Do probiotics have a beneficial effect on healthy adults?

Probiotics, also known as ‘good’ or ‘helpful’ bacteria, are often said to be useful for your digestive system. But how advantageous is it to ingest products that contain these probiotics? Published today in Genome Medicine is an article investigating whether probiotics really are beneficial to healthy individuals. Oluf Pedersen reveals more.

According to a recent report the global market for probiotics is expected to reach USD 52.35 billion by 2020. Keeping a strong immune system is related to gut health so growing consumer awareness regarding gut health has pushed the demand for these products.

Products are being marketed by alluding to effects on gastrointestinal health and the fecal microbial community.Yet there is little evidence to support any consistent effect of probiotics on the gut microbiota of healthy individuals, as recorded in our systematic review just published in the open access journal Genome Medicine.

What we set out to investigate

Our review study here at the Novo Nordisk Foundation Center for Basic Metabolic Research in Copenhagen took a systematic and critical approach to the analysis of