Is Your Gut Missing Out? The Basics of Prebiotics, Probiotics, Synbiotics, and Postbiotics

You don’t have to look far to see the recent increase in attention that prebiotic and probiotics are getting. Thousands of supplements, drinks, and foods with prebiotics and probiotics have shown up on the market. Do you need to take a prebiotic and probiotic? Do supplements work? As a Registered Dietitian Nutritionist, I am able to work with my clients to help them decide if a prebiotic and probiotic is the right choice.

Gut 101

To understand prebiotics and probiotics, we need to understand our guts. Your gastrointestinal tract is the part of your digestive system that digests food, absorbs nutrients, and secretes waste products. Your gastrointestinal tract has trillions of microbes. We host these microbes and provide them a place to live, and in exchange, many provide us with health benefits. Our gut microbiota helps you digest food, aid in immune function, and helps fight off bad bacteria.

Your gut microbiota is like a snowflake: there are other ones out there, but none are quite like yours! Each individual has a different gut microbiota, which makes it difficult to determine what a “healthy” gut microbiota looks like. While there is no ideal gut microbiota, greater microbial diversity appears to play a role in our overall health.

Your diet plays the biggest role in achieving gut microbiota diversity. The standard Western diet has been shown to decrease microbial diversity. The good news? Consuming a variety of foods, especially fiber-rich, plant-based foods, can encourage gut microbiota diversity.

If you have ever taken an antibiotic (which is anti-bacteria and wipes out most of the bacteria, good and bad, in your gut microbiota ), you have experienced firsthand how quickly our gut microbiota can be altered. After your course of antibiotics, the good bacteria will be reintroduced by the foods you eat, and your gut balance will likely restore.

Key Takeaway: Our gut microbiota helps us digest food, aid in immune function, and fight off bad bacteria.

Prebiotics and Probiotics: What’s the Difference?

Probiotics are outside sources of live microorganisms that have been shown to provide us with health benefits. When we think of probiotics we typically think of bacteria, but some probiotics also contain yeast. Prebiotics are the food that our residential microbes eat and in turn, provide us with health benefits. Most prebiotics are a type of fiber that we are unable to digest and instead travel down to our gut microbiota where the magic happens!

What Is a Prebiotic?
To put it simply, a prebiotic is the “food” that your gut microbes eat. You cannot digest the type of fiber in a prebiotic, but your gut bacteria can. Vegetables, fruits, whole grains, and legumes like beans and lentils are the best sources of naturally occurring prebiotic fiber. According to the International Scientific Association for Prebiotics and Probiotics (ISAPP), prebiotics are also added to some food items such as yogurts, cereals, breads, biscuits, desserts, or drinks. You likely won’t see the word ‘prebiotic’ on the label, you can find them in the ingredient list. Look for galacto-oligosaccharides (GOS), fructo-oligosaccharides (FOS), oligofructose (OF), chicory fiber, or inulin.

When it comes to prebiotics, the best thing you can do to support good gut health is to try to get it from the foods you eat. There are a few instances when taking a prebiotic supplement may be warranted but in most cases, we can get all the prebiotics we need by eating a variety of plant-based foods. You’ll want to work with a Registered Dietitian Nutritionist to see if taking a prebiotic supplement would be right for you.

Fiber and Prebiotics
In general, most people don’t get enough fiber. The average person consumes about 16 grams of fiber, which is less than the daily recommended amount for adults. Fiber is important because it regulates our bowel movements, helps us feel fuller longer, and provides necessary prebiotics for your gut microbes to feast on.

When it comes to prebiotic fiber, things get specific: Most prebiotics are fibers, but not all fibers are prebiotics. The ISAPP recommends consuming at least 5 grams of prebiotics daily for improved gut health. Working with a Registered Dietitian Nutritionist can help ensure that you are eating the right types of fiber needed to support good gut health.

How Does a Prebiotic Work?
Let’s say you eat something that is prebiotic. This undigested fiber makes its way to the large intestine, where it is fermented by gut bacteria. During the fermentation process, something called short-chain fatty acids are produced. While the diet world has made us afraid of anything with the word “fat” in it, short-chain fatty acids are an incredibly beneficial thing. Your body needs short-chain fatty acids to thrive!

Key Takeaway: Prebiotics provide the energy for the good bacteria to do their job. The recommended amount of prebiotic fiber is 5 grams a day, and you should focus on getting your prebiotic fiber from the food that you eat.

What Are Probiotics?
Probiotics are living microorganisms that are similar to the ones you can find in your gut, but they are available in outside sources. For a supplement or food to be considered a “probiotic”, it must contain live microorganisms that provide health benefits when given in sufficient amounts.

Fermented foods like yogurt, kimchi, and sauerkraut can contain live bacteria if they haven’t been killed off during food processing . But, not all fermented foods with live bacteria meet the definition of a probiotic.

What Are The Benefits of Probiotics?
According to the ISAPP, probiotics have been proven to help your body in a variety of ways. Probiotics may:

  • Assist with your immune function
  • Aid your digestion
  • Keep harmful microorganisms in check
  • Aid in nutrient absorption

Additionally, certain probiotics can reduce antibiotic-associated diarrhea, improve mild to moderate irritable bowel syndrome, help manage symptoms associated with poor digestion of lactose, reduce colic symptoms and reduce risk of eczema in infants, and even decrease the risk of some common infections, including those of the respiratory tract, gut, and vaginal tract.

