What Are Prebiotics?

Health benefits, side effects, and what to look for

Table of Contents
View All
Table of Contents

Prebiotics are specialized plant fibers that stimulate the growth of healthy bacteria in the digestive tract. They mainly consist of fiber or complex carbohydrates that your body cannot digest. You can find prebiotics in foods like garlic and asparagus, as well as prebiotic supplements.

By stimulating the growth of bacteria like Lactobacillus and Bifidobacterium, prebiotics may help improve digestion, ease constipation, increase mineral absorption, regulate cholesterol, and strengthen the immune system.

Prebiotics differ from probiotics, which are foods or supplements that deliver healthy bacteria directly to your stomach and digestive tract.

This article offers an unbiased look at the potential health benefits of prebiotic foods and supplements, as well as the possible side effects and risks.

Health Benefits of Prebiotics

Prebiotics are components of plant-based foods that cannot be digested. Once eaten, they are degraded in the small intestine by healthy bacteria that grow and thrive on them. These are the "good" bacteria your body needs to digest food and control "bad" bacteria or yeast (like Candida that causes oral thrush).

The two main prebiotics important to human health are:

  • Fructo-oligosaccharides found in plants such as onion, chicory, garlic, asparagus, banana, and artichoke
  • Galacto-oligosaccharides found in beans and certain root vegetables

There is some evidence that prebiotics may improve digestion, increase calcium absorption, enhance immune function, prevent allergic conditions, lower cholesterol, improve brain function, and even reduce the risk of colon cancer.

Evidence and Debate

The role of prebiotics in general health is uncertain. Many of the health claims are weakly supported, and it is unclear whether your health can improve simply by increasing your intake of prebiotic-rich foods or supplements.

Prebiotics for Digestive Disorders

Some researchers suggest that prebiotics may play a role in the treatment of irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD). Study results to date have been mixed.

A 2013 study reported that a higher intake of prebiotics can actually make IBS symptoms worse. This is because many prebiotics are high in carbohydrates known as FODMAPs (fermentable, oligosaccharides, disaccharides, monosaccharides, and polyols). As these carbs break down and ferment, they can add to IBS symptoms such as gas, bloating, and abdominal pain.

On the other hand, IBD (Crohn’s disease and ulcerative colitis) is characterized by a lack of healthy gut bacteria. Some studies suggest that prebiotics, particularly fructan-oligosaccharides, can help ease gut inflammation and IBD symptoms.

Other studies have suggested that prebiotics may be safe and effective in preventing Clostridium difficile-associated diarrhea, which is commonly associated with antibiotic use or recent hospitalization.

Possible Prebiotic Side Effects

Most prebiotics can be safely consumed without side effects. If side effects do occur, they are generally mild and may include:

  • Bloating
  • Gas
  • Abdominal discomfort

These side effects usually ease as your digestive system adapts to the change in the intestinal environment.


Most people can get prebiotics by consuming the recommended daily intake of fiber (between 25 grams and 38 grams per day). Eating whole grains and plenty of fruits and vegetables is often the best way to reach this goal.

Many prebiotic supplements provide a dose of around four to five grams per day. If you take a prebiotic supplement, start slowly to see how your body reacts. If gas or bloating occurs, cut the dose in half.

What Is Synbiotic Therapy?

Synbiotic therapy is the combined use of prebiotics and probiotics. Because probiotics are short-lived, prebiotics can help maintain probiotic levels in the gut.

Prebiotic Foods

Foods are the best source of prebiotics as they provide good nutrition, including essential minerals, vitamins, and antioxidants.

Prebiotic foods include:

  • Asparagus
  • Chicory root
  • Fennel
  • Garlic
  • Jerusalem artichoke
  • Legumes (including beans, chickpeas, lentils, and soybeans)
  • Nuts (such as cashews and pistachios)
  • Onions, leeks, shallots, scallions
  • Wheat products (such as cereal and bread)

Prebiotic Supplements

If you are thinking about taking a prebiotic supplement, check the label to ensure it contains fructan-oligosaccharides and/or galacto-oligosaccharides.

Before starting treatment, speak with your healthcare provider to ensure that it is safe for you based on your medical conditions and any drugs your take.

To ensure purity and safety, opt for supplements certified by the U.S. Pharmacopeia (USP), ConsumerLab, or NSF International. Certification does not mean that the product is effective but indicates that it contains the ingredients on the product label without any contaminants.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Davani-Davari D, Negahdoripour M, Karimzadeh I. Prebiotics: definition, types, sources, mechanisms, and clinical applications. Foods. 2019 Mar;8(3):92. doi:10.3390/foods8030092

  2. Parker EA, Roy T, D'Adamo CR, Wieland LS. Probiotics and gastrointestinal conditions: an overview of evidence from the Cochrane Collaboration. Nutrition. 2018 Jan;45:125–34.e11. doi:10.1016/j.nut.2017.06.024

  3. Whelan K. Mechanisms and effectiveness of prebiotics in modifying the gastrointestinal microbiota for the management of digestive disorders. Proceed Nutrition Soc. 2013;72:288-98. doi:10.1017/S0029665113001262

  4. Rasmussen HE, Hamaker BR. Prebiotics and inflammatory bowel disease. Gastroenterol Clin North Am. 2017 Dec;46(4):783-95. doi:10.1016/j.gtc.2017.08.004

  5. Goldenberg JZ, Ma SS, Saxton JD, Martzen MR, Vandvik PO, Thorlund K, Guyatt GH, Johnston BC. Probiotics for the prevention of Clostridium difficile-associated diarrhea in adults and childrenCochrane Database System Rev. 2013;(5):CD006095. doi:10.1002/14651858.CD006095.pub3

  6. Office of Disease Prevention and Health Promotion. Dietary Guidelines for Americans, 2020-2025.

  7. Markowiak P, Śliżewska K. Effects of probiotics, prebiotics, and synbiotics on human health. Nutrients. 2017 Sep;9(9):1021. doi:10.3390/nu9091021

Additional Reading

By Barbara Bolen, PhD
Barbara Bolen, PhD, is a licensed clinical psychologist and health coach. She has written multiple books focused on living with irritable bowel syndrome.