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What You Need to Know About Prebiotics and Probiotics

Updated: Mar 27

Probiotics and prebiotics are very popular dietary supplements. After vitamins and minerals, more American adults use probiotics or prebiotics than any other supplement (1). And there is good reason for this. Not only is gut health becoming recognized as the foundation for overall physical health, but recent studies point to the influence a healthy gut has on mental health as well.

Probiotics and prebiotics promote health in many ways. For example, a gut full of “friendly” microbes will absorb more nutrients, discourage unfriendly microbes, and even reduce inflammation—all of which are beneficial to gut health and overall wellbeing. Besides supplements, many foods contain probiotics and prebiotics.

What are Probiotics and Prebiotics?

Before we dive into the ways that probiotics, prebiotics (and other “biotics”) can impact our health, and how to get enough of them, here are some quick definitions:

  • Microbiome - In the large intestine of your gut are trillions of “friendly” microbes that naturally inhabit this area (2,3,4). Most of these microbes are bacteria, but there are also some health-promoting viruses and fungi. All of these tiny organisms living together are called the microbiome. Everyone starts with a unique microbiome at birth and this is influenced by many factors including what we eat and what supplements and medications we take (2,3).

  • Probiotics - Probiotics are “live microorganisms that are intended to have health benefits when consumed or applied to the body” (1). The word comes from the Greek words “pro” and “bios” meaning “for life” (4).

  • Prebiotics - Prebiotics are “nondigestible food components that selectively stimulate the growth or activity of desirable microorganisms” (1). They’re essentially food for the microbes in your gut and they’re used to help grow a diverse, thriving microbiome (3,5). 

  • Psychobiotics - Psychobiotics are “probiotics that confer mental health benefits” (6).

Health benefits of pro-, pre-, and psychobiotics

Maintaining a balance of gut microbes benefits health in so many ways. The list of positive health effects of a healthy gut microbiome seems to grow daily because of all of the research in this area. Some of the key benefits include helping to digest food and promote gut health, producing essential nutrients, influencing the immune system, improving moods and mental health, and even reducing the impact of inflammation and toxin-producing microbes (1,3,7). Two that we will focus on for this article are gut health and mental health.

Gut health

The microbiome helps maintain and improve gut health in many ways. It contributes to healthy bowel function and may help with conditions such as colitis (1,2). Some studies show that probiotics can help with diarrhea and constipation (1), especially if the cause is due to an imbalance in the gut microbiome (8). 

How does a healthy gut microbiome achieve a healthy gut? There are a myriad of ways. First of all, certain microbes produce health-promoting substances such as short-chain fatty acids and certain B vitamins (4). These nutrients are absorbed by the body and go on to nourish other areas of the body. Other substances produced by gut microbes help to lower the pH of that part of the gut and reinforce its barrier (9). The gut microbiome can also reduce inflammation, eliminate toxins, as well as boost the body’s ability to absorb essential minerals (4).

Mood, mental health, and psychobiotics

There is a growing area of research about nutritional psychiatry—the links between what we eat and how we feel mentally and emotionally (7). Many studies show the strength of this food-mood connection. For example, eating a high-quality, nutritious diet nourishes the brain, helps keep inflammation down, and helps us enjoy more stable moods (7). Plus, many chronic gut conditions are often accompanied by mood disorders such as depression and anxiety (6). As mentioned earlier, there is a subset of probiotics that have mental health benefits called “psychobiotics” (6).

A recent review of seven clinical trials published in the medical journal BMJ Nutrition Prevention & Health found that certain probiotic supplements, with and without prebiotics, were linked to “measurable reductions in depression” (10).

How does gut health influence the mind and emotions? Mainly through what is called the “gut-brain axis.” Several parts of this axis foster constant communication in both directions between your gut and brain (6). Parts of the gut-brain axis include:

  • Some neurotransmitters and neurohormones are produced in the gut. For example, it’s estimated that 90-95 percent of the serotonin in the body is produced in the gut (6,7). Serotonin is the neurotransmitter that helps to regulate sleep, appetite, and emotions, and reduce pain (7). 

  • The digestive system contains 100 million nerve cells and is a hub for the immune system (7). 

  • A healthy gut microbiome helps to regulate the stress response and inflammation throughout the body (6). 

  • Some rodent studies suggest that the gut microbiome can influence levels of brain-derived neurotrophic factor (BDNF) in the central nervous system, thus impacting behavior (6).