Probiotics are generally considered safe, but if you have an immune condition, a severe illness or before giving to an infant you should consult with your doctor.

Key Takeaway: Probiotics are beneficial bacteria that can help us digest food, absorb nutrients, and fight off bad bacteria. Probiotics have different strains and need to be taken in different amounts. A Registered Dietitian Nutritionist can help you determine if there is a probiotic out there that may be right for you.

Synbiotics and Postbiotics

Synbiotics is a supplement that contains a combination of both prebiotics and probiotics. The idea is that the combination of the two will work in synergy to provide us with enhanced health benefits. While the idea sounds great, the research is still limited.

In addition to synbiotics, you might have heard of postbiotics. Postbiotics are a byproduct of the fermentation process that takes place when your gut microbes feast on prebiotics. Postbiotics are currently being observed in clinical settings because of their possible health benefits. They, like synbiotics, are becoming readily available in supplement form.

Key Takeaway: Don’t go running to the store just yet, more evidence is needed on these two supplements before you should start investing in them.

How Can I Get Great Gut Health?

Research on the microbiome is still relatively new. New research and findings are coming out all of the time. The information out there can sometimes feel confusing, or overwhelming. Additionally, your needs are very specific! The foods you eat, the medications you take, and lifestyle factors can all affect your gut health.

In general, focus on consuming a variety of plant-based foods to feed and diversify your gut microbiota. By working with a Registered Dietitian Nutritionist, you can get a personalized plan to meet your gut health needs.

1. “All About Antibiotics.” Gastrointestinal Society, 30 June 2021,
2. Davani-Davari D, Negahdaripour M, Karimzadeh I, Seifan M, Mohkam M, Masoumi SJ, Berenjian A, Ghasemi Y. Prebiotics: Definition, Types, Sources, Mechanisms, and Clinical Applications. Foods. 2019; 8(3):92.
3. Holzapfel, Wilhelm H., and Ulrich Schillinger. “Introduction to Pre- and Probiotics.” Food Research International, vol. 35, no. 2-3, Elsevier, 2002, pp. 109–16, doi:10.1016/S0963-9969(01)00171-5.
4. Hornbuckle, William E. et al. “Gastrointestinal Function.” Clinical Biochemistry of Domestic Animals (2008): 413–457. doi:10.1016/B978-0-12-370491-7.00014-3
5. Julio Plaza-Diaz, Francisco Javier Ruiz-Ojeda, Mercedes Gil-Campos, Angel Gil, Mechanisms of Action of Probiotics, Advances in Nutrition, Volume 10, Issue suppl_1, January 2019, Pages S49–S66,
6. Justin L Carlson, Jennifer M Erickson, Beate B Lloyd, Joanne L Slavin, Health Effects and Sources of Prebiotic Dietary Fiber, Current Developments in Nutrition, Volume 2, Issue 3, March 2018, nzy005,
7. Linares, Daniel M et al. “Beneficial Microbes: The pharmacy in the gut.” Bioengineered vol. 7,1 (2016): 11-20. doi:10.1080/21655979.2015.1126015
8. Onyszkiewicz, Maksymilian, Kinga Jaworska, and Marcin Ufnal. “Short chain fatty acids and methylamines produced by gut microbiota as mediators and markers in the circulatory system.” Experimental Biology and Medicine 245.2 (2020): 166-175.
9. Patel, Ravi Mangal, and Patricia Wei Denning. “Therapeutic use of prebiotics, probiotics, and postbiotics to prevent necrotizing enterocolitis: what is the current evidence?.” Clinics in perinatology vol. 40,1 (2013): 11-25. doi:10.1016/j.clp.2012.12.002
10. Salminen, S., Collado, M.C., Endo, A. et al. The International Scientific Association of Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of postbiotics. Nat Rev Gastroenterol Hepatol 18, 649–667 (2021).
11. Silva, Ygor Parladore, Andressa Bernardi, and Rudimar Luiz Frozza. “The role of short-chain fatty acids from gut microbiota in gut-brain communication.” Frontiers in endocrinology 11 (2020): 25.
12. Swanson, Kelly S et al. “The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of synbiotics.” Nature reviews. Gastroenterology & hepatology vol. 17,11 (2020): 687-701. doi:10.1038/s41575-020-0344-2
13. Tomova, Aleksandra et al. “The Effects of Vegetarian and Vegan Diets on Gut Microbiota.” Frontiers in nutrition vol. 6 47. 17 Apr. 2019, doi:10.3389/fnut.2019.00047
14. UCSF Health. “Increasing Fiber Intake.”, University of California San Francisco Health, 22 June 2021,
15. Valdes A M, Walter J, Segal E, Spector T D. Role of the gut microbiota in nutrition and health BMJ 2018; 361 :k2179 doi:10.1136/bmj.k2179

Leave a comment!

Leave a Reply

Hi there! I'm Tiana

A Registered Dietitian Nutritionist specializing in nutrition counseling for digestive disorders and gut health.

Don't miss the freebie!