As science has learned more about the importance of healthy gut bacteria, the popularity of probiotic supplements has exploded. And so have new categories of supplements and substances aimed to help support your healthy microbiome. Read on to understand the definitions of and differences between probiotics, prebiotics, synbiotics, postbiotics, and parabiotics—and what they mean for your health.
What Are Probiotics?
The official definition of probiotics from The International Scientific Association for Probiotics and Prebiotics is: “Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.“1
In layman’s terms, probiotics are “good” bacteria strains, such as Lactobacillus acidophilus and Bifidobacterium bifidum, that you can take in supplement form, as in a pill, powder or liquid.
Of the terms discussed in this article, “probiotics” is the one that you are likely most familiar with. See further below for more information on probiotics including top probiotic foods, benefits of a healthy microbiome, and information on probiotic supplements, including their downsides.
What Are Prebiotics?
The official definition of prebiotics from The International Scientific Association for Probiotics and Prebiotics is: “A substrate that is selectively utilized by host microorganisms conferring a health benefit.”12
In this context, “substrate” means source of food. In other words, prebiotics are the source of food for your healthy gut bacteria.
Probiotic foods usually contain soluble fiber or resistant starch and include foods like apples, asparagus, and oats. A comprehensive list of probiotic foods is further below in this article.
What Are Synbiotics?
Synbiotics are simply supplements that contain a combination of probiotics and prebiotics.
You can purchase synbiotics, but will get the same benefit from eating probiotic and prebiotic foods together.
What Are Postbiotics?
The definition of postbiotics, according to a leading scientific paper, is: “Any substance released by or produced through the metabolic activity of the microorganism, which exerts a beneficial effect on the host, directly or indirectly.“13
In other words, postbiotics are the byproducts of probiotics. In supplement form, they are an attempt to capture the benefits or outputs of probiotics without needing the probiotics themselves. Postbiotics can include enzymes, amino acids, short-chain fatty acids, vitamins, and other substances. The benefits of postbiotics in supplement form may include the ability to supply these substances in a more pure form, in a controlled manner, and triggering only the desired response.15
This is new science, and there is no consensus about the value of postbiotics. My recommendation remains to favor eating probiotic (fermented) and prebiotic (high fiber/high resistant starch) foods over taking supplements, unless otherwise directed by your doctor.
What Are Parabiotics?
Parabiotics are “inactivated” probiotics. They may consist of fragments of microbes. The idea is that they would trigger the same benefits to your body as prebiotics, but without some of the potential side effects (see below), and in a controlled manner.
Parabiotics are so new that there is little research behind them, and they are not widely available for purchase. They may represent an important area of future study, however.
Now that we have defined these terms, let’s go back to Probiotics and Prebiotics and learn more about them:
Probiotics are intended to help improve the composition of your microbiome, which consists of trillions of microbes, including:
- Fungi, including yeast
It has been said that there are 10 times more microbes in your body than your own cells. More recent estimates say that the number of microbes is about the same as the number of cells in your body. In any event, we all have a lot of microbes3. Fun fact: they make up approximately 55% of your stool4. The majority of them reside in your gastrointestinal system, but they can be found throughout your body and on your skin, from head to toe.
It is estimated that there are over 2,000 species of microbes in your gut. A greater diversity of species is associated with better health5,6.
Everyone’s microbiome is unique—it’s like a fingerprint. Even twins have different microbiomes. Your microbiome changes constantly based on what you eat, infections, medications and other factors3.
By the way, my favorite book on the microbiome is called “I Contain Multitudes,” by Ed Yong. It’s fascinating, easy to understand and will make you think differently about what it means to be human.
It’s generally better to get your probiotics from food than from supplements if you can8. Experts say that nutrients like probiotics may interact with other substances in the food in ways* that help them provide their health benefits better than when isolated and concentrated.
Probiotics occur naturally in fermented foods including:
- Sauerkraut (not the shelf-stable kind)
- Sourdough bread
- Certain cheeses (cottage, swiss, provolone, gouda, cheddar, edam, gruyère)
- Pickles (not made with vinegar)
Sourdough bread is not on the list because the live cultures are destroyed during baking.
* Such as through the “buffering properties of foods for probiotics during passage through the gut, provision of essential nutrients for maintaining the activity and efficacy of the probiotic bacteria, synergistic effects of food ingredients on probiotic growth and consumer attitude towards probiotic foods vs. supplementation with tablets, capsules and other drug forms.”8
Benefits of a Healthy Microbiome
Your microbiome confers its benefits in a variety of ways, according to the Cleveland Clinic2, including decreasing colonization of harmful bacteria. In addition, your good microbes can, among other things:
- Help your body digest food
- Regulate your immune system
- Synthesize and manufacture vitamins and hormones
- Support your gut lining and prevent “leaky gut”
- Process medications
Benefits of these actions may include7:
- Weight loss
- Improved digestion
- Healthier skin (improved rosacea, acne)
- Improved mental health (anxiety, depression, OCD and potentially autism)13,14
- Reduced risk of numerous other diseases including obesity, diabetes, IBS, Crohn’s Disease, atherosclerosis
There are literally thousands of probiotic supplements to choose from—3,000+ on amazon.com.
They consist of any combination of dozens of different, beneficial bacterial strains that are thought to have different effects on your health. Each dose may contain billions of live bacteria, because large numbers are needed to ensure that some are able to colonize the hostile environment of the gut.
