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What Are Prebiotics And How Do They Work?

And how do #prebiotics differ from #probiotics? Experts weigh in on how these trendy supplements may influence your well-being.

#microbiota #microbiome #bacteria #prebiotic #probiotic

Browse the aisles of any health food store or drugstore, and you’re likely to find prebiotic supplements. They’re packaged as powders, gummies, pills and drinks and claim to improve digestion, boost the immune system, lower blood sugar and more.

According to Grand View Research, a market research firm, the prebiotics market is projected to grow about 15 percent each year from 2022 to 2030 — in part because of rising concerns among consumers about gut issues like constipation, irritable bowel syndrome, acid reflux and inflammatory bowel disease.

But what exactly are prebiotics? And do you need to take them for good health?

What are prebiotics?

People frequently confuse prebiotics with probiotics — the live microorganisms found in foods like kimchi and some yogurts as well as in supplements that are intended to benefit health.

But prebiotics are substances that promote the growth of beneficial microbes in the gut. They can be found in fiber-rich foods like green bananas, asparagus, artichokes, garlic, onion, barley and wheat bran. Justin L. Sonnenburg, a professor of microbiology and immunology at Stanford University, said that prebiotic supplements typically contain purified types of dietary fiber that humans can’t digest.

The main purpose of prebiotics is to feed the diverse mix of beneficial bacteria that the gut needs to thrive, Dr. Sonnenburg said. A flourishing microbiome has been associated with various health benefits, including reduced risks of certain conditions like diabetes and obesity.

Gail Cresci, a microbiome researcher in pediatric gastroenterology at Cleveland Clinic Children’s Hospital, said that prebiotic and probiotic supplements are sometimes packaged together into one supplement. And some types of fiber supplements are also considered prebiotics, Dr. Sonnenburg said.

Do prebiotics help your gut?

A number of small studies have found that prebiotics — in supplemental and food form — are associated with regulating gut inflammation, alleviating constipation and supporting overall digestive health. But there’s less research on prebiotics than there is on probiotics in general, and their findings have been mixed and limited. More research is needed, Dr. Sonnenburg said.

In one 2018 trial of 44 people with certain gastrointestinal disorders that caused flatulence, for instance, researchers investigated how taking a prebiotic supplement helped to reduce symptoms in comparison with following a low-FODMAP diet. After four weeks, both methods were equally effective.

In another 2018 study, researchers reviewed several dozen studies on the effectiveness of prebiotics, probiotics, synbiotics (a mixture of probiotics and prebiotics) and antibiotics in managing irritable bowel syndrome. They found few studies showing that prebiotics, alone or in combination with probiotics, could benefit patients with the condition. A subsequent 2020 review of 33 randomized control trials reached similar conclusions.

There is some evidence to suggest that prebiotic supplements may help with constipation by encouraging more regular, frequent and well-formed bowel movements, Dr. Cresci said.

Indeed, if you are constipated, prebiotics could induce a laxative effect, said Kelly Swanson, a professor of animal and nutritional sciences at the University of Illinois at Urbana-Champaign.

There’s also preliminary research suggesting that prebiotics might help strengthen the immune system, Dr. Swanson added, but that evidence is inconclusive. He said, however, that he had researched how specific prebiotics might affect the abundance and activity of microbes in the intestinal microbiome and that prebiotics “clearly modify” the bacteria in our gut in beneficial ways.

Dr. Reezwana Chowdhury, an assistant professor of medicine at Johns Hopkins Medicine, said that she’s not aware of any data showing significant dangers associated with taking prebiotic supplements. But there also isn’t enough evidence showing that prebiotics are beneficial when treating conditions like irritable bowel syndrome or diarrhea, she said, so she has never recommended prebiotic supplements to her patients.

Dr. Lisa Ganjhu, an associate professor at the N.Y.U. Grossman School of Medicine who specializes in gastroenterology, agreed. The average person does not need to take prebiotics, she said. Some people who take them may notice some benefits, she added, but some may even notice worsened symptoms, including changes to bowel movements, more gas and more bloating.

If you do decide to try them, these supplements are generally safe and typically have few side effects, Dr. Swanson said. He noted that some people might experience more flatulence and loose stools after taking them, especially if the prebiotics are taken in higher-than-recommended amounts. To minimize that risk, Dr. Swanson suggested taking no more than five grams per day.

And don’t expect the supplement to transform your gut radically, Dr. Cresci said. “The prebiotic is not going to save the day from a bad diet,” she said. “There’s no magic bullet for that.”

What can you do instead of taking a prebiotic?

When it comes to nourishing the good bacteria in your gut, Dr. Sonnenburg said, following a fiber-rich diet with plenty of fruits and vegetables will likely be better for you.

We each have hundreds of species of bacteria blossoming in our intestines, and “it’s very difficult to imagine how putting one purified prebiotic into this community could foster the kind of biodiversity you need in your gut microbiome,” he said.

This doesn’t mean you have to eat a pound of asparagus every day for good health, Dr. Swanson said. But making a point to eat bananas throughout the week, he said, or swapping sugary breakfast pastries for healthier choices like oatmeal topped with nuts and berries, will help the good bacteria in your gut thrive.

Adding more fiber into your diet, which evidence suggests the average person in the United States could benefit from doing, will give you many of the same benefits of prebiotics, Dr. Sonnenburg said, since fiber stimulates the growth of beneficial bacteria in your intestine. The American Heart Association recommends that most people get at least 25 to 30 grams of dietary fiber per day.

To meet that goal, experts from the University of California, San Francisco, recommend aiming for at least five servings of fruits and vegetables each day and including at least one serving of whole grains in every meal. You can boost your fiber intake by adding lentils and legumes to soups and salads or whipping chia seeds into smoothies. You can also make some intentional swaps in your diet: Substitute brown rice for white rice and, when buying cereal, choose a product with at least five grams of fiber per serving. These alterations could have a more transformative effect on your gut than reaching for a prebiotic.

“Very few things are solved just by popping a pill,” Dr. Swanson said.

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