With the huge amount of press coverage of the effectiveness of probiotics and prebiotics as a way to improve human health and wellbeing, it’s difficult to keep abreast of everything that’s going on in the field.
A recent narrative review, authored by five of the world’s leading scientists in the field, summarizes the clinical application and use in humans of prebiotics and probiotics, including the mechanisms that drive their benefits for host health and future goals.
In terms of diet and their effect on health, prebiotics and probiotics are the most closely studied gut microbiota-targeted tools. Strains of Lactobacillus, Bifidobacterium and Saccharomyces have a long history of safe and effective use as probiotics. And the clinical benefits of probiotics in pediatric and adult populations can be seen in the following conditions:
The prophylactic and therapeutic effects of probiotics on these conditions can be mediated by modifying the gut microbiota composition or its function. This is done by involving antimicrobial production and cross-feeding and substrate transformation for other commensal microorganisms, which has been one of the most widely studied means by which probiotic microorganisms act.
Other probiotics mechanisms of action are also plausible and include interaction with host cells (e.g. modulating the immune system and improving intestinal barrier integrity), colonization resistance, and the formation of enzymes and neurochemicals.
In fact, probiotics may act through a wide range of mechanisms that are not necessarily related to a direct effect on the resident microbiota. This means that if a probiotic doesn’t colonize the human digestive tract, that doesn’t mean it is ineffective.
So what does the future hold? On the horizon lies the promise of newly constructed recombinant strains and next-generation candidate probiotics, which include Roseburia, Akkermansia, Propionibacterium and Faecalibacterium species.
As for prebiotics—defined as substrates that are selectively utilized by host microorganisms, conferring a health benefit—both glucans and fructans have shown their health benefits.
Nevertheless, the evidence for prebiotic intervention is weaker than that reported for probiotics. Two of the most closely studied prebiotic indications include the protection of formula-fed infants against infections when administered in infant formulas and improved bowel function in healthy adults.
The mechanisms of action by which prebiotics might confer health benefits have been tested via in vitro and animal models and include: defense against pathogens, immune modulation, increased mineral absorption, improved bowel function, metabolic effects and effects on satiety.
Other substrates such as polyphenols and polyunsaturated fatty acids might exert prebiotic effects and therefore show promise for the future. Promising outcomes of prebiotic application also include increased satiety, reduced energy intake and body fat mass, and improved post-prandial glucose responses.
In addition, the authors mention prebiotics and probiotics’ applications beyond their gut-derived effects, including in the oral cavity, the vaginal tract and on skin. And consumption of vegetables rich in inulin-type fructans is associated with increased satiety and fewer cravings for sweet and salty foods in healthy adults.
A key take-home message from the authors is that the use of prebiotics and prebiotics by healthcare professionals and consumers should be evidence-based—preferably from randomized trials. As not all products have been validated and gut microbiota differences don’t imply that modification will lead to improved health, it is important to keep updated on their clinical application and use, with any decisions supported by reliable research.
In addition, the authors highlight that research in the field should move from traditional probiotics to new targets (e.g. anti-adhesive molecules) and beneficial gut bacteria that aren’t used nowadays as probiotics (e.g. butyrate-producers). Although the increased use of high-throughput sequencing technologies is widely used, considering the overall functional potential of the microbiome assessed by transcriptomic, metabolomic and proteomic analysis will also optimize clinical translation of the role of targeting gut microbiota for improving health.
Sanders ME, Merenstein DJ, Reid G, et al. Probiotics and prebiotics in intestinal health and disease: from biology to the clinic. Nat Rev Gastroenterol Hepatol. 2019. doi: 10.1038/s41575-019-0199-6.
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