There is no clear consensus on which probiotic supplement to choose. It’s always better to get your nutrition from food, but talk to your doctor if you want to try a supplement. The best one for you will be based on what health issue you are trying to address.
Probiotic Supplement Downsides
People with a compromised immune system should not take probiotics other than under the supervision of their physician.
Some studies have shown, contrary to expectations, that supplementing probiotics actually delayed recovery of the gut microbiome9,10.
Probiotics can have side effects like gas and bloating11.
Probiotic foods include:
- Dandelion greens
- Whole grains including whole wheat
As an aside, the value of whole grains, beans, and legumes to your microbiome is one reason that I am not a fan of low-carb diets.
Some foods are fortified with probiotics by the manufacturer. They will appear on the label as:
- Galactooligosaccharides (GOS)
- Fructooligosaccharides (FOS)
- Chicory fiber
Summing it Up
In a nutshell:
- Prebiotics are healthy bacteria
- Probiotics are the food your healthy bacteria “eat”
- Synbiotics are a combination of prebiotics and probiotics
- Postbiotics are byproducts or “output” of probiotics
- Parabiotics are deactivated probiotic microbes
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1 Hill, C., Guarner, F., Reid, G., Gibson, G. R., Merenstein, D. J., Pot, B., Morelli, L., Canani, R. B., Flint, H. J., Salminen, S., Calder, P. C., & Sanders, M. E. (2014). Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nature reviews. Gastroenterology & hepatology, 11(8), 506–514. https://doi.org/10.1038/nrgastro.2014.66.
3 Allaband, C., McDonald, D., Vázquez-Baeza, Y., Minich, J. J., Tripathi, A., Brenner, D. A., Loomba, R., Smarr, L., Sandborn, W. J., Schnabl, B., Dorrestein, P., Zarrinpar, A., & Knight, R. (2019). Microbiome 101: Studying, Analyzing, and Interpreting Gut Microbiome Data for Clinicians. Clinical gastroenterology and hepatology : the official clinical practice journal of the American Gastroenterological Association, 17(2), 218–230. https://doi.org/10.1016/j.cgh.2018.09.017.
4. Stephen, A. M., & Cummings, J. H. (1980). The microbial contribution to human faecal mass. Journal of medical microbiology, 13(1), 45–56. https://doi.org/10.1099/00222615-13-1-45.
5. Thursby, E., & Juge, N. (2017). Introduction to the human gut microbiota. The Biochemical journal, 474(11), 1823–1836. https://doi.org/10.1042/BCJ20160510.
6. Deng, F., Li, Y., & Zhao, J. (2019). The gut microbiome of healthy long-living people. Aging, 11(2), 289–290. https://doi.org/10.18632/aging.101771.
7 Hills RD, Pontefract BA, Mishcon HR, Black CA, Sutton SC, Theberge CR. Gut Microbiome: Profound Implications for Diet and Disease. Nutrients. 2019; 11(7):1613. https://doi.org/10.3390/nu11071613.
8 Homayoni Rad, A., Vaghef Mehrabany, E., Alipoor, B., & Vaghef Mehrabany, L. (2016). The Comparison of Food and Supplement as Probiotic Delivery Vehicles. Critical reviews in food science and nutrition, 56(6), 896–909. https://doi.org/10.1080/10408398.2012.733894.
9 Suez, J., Zmora, N., Zilberman-Schapira, G., Mor, U., Dori-Bachash, M., Bashiardes, S., Zur, M., Regev-Lehavi, D., Ben-Zeev Brik, R., Federici, S., Horn, M., Cohen, Y., Moor, A. E., Zeevi, D., Korem, T., Kotler, E., Harmelin, A., Itzkovitz, S., Maharshak, N., Shibolet, O., … Elinav, E. (2018). Post-Antibiotic Gut Mucosal Microbiome Reconstitution Is Impaired by Probiotics and Improved by Autologous FMT. Cell, 174(6), 1406–1423.e16. https://doi.org/10.1016/j.cell.2018.08.047.
10 Suez et al., 2018, Cell 174, 1406–1423. September 6, 2018 ª 2018 Elsevier Inc. https://doi.org/10.1016/j.cell.2018.08.047.
12 Gibson, G., Hutkins, R., Sanders, M. et al. Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nat Rev Gastroenterol Hepatol 14, 491–502 (2017). https://doi.org/10.1038/nrgastro.2017.75.
13. Wang, H., Lee, I. S., Braun, C., & Enck, P. (2016). Effect of Probiotics on Central Nervous System Functions in Animals and Humans: A Systematic Review. Journal of neurogastroenterology and motility, 22(4), 589–605. https://doi.org/10.5056/jnm16018.
14. Akkasheh, G., Kashani-Poor, Z., Tajabadi-Ebrahimi, M., Jafari, P., Akbari, H., Taghizadeh, M., Memarzadeh, M. R., Asemi, Z., & Esmaillzadeh, A. (2016). Clinical and metabolic response to probiotic administration in patients with major depressive disorder: A randomized, double-blind, placebo-controlled trial. Nutrition (Burbank, Los Angeles County, Calif.), 32(3), 315–320. https://doi.org/10.1016/j.nut.2015.09.003.
15. Nataraj, B.H., Ali, S.A., Behare, P.V. et al. Postbiotics-parabiotics: the new horizons in microbial biotherapy and functional foods. Microb Cell Fact 19, 168 (2020). https://doi.org/10.1186/s12934-020-01426-w.