A Complete Guide to Prebiotics and What They Do

Medically Reviewed
onions soybeans asparagus leeks garlic bananas prebiotics
These common foods contain the fuel your microbiome needs to stay healthy.Canva; iStock
The food you eat is nourishing more than just you. Fruits, vegetables, whole grains, and beans are also feeding the bacteria living in your gut. You’re probably familiar with these “good” bacteria, which are known as probiotics — and collectively as the gut microbiome. But the fuel for those bacteria are specific nutrients called prebiotics, and there’s growing evidence that consuming those nutrients regularly may be key to keeping your beneficial bacteria thriving, and keeping you healthy overall. This guide will explain everything you need to know about prebiotics and how they impact your health.

What Are Prebiotics?

To understand prebiotics, we need to understand the microbiome, the community of microorganisms, including bacteria, fungi, and viruses living on and in the human body. This collection of microorganisms is located primarily in the gut, and they work together to protect you from infections and other health risks.

The good bacteria in your gut are called probiotics. They occur there naturally, but you can increase their numbers by eating fermented foods or taking probiotic supplements. These bacteria eat the food you eat: Nutrients that humans can’t digest are consumed by the bacteria, helping them to thrive. Those nutrients are called prebiotics.

Katie Guzzetta, PhD, visiting?researcher in the neurology department at Brigham and Women’s Hospital and Harvard Medical School in Boston, gives this brief rundown of the biotics family:
  • Prebiotics: nutrients we consume that support the health of our gut microbes
  • Probiotics: bacteria that provide a known health benefit to the host
  • Synbiotics: a combination of pre- and probiotics that work together to provide a health benefit to their host
  • Postbiotics: bioactive compounds produced by bacteria that provide a health benefit — the products of probiotics consuming prebiotics

Common Questions & Answers

What do prebiotics do for you?
Prebiotics support the good bacteria in your gut. They can lower your risk for heart disease, reduce and shorten bouts of diarrhea, reduce inflammation and protect against colon cancer.
What are some prebiotic foods?
Any fruits, vegetables, whole grains, and beans can be a good source of prebiotics. Onions, garlic, leeks, bananas, asparagus, artichokes, and soybeans are especially high in prebiotics.
Is it better to take prebiotics or probiotics?
You need both, ideally from a variety of whole foods, not supplements. Prebiotics are fuel for probiotics, and are necessary to optimally support gut health, which impacts many other aspects of health.
What are the dangers of prebiotics?
Prebiotics carry very little risk. If you’re ingesting them regularly for the first time, you may feel gassy or feel your stomach gurgling. If you take a lot of them, you might feel stomach pain or have diarrhea. Researchers suggest that if you have irritable bowel syndrome or gastroesophageal reflux (GERD), your risk for side effects might be higher.
Do I need a prebiotic supplement?
No. Most experts recommend getting prebiotics naturally from the food you eat, focusing on complex carbohydrates. If you do take a supplement, know that only the safety of probiotics in food is regulated by the US. Food and Drug Administration (FDA), not their effectiveness.

What Are the Potential Benefits of Prebiotics?

Prebiotics have some great benefits for human health. People who eat lots of fruits and vegetables have lower instances of colorectal cancers. Certain prebiotics have been shown to prevent gut inflammation and infection from some types of salmonella — a kind of bacteria that causes food poisoning.

Prebiotics have been shown to help improve the microbiome and improve immunity in infants.

There’s promise for adult immunity, too, but more research is needed to prove prebiotics’ immune benefits.

What Foods Contain Prebiotics?

Think about high-fiber foods, “what grandma used to call roughage,” says Debbie Petitpain, RDN, a spokesperson for the Academy of Nutrition and Dietetics based in Charleston, South Carolina. Fruits, vegetables, whole grains, and beans will provide the insoluble fiber gut bacteria thrive on. “It’s funny that we did this phase of ‘I don’t eat anything white,’ because white vegetables — onions, garlic, leeks — those are rich in prebiotics,” she added. Bananas, asparagus, artichokes, soybeans, chickpeas, oats, and berries all have prebiotic benefits, too.

Some foods are marketed as having prebiotics added to them. Their safety is regulated by the FDA, but not their effectiveness.

The FDA does not have an established definition for prebiotics, either — it allows food and supplement manufacturers to self-report their products as “generally recognized as safe,” or GRAS.

The 411 on Probiotic Supplements and How to Choose a Quality Product

Prebiotic supplements are also available over the counter in drug stores and supermarkets across the United States. You might be tempted to try one out, especially if you’re feeling constipated. Just be aware that manufacturers can put a product on the market without FDA approval, and only if safety concerns arise will the FDA intervene. And the efficacy of supplements — whether they do what they claim — is not regulated at all. That said, there are some steps you can take to make sure you’re getting a quality product. Karen Hecht, PhD, scientific affairs manager at AstaReal in Burlington, New Jersey, suggests looking at a few things:

  • “If your product has a branded ingredient … you have something to follow up on,” Dr. Hecht said. If a supplement has a branded ingredient, with a trademark or registered trademark symbol on the label, you can look at the product’s website to see what types of independent testing have been done to prove that ingredient’s efficacy. You can also search the National Institutes of Health PubMed to see what studies have been done publicly about the product’s efficacy, including dose size.
  • Look for products that have a Good Manufacturing Practices (GMP) or United States Pharmacopeial Convention (USP) certification seal on the label. The FDA issues guidance on current good manufacturing practices.

  • While the United States does not regulate supplements’ efficacy, Canada and Europe do. You can look up a product or an ingredient on Health Canada’s Licensed Natural Health Products Database to see if it has been shown to do what the product claims.

    “Health Canada does review and approve health claims,” Hecht said. “They don’t let supplements put a health claim on the bottle unless the science has been reviewed and approved by Health Canada first, and they approve the wording.” Note that you can only look up brands or ingredients, not the word “prebiotic.”

One possible drawback to supplements is that they can be expensive. “If you’re specifically looking to rebalance the bacteria in your gut, you get more bang for your buck through whole foods,” Petitpain says. “Consumers should aim to consume the recommended number of fruits, veggies, and whole grains before adding supplements.”

Do Prebiotics Have Any Potential Health Risks?

Prebiotics are generally very safe. If you’re getting your prebiotics through food, and you’re already pretty healthy, there’s no real consensus on what might be “too much.” Some studies, however, have shown that very sick people, including those with organ failure, may have gotten even sicker or even died when given probiotics and prebiotics through a feeding tube placed in the small intestine.

Talk to your doctor before taking any supplements or increasing your prebiotic intake. They may recommend that you stagger fiber or prebiotic supplements with your medication, so your medication can be fully absorbed.

Summary

Prebiotics are an important part of keeping your microbiome healthy, supporting your immune system. The best way to get them is to eat lots of healthy foods.

Editorial Sources and Fact-Checking

Show Less