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Making Sense of Pre-, Pro- and Synbiotics

When it comes to therapeutic implications of the gut microbiome, the currently available pre-, pro- and synbiotics only represent the tip of the iceberg.

By Purna Kashyap, MBBS, scientific advisory board member, AGA Center for Gut Microbiome Research and Education


Probiotics are live microorganisms that, when given in sufficient amounts, are expected to confer a health benefit on the host. In general, probiotics have been shown to have beneficial effects on human health in a range of clinical studies. However, it is difficult to compare effectiveness between these studies because key variables are not examined in a standardized way; heterogeneity in strains of bacteria, type of physiological effect, sample size and study population, formulations, dosage and duration of therapy all make it difficult to draw definitive conclusions. Nevertheless, the outlook is optimistic as there appears to be a trend towards benefit. The significant advancement in our understanding of the role of microbiota in disease states has inspired the development of next generation of probiotics, including genetically engineered strains that are more targeted and disease specific.


In contrast, “prebiotics” originally referred to any selectively fermented ingredient that led to a targeted increase in specific microbes, thus conferring a health benefit. However, the definition of a prebiotic has evolved over time. A more timely and accurate definition of a prebiotic is “a nondigestible compound that, through its metabolization by microorganisms in the gut, modulates composition and/or activity of the gut microbiota thus conferring a beneficial physiological effect on the host.” This updated definition decreases the emphasis on selectivity and increases the focus on the effect on the microbial community, creating a requirement for a beneficial effect on the host organism (e.g., humans). It also allows for expansion of putative candidate prebiotics beyond traditional oligosaccharide (fructo- and galacto-olisaccharides and inulin) to include non-carbohydrates as well as more complex carbohydrates (starch, whole grains).


There is also a growing interest in synbiotics, which are in essence a combination of a prebiotic and a probiotic. Synbiotics are meant to enhance the efficacy of a probiotic by including a prebiotic that is thought to specifically support the growth of the probiotic bacteria or, alternately, has a favorable effect on the overall gut microbial community. While in theory this appears to be a reasonable strategy, overall the clinical data are sparse and don’t yet show a definitive advantage over probiotics alone. This will likely change as we improve our current generation of pro and prebiotics.


The currently available pre-, pro- and synbiotics only represent the tip of the iceberg. The therapeutic implications of the microbiome are yet to be fully realized, so hold tight.


Recommended Reading


    • Hill, C., Guarner, F., Reid, G. 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;11:506-514.





This article is part of the AGA Microbiome Update, delivered via email to AGA members on Tuesday, Aug. 1.