With this promise of probiotics, consumers are snapping up supplements and bacteria-enhanced beverages and snacks. According to a survey conducted by the National Center for Health Statistics, 3 million more U.S. adults used probiotics or prebiotics (a plant fiber) in 2012 than did so in 2007. The global probiotics market was over $35 billion in 2015, according to research from Global Market Insights.
However, the enthusiasm for these good-for-you bugs may be getting ahead of the research. Scientists are just beginning to understand the complex function of the microbiome, how probiotics work and the potential for targeted treatments.
"The field resembles the Wild West," says Claire Fraser, director of the Institute of Genome Sciences at the University of Maryland School of Medicine. Although there are some intriguing results pointing to the beneficial effects of probiotics, Fraser says, there needs to be additional studies before scientists can translate that information into clinical recommendations.
Also, the probiotic supplements on the market now might not be that helpful. It's not yet clear how to re-create a healthy or fully diverse microbiome, says Lee Kaplan, director of the Obesity, Metabolism and Nutrition Institute at Massachusetts General Hospital. "It's unlikely that the probiotics that are currently available will do that," Kaplan says. "We probably don't have the right ones yet."
A promising start
Russian scientist Elie Metchnikoff first observed more than 100 years ago that eating fermented foods may be associated with well-being and longevity. In the past 10 years, research has accelerated as scientists developed tools to study the microbiome in depth. Kaplan says researchers now know the microbiome can affect mood, bowel function, obesity, diabetes and inflammation.
But scientists don't yet understand how the microorganisms living in our gastrointestinal tract give rise to or affect these conditions, let alone how to fix an unhealthy gut.
Few well-designed human studies offer conclusive evidence that manipulating the gut's microorganisms can prevent or treat specific diseases, says Purna Kashyap, an assistant professor of medicine at the Mayo Clinic and a member of the scientific advisory board for the American Gastroenterological Association's Center for Gut Microbiome Research and Education.
So far, evidence supports the use of beneficial bacterial strains as targeted therapy in a few specific cases. For example, probiotics have been found to significantly reduce the incidence of necrotizing enterocolitis, a life-threatening gastrointestinal disease in preterm infants, and diarrhea caused by Clostridium difficile, an infection that may take root following antibiotic use.
Promising research shows that probiotics may help with other conditions, such as acute diarrhea, antibiotics-associated diarrhea in children, Helicobacter pylori infection (a bacterial ailment associated with peptic ulcers) and gastrointestinal disorders including irritable bowel syndrome. Other studies indicate that probiotics may help prevent acute upper respiratory tract infections and the common cold.
However, additional research and clinical trials are needed to evaluate the efficacy of specific strains of bacteria, or a combination of strains, to "alter both the composition of the microbiome in a given disease state and whether or not clinical symptoms associated with the disease are also relieved," Fraser says. This will help guide recommendations on dosage and who ultimately may benefit from probiotic treatment.
On the other hand, there's insufficient evidence that probiotics can help treat Crohn's disease, eczema, urinary tract infections, periodontal disease or allergies.
Should you take probiotics?
Scientists and physicians are optimistic about the future of "good" microbes. Many probiotic and microbial-based compounds are moving to the next stages of research and clinical trials. Researchers hope this will illuminate how gut microorganisms interact with specific diseases and medical conditions, yielding more-targeted and therapeutic probiotics. "We'll see a new wave of probiotics coming out that can be used to treat disease" in the coming years, Kashyap predicts.
Until then, it's anyone's guess whether taking a daily dose of bacteria will help you.
Because probiotics are sold as food and dietary supplements, they aren't subject to the same regulation that the Food and Drug Administration exercises over drugs. (Supplements don't have to prove their effectiveness before being sold, though the FDA can intervene if problems are found once they are sold.) That means the products may not actually contain live bacteria or even the type and number of bacterial strains promised on the packaging.
"There's no way to confirm what is listed on the box is what is in the box, that it's safe and useful, and that it will help you," Kashyap says. For example, an examination of 16 probiotic products in 2015 found that only one contained the bacterial strain listed on the label of every tested sample.
"Right now, we can't predict who's going to feel better and who's not," Kashyap says. Some people don't feel any different when taking the supplement, while others say it's made them healthier.
Take Sue Tate, for example. The 40-year-old pediatric intensive care nurse from Alexandria said she would experience a bad upper respiratory infection three or four times a year. Since she began taking a daily probiotic, she is rarely sick. Tate admits it's hard to tell if the supplement alone is responsible for her improved condition or if it's a combination of other factors. It's also possible there's a placebo effect at work too: If someone thinks they're taking something beneficial, they sometimes feel better. But she's sticking with her routine for now.
"If you feel better, you can continue taking them," Kashyap says. Most probiotics are inexpensive, don't require a prescription and aren't likely to cause harm. But in general, he recommends holding off until the next generation of probiotics comes to market. In particular, if you have an immune deficiency or are sick, definitely steer clear. "Even healthy bacteria can be dangerous in these people," he says.
If you want to nourish your gut, your best bet is to eat a healthy diet — a variety of vegetables, fruit and fiber. You can also include probiotic-rich food such as yogurt, kefir and miso. And, because antibiotics can wipe out the good bacteria in your microbiome along with the bad, those drugs should be used only when medically necessary.