Taking powders and capsules of live microorganisms can disrupt the balance of bacteria in the intestinal tract of healthy people and lead to less microbial diversity, say scientists, who warn that in healthy people, probiotic supplements offer little benefit and can sometimes do more harm than good.
These 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 studies say beware of the hype, reports The Washington Post.
Probiotic supplements come in the form of capsules, gummies, powders and pills that contain live microorganisms believed to boost gut health.
Some people who may benefit from taking them include those with gastrointestinal ailments. Studies have found that probiotic supplements can reduce symptoms of irritable bowel syndrome and inflammatory bowel disease: they can also prevent traveller’s diarrhoea and reduce some side effects of antibiotics.
But for most people, more reliable ways are available to nourish your gut microbiome.
Eating vegetables, nuts, seeds, beans and whole grains will provide the gut microbes with the fibre-rich fuel they need, while fermented foods like yogurt, sauerkraut, kimchi and kefir, which contain probiotics and other beneficial compounds, have positive effects on gut microbiome.
Crowding out the wrong microbes
Gut microbes are part of a vast ecosystem of bacteria, viruses, archaea and fungi located largely in the colon. People who harbour diverse gut microbiomes tend to age more healthfully and develop fewer diseases.
These microbes thrive on the fibre found in fruits and vegetables, turning it into new compounds or “postbiotics”, including butyrate, acetate, and other short-chain fatty acids that are good for your health.
But sometimes the microbes can work together and compete against one another. Sometimes the proportion of good and bad bacteria in the gut can get out of balance – a condition known as dysbiosis.
Although there are numerous brands of probiotic supplements, many contain a limited number of bacterial strains, primarily from the groups lactobacillus, bifidobacterium and a few others. These micro-organisms 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 Programme at the University of Texas MD Anderson Cancer Centre.
“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.”
Probiotics on antibiotics
It’s common to take probiotics alongside antibiotic medications. While antibiotics treat bacterial infections, they can also wipe out beneficial bacteria, so a probiotic supplement with an antibiotic helps rebalance the gut microbiome and minimise side effects. Studies have shown, for example, that probiotics can prevent antibiotic-associated diarrhoea.
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 week-long 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.
Different effects in different people
In another recent clinical trial, scientists at Stanford University 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.”
To take or not to take?
Some doctors might advise skipping probiotics altogether if patients have a severe illness or compromised immune system, because of the risk of developing an infection.
Others 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 Cente at the University of Washington Medical Centre. “Fermented foods are like nature’s probiotics.”
Fermented foods typically contain not just probiotics (the live microbes) but also prebiotics (the fibre the microbes eat) and postbiotics (the vitamins and other nutrients they produce).
Study details
Randomized controlled trial demonstrates response to a probiotic intervention for metabolic syndrome that may correspond to diet
Hannah Wastyk, Dalia Perelman, Madeline Topf, Gabriela Fragiadakis, Jennifer Robinson et al.
Published in Gut Microbes on 19 February 2023
Abstract
An individual’s immune and metabolic status is coupled to their microbiome. Probiotics offer a promising, safe route to influence host health, possibly via the microbiome. Here, we report an 18-week, randomised prospective study that explores the effects of a probiotic vs. placebo supplement on 39 adults with elevated parameters of metabolic syndrome. We performed longitudinal sampling of stool and blood to profile the human microbiome and immune system. While we did not see changes in metabolic syndrome markers in response to the probiotic across the entire cohort, there were significant improvements in triglycerides and diastolic blood pressure in a subset of probiotic arm participants. Conversely, the non-responders had increased blood glucose and insulin levels over time. The responders had a distinct microbiome profile at the end of the intervention relative to the non-responders and placebo arm. Importantly, diet was a key differentiating factor between responders and non-responders. Our results show participant-specific effects of a probiotic supplement on improving parameters of metabolic syndrome and suggest that dietary factors may enhance stability and efficacy of the supplement.
See more from MedicalBrief archives:
Off-the-shelf probiotics ‘are almost useless’
Probiotics improve nausea and vomiting in pregnancy
A review article on the clinical use of probiotics