also make them healthier. To which McFarland says, save your money.
“It’s probably a waste of time to take them every day. Your normal gut flora will fight off the probiotics,” McFarland said.
The chances that probiotics in food or taken as supplements are likely to cause harm is pretty small, but that doesn’t mean it’s zero. Allen says that some strains of bacteria may be potentially beneficial for some people but harmful to others. They also have the ability to pick up antibiotic resistance genes, which could also lead to potential problems down the road, according to a 2013 paper in Frontiers in Microbiology.
Scientists remain confident that some strains of bacteria will provide health benefits in some situations, but research still needs to sort out which strains for which people in which circumstances. “This field holds much promise. I really do think that ways of modulating gut health, through diet or probiotics, is something that’s going to be much more personalized in the future,” Mills says.
Until that future is here, however, “Eat yogurt for the strawberries, not the bacteria,” McFarland says.