Probiotic supplements may do the opposite of boosting your gut health

Probiotic supplements have grown into a multibillion-dollar industry, spurred by claims that the products will populate your gut with bacteria that can boost your health in numerous ways.

But beware of the hype: In healthy people, probiotic supplements offer little benefit, and they can potentially do more harm than good.

Studies show that taking probiotic supplements — for overall health or to counter the effects of antibiotics — can alter the composition of your microbiome and reduce the levels of microbial diversity in your gut, which is linked to a number of health problems.

Probiotic supplements come in the form of capsules, gummies, powders and pills that contain live microorganisms believed to boost gut health. There is a subset of people who may benefit from taking them, including people with gastrointestinal ailments. Studies have found that probiotic supplements can reduce symptoms of irritable bowel syndrome and inflammatory bowel disease. They can prevent traveler's diarrhea and reduce some side effects of antibiotic medications.

But for most people, more reliable ways are available to nourish your gut microbiome.

First, eat a variety of vegetables, nuts, seeds, beans and whole grains, which provide gut microbes the fiber-rich fuel that they need to thrive. Researchers have found that eating fermented foods such as yogurt, sauerkraut, kimchi and kefir, which contain probiotics and other beneficial compounds, have positive effects on your health and gut microbiome.

Your gut microbes are part of a vast ecosystem of bacteria, viruses, archaea and fungi located largely in your colon. People who harbor diverse gut microbiomes tend to age more healthfully and develop fewer diseases.

These microbes thrive on the fiber found in fruits and vegetables, turning it into new compounds or "postbiotics," including butyrate, acetate and other short-chain fatty acids that appear to be exceptionally good for your health.

But like residents of any community, the microbes in your gut can work together and compete against one another. Sometimes the proportion of good and bad bacteria in your gut can get out of balance — a condition known as dysbiosis.

Although there are numerous brands of probiotic supplements, many of them contain a limited number of bacterial strains, primarily from the groups lactobacillus, bifidobacterium and a few others. These microorganisms are quite common and have been associated with many health benefits.

But taking concentrated doses of a few strains of bacteria can upset the balance in your gut, said Lorenzo Cohen, a professor and director of the Integrative Medicine Program at the University of Texas MD Anderson Cancer Center in Houston.

"You can inadvertently create a form of dysbiosis by having too much of a good thing," he said. "You're not only crowding out the bad things, but crowding out the other good things that you want in there to create high microbiome diversity."

It's common for people to take probiotics alongside antibiotic medications. Antibiotics treat bacterial infections, but they can also wipe out beneficial bacteria. The idea behind taking a probiotic supplement with an antibiotic is to rebalance the gut microbiome and minimize side effects. Studies have shown, for example, that probiotics can prevent antibiotic-associated diarrhea.

But one study of probiotic use with antibiotics produced surprising results. Researchers at the Weizmann Institute of Science recruited healthy adults and gave them a weeklong course of antibiotics.

Then one group took a popular probiotic supplement for four weeks that contained at least 10 species of bacteria. Another group received stool transplants containing their own gut microbes, which were collected before the antibiotics were administered. A third group served as the control.

The microbiomes of people in the control group returned to normal about three weeks after taking the antibiotics. The microbiomes of people who received the stool transplants after the antibiotic treatment fared the best, returning to normal within days.

But the microbiomes of people who took the probiotics had not returned to normal even after five months. The scientists found that they also had less gut microbiome diversity compared to people in the control or transplant groups.

In another recent clinical trial, scientists at Stanford recruited adults with metabolic syndrome — a combination of risk factors for Type 2 diabetes, such as abdominal obesity, high blood pressure and high triglycerides — and then split them into two groups. One was given a probiotic containing several strains of bacteria thought to be good for metabolic and digestive health. The second group did not take probiotics and served as the controls.

After 18 weeks, the scientists found that some people taking the probiotic supplement had improvements in their blood pressure and triglyceride levels. But others in the probiotic group showed a worsening of their blood sugar and insulin levels.

The researchers say that differences in diet could have played a role in the results, but it's not clear. The findings underscore that probiotic supplements can have very different effects in different people, said Erica Sonnenburg, an author of the study and senior research scientist in microbiology and immunology at Stanford.

"It's a common theme," she added. "Probiotics can be beneficial for some individuals. But it also seems that for some individuals they can make things worse."

So what should you do? If you've been prescribed an antibiotic, or you have a digestive ailment, you should talk to your doctor about whether it makes sense for you to take a probiotic supplement — and if so, which brand or product. You may be advised to skip probiotics altogether if you have a severe illness or compromised immune system because of the risk of developing an infection.

Some doctors might recommend adding fermented foods to your diet instead of taking a supplement. "When I do recommend live microbes, it's often in the context of fermented foods," said Chris Damman, a gastroenterologist at the Digestive Health Center at the University of Washington Medical Center. "Fermented foods are like nature's probiotics."

One of the benefits of fermented foods is that they typically contain not just probiotics (the live microbes) but also prebiotics (the fiber the microbes eat) and postbiotics (the vitamins and other nutrients they produce). In a study published in the journal Cell, Sonnenburg and her colleagues at Stanford found that assigning people to eat fermented foods every day over a 10-week period lowered their levels of inflammation and increased their gut microbiome diversity.

If you're new to fermented foods, Damman recommended introducing them gradually.

Try using sauerkraut or kimchi as a garnish with your meals. Have a bowl of plain yogurt for breakfast. Drink a cup of unsweetened kefir as a snack or use it to make a fruit smoothie.

"I don't take a probiotic, but I do eat a variety of fermented foods — and that's generally the advice that I give people," Damman said.