Why Probiotics May Not Always Help, And Could Actually Do Harm?

January 22, 2021

Many people take probiotics in their food or supplements in hopes of boosting their digestive health. But a new small study suggests that some people may not benefit as much as others from these so-called good bacteria.

The study found that when people consumed standard strains of probiotics, some people’s stomachs developed resistance to the bacteria, meaning that the bacteria failed to successfully live in or colonize their gut. But for others, the bacteria easily grew and proliferated in the gut.

The researchers said the study suggests that not everyone may benefit equally from standard probiotic treatment.

“This suggests that probiotics should not be given universally as a ‘one-size-fits-all’ supplement,” study co-lead author Eran Elinav, an immunologist at the Weizmann Institute of Science in Israel, said in a statement. However, it may be that tailoring probiotic treatment to an individual, based on the type of microbes already in his or her gut, as well as other factors, allows him or her to get the most benefit from the probiotic, the researchers said.

In addition, a second study by the same group of researchers suggests that probiotics could have potentially harmful effects if taken after antibiotics. However, because both studies were small, more research is needed to confirm these findings.

Probiotic Bacteria “Drug-Resistant”
According to the Mayo Clinic, probiotics are live bacteria consumed for the purpose of improving or maintaining the microbiome or the many “good” bacteria found naturally in our gut.

There are many probiotic products on the market, including yogurt containing probiotics, as well as supplements and skin creams, with an estimated 3.9 million Americans using such products. Some studies suggest that probiotics may help with symptoms of diarrhea or irritable bowel syndrome (IBS), but the strong evidence supporting their use for most health conditions is lacking, according to the National Center for Complementary and Integrative Health.

In addition, most studies that have looked at the effects of probiotics have used participants’ stool samples as a proxy for what’s in their gut. But it’s unclear whether the fecal samples actually reflected the bacteria living in the gut, or whether some of the bacteria were more likely to shed in the feces and perhaps didn’t settle properly in the gut.

In the new study, researchers analyzed information from 15 healthy volunteers who took a probiotic product or placebo containing 11 strains of bacteria for four weeks. The participants also underwent a colonoscopy and an upper endoscopy before they took the probiotic or placebo, and again after a four-week treatment period. (The upper endoscopy looked at the upper part of the digestive tract.) During these procedures, the researchers took samples from the participants’ intestines.

The researchers found that the probiotics were able to colonize the intestines of six of the participants. However, the rest were “resisters,” meaning that the bacteria did not colonize their gut, even though the probiotics were shed in their feces.

“While all of our probiotic-consuming volunteers showed probiotics in their feces, only some showed probiotics in their gut, which is where they needed to be,” co-principal author Eran Segal, a computational biologist at the Weizmann Institute, said in a statement.” If some people resist them and only some people allow them, then the benefits of the standard probiotics we all take are unlikely to be as widespread as we once thought.”

After further analysis of the data, the researchers found that they could predict whether probiotics would take root in people’s gut by examining the microbiome and gene expression in the gut photographed at the start of the study. However, this prediction method needs to be confirmed in future studies. The researchers call for further research to better understand why some people resist probiotic colonization, as future studies may enable researchers to counteract this resistance.

Harmful effects?

In a separate study involving 21 healthy volunteers, also published today in the journal Cell, the same group of researchers found that taking probiotics after treatment with broad-spectrum antibiotics may actually delay the recovery of people’s normal gut microbiome. This runs counter to the idea that probiotics can help people “repopulate” after antibiotics wipe out their gut bacteria.

“Contrary to the current dogma that probiotics are harmless and benefit everyone, these results reveal a new potential adverse side effect of using probiotics with antibiotics,” Elinav said.

The findings also underscore the need for personalized probiotic therapy to protect people’s gut health “without compromising microbiome recolonization,” the researchers said.

Dr. Arun Swaminath, director of the inflammatory bowel disease program at Lenox Hill Hospital, who was not involved in the study, said the findings “raise questions about whether probiotics really delay … the return of [healthy] bacterial ecosystems after” a person takes certain antibiotics.

However, whether these findings hold true in patients with specific medical conditions and exposure to different antibiotics “remains to be seen,” Swaminath told Live Science. “But it clearly suggests that probiotics may have an undeserved status in the current popular culture where they are considered naturally and indisputably healthy.”

The researchers also noted that they did not study clinical outcomes, such as whether probiotics helped relieve people’s gastrointestinal symptoms.