All of these gut-brain activities are influenced by the gut microbiome and pro—or psycho—biotics (6,7).

How to get enough probiotics and prebiotics

Pro- and prebiotics can be found in both foods and supplements. 

Probiotic foods

Many gut-healthy, fermented foods are produced with the help of bacteria. Some of these include yogurt, kefir, pickles, sauerkraut, miso, and kombucha (2). However, not all fermented foods still contain live active cultures of those bacteria by the time they get to the market or grocery store shelf (2,9). Your best bet is to choose fermented products from the refrigerated section (3) and check the product labels to ensure they contain “live active cultures” (2). Also, some food companies are now fortifying unfermented foods (cereals, juices) with probiotics (9); so again, check your labels.

Prebiotic (fiber-rich) foods

Many foods are rich in the insoluble fiber that health-promoting gut microbes need to thrive. These include whole grains (oatmeal, whole grain breads, and pastas), vegetables (asparagus, leeks, onions), starchy vegetables (sweet potatoes, corn), fruit (bananas), and legumes (beans, lentils, peas) (2,4). Enjoy a variety of these fiber-rich foods to naturally boost the health and biodiversity of your microbiome (3).

In addition to eating probiotic and prebiotic foods, it’s also a good idea to limit foods that can deplete your friendly gut microbes. This includes enjoying fewer processed foods that are high in sugars, artificial sweeteners, and saturated fats (2,3). 

Probiotic supplements

There are many strains of probiotic microbes available, each having unique effects. Some of the most common strains included in probiotic supplements include Lactobacillus, Bifidobacterium, Saccharomyces, Streptococcus, Enterococcus, Escherichia, and Bacillus (9). Many of these strains are similar to those found naturally in the microbiome (1). Supplement companies combine different strains of bacteria and yeasts in different amounts to create many unique supplements to choose from. 

Unlike with foods, the manufacture of probiotic supplements is not monitored in the US and some products have been found to have different or fewer probiotics than what’s listed on the label (8). This is why it’s important to choose a high-quality probiotic whenever possible. 

Note that probiotic supplements should not be given to premature infants or people with severe illnesses or compromised immune systems without a recommendation from a qualified healthcare professional, as there have been reports of harmful effects (1).

Prebiotic supplements

Prebiotic supplements contain starches that the gut microbes consume and metabolize into beneficial compounds. These fiber-rich supplements may include inulin, GOS (galactooligosaccharides), FOS (fructooligosaccharides), and lactulose (4).

Final thoughts

Gut health is more than just a well-functioning digestive system. Gut health influences physical and mental health in a myriad of ways. One of the main things that you can do to foster gut health is to nourish your gut’s microbiome. This includes enjoying probiotic (fermented) foods as well as prebiotic (fiber-rich) foods. Both probiotics and prebiotics are also available as dietary supplements when necessary.

Do you need help optimizing your gut health, overall health, or mental health? As a registered dietitian, I’d love to help. Book a Discovery Call with me today to see if my programs or services can help you!


  1. National Center for Complementary and Integrative Health. (2019, August). Probiotics: What You Need To Know.

  2. Harvard Health Publishing. (2022, November 14). Probiotics and prebiotics: what’s really important?

  3. Corliss, J. (2023, November 1). How a healthy gut helps your heart. Harvard Health Publishing.

  4. Ji, J., Jin, W., Liu, S. J., Jiao, Z., & Li, X. (2023). Probiotics, prebiotics, and postbiotics in health and disease. MedComm, 4(6), e420.

  5. Golen, T & Ricciotti, H. (2021, November 1). What are postbiotics? Harvard Health Publishing.

  6. Del Toro-Barbosa, M., Hurtado-Romero, A., Garcia-Amezquita, L. E., & García-Cayuela, T. (2020). Psychobiotics: Mechanisms of Action, Evaluation Methods and Effectiveness in Applications with Food Products. Nutrients, 12(12), 3896.

  7. Selhub, E. (2022, September 18). Nutritional psychiatry: Your brain on food. Harvard Health Blog.

  8. Harvard Health Publishing. (2022, February 2). Should you take probiotics?

  9. Office of Dietary Supplements. (2023, November 3). Probiotics: Fact Sheet for Health Professionals.

  10. British Medical Journal. (2020, July). Probiotics alone or combined with prebiotics may help ease depression.


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