Trillions of microorganisms—along with 100 times more genes than the entire human genome—compose our gut microbiota [1]. This complex ecosystem plays vital roles in digestion, immunity, vitamin production, and protection against infections. The evidence is clear: our gut microbiota is a major ally for our health.

While the precise microbial signature of a “healthy microbiota” remains uncertain, a diverse microbiota is generally associated with optimal health. Conversely, an imbalance in this microbial community can negatively impact our health [2].

In recent years, the term “Biotics” has gained popularity due to its role in modulating the gut microbiota. An increasing body of evidence supports the beneficial effects of biotics on digestive health and overall wellness. Everywhere we turn—whether in advertisements, grocery store aisles, or on social media—we encounter terms like “probiotic” and “prebiotic”. As our understanding of the role beneficial microbes play in gut health has evolved, new terminology has emerged, including next-gen probiotic, postbiotics, paraprobiotics, and metabiotic. But what do these terms mean? How do they differ from one another, and what do they share in common?

Probiotics

Probiotics are defined as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host” [3]. In simple terms, probiotics are beneficial live microorganisms.

Originally recognized for their effects on digestive health, research now shows that probiotics have a broader impact, [4, 5], influencing immune, vaginal, metabolic, skin, and even mood health.

Most probiotics on the market today contain lactic acid bacteria strains, such as lactobacilli and bifidobacteria, which are generally recognized as safe due to their long history of consumption. These are what we refer to as “traditional probiotics”.  In the past 15 years, however, the concept of next-generation probiotics has emerged. New strains like Akkermansia muciniphila, Veillonella spp., and Eubacterium halii have entered the scene, identified by comparing the gut microbiota of healthy versus sick individuals to address specific health needs [6]. Despite their differences, both traditional and next-generation probiotics share the same core definition: they must confer a health benefit.

Prebiotics

Prebiotics serve as food for beneficial microorganisms. By definition, they are “substrates that are selectively utilized by host microorganisms to confer a health benefit” [7]. The fundamental aspect of a prebiotic is its ability to selectively stimulate the growth and activity of “good” microorganisms. The non-digestible nature of prebiotic fibers and compounds allow them to reach the gut and nourish these beneficial microbes. While some prebiotics are fibers, not all fibers are prebiotics, and vice versa. Understanding this distinction is key to supporting gut health.

Common prebiotics include inulin, fructooligosaccharides (FOS) and galactooligosaccharides (GOS). Other compounds like polyphenols, conjugated linoleic acid (CLA), polyunsaturated fatty acid (PUFAs), mannanoligosaccharide (MOS), and xylooligosaccharide (XOS) also function as prebiotics. Human milk oligosaccharides (HMOs) have gained popularity, especially in infant nutrition.

When a prebiotic is combined with a probiotic, the result is a synbiotic—written with an ’n’ and not an ’m’.  A synbiotic is defined as “a mixture comprising live microorganisms and substrate(s) selectively utilized by host microorganisms that confer a health benefit”. The prebiotic can enhance the growth or activity of either the gut microorganism or the probiotic itself [8].

Postbiotics

The latest addition to the “biotics” family is the postbiotic. This category includes parabiotics, metabiotics, para-psychobiotics, killed probiotics, and non-viable probiotics.  A postbiotic is defined as “a preparation of inanimate microorganism and/or their components that confer a health benefit on the host” [9]. While probiotics are alive, postbiotics are their non-living counterparts.

Interest in postbiotic has surged due to their stability and versatility in various applications, including supplements, food products, and beverages, without the challenge of maintaining live microorganisms throughout a product’s shelf life.

Although the science surrounding postbiotics is newer than that of pro or prebiotics, research has shown that they support digestive and immune health, with benefits extending beyond the gut [10].

Conclusion

The gut microbiota plays a pivotal role in shaping our health, leading to increased interest in “biotics” as a means of supporting it. The various terms—probiotics, prebiotics, synbiotics, and postbiotics—can be confusing. However, they all share a common goal: to provide health benefits to consumers. It is important to acknowledge that not all pro/postbiotic strains or prebiotic compounds offer the same benefit. Some may support digestive health, while others focus on immune function. For instance, a probiotic for digestive health may alleviate constipation, while another helps reduce diarrhea frequency. This is why selecting a “biotic” tailored to specific health needs is essential. To make the right choice, look for science-backed products.

References

1. Gilbert, J.A., et al., Current understanding of the human microbiome. Nat Med, 2018. 24(4): p. 392-400.
2. Hou, K., et al., Microbiota in health and diseases. Signal Transduct Target Ther, 2022. 7(1): p. 135.
3. Hill, C., et al., Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol, 2014. 11(8): p. 506-14.
4. Lehtoranta, L., et al., Healthy Vaginal Microbiota and Influence of Probiotics Across the Female Life Span. Front Microbiol, 2022. 13: p. 819958.
5. Markowiak, P. and K. Slizewska, Effects of Probiotics, Prebiotics, and Synbiotics on Human Health. Nutrients, 2017. 9(9).
6. Abouelela, M.E. and Y.A. Helmy, Next-Generation Probiotics as Novel Therapeutics for Improving Human Health: Current Trends and Future Perspectives. Microorganisms, 2024. 12(3).
7. Gibson, G.R., 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, 2017. 14(8): p. 491-502.
8. Swanson, K.S., et al., The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of synbiotics. Nat Rev Gastroenterol Hepatol, 2020. 17(11): p. 687-701.
9. Salminen, S., et al., The International Scientific Association of Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of postbiotics. Nat Rev Gastroenterol Hepatol, 2021. 18(9): p. 649-667.
10. Mosca, A., et al., The clinical evidence for postbiotics as microbial therapeutics. Gut Microbes, 2022. 14(1): p. 2117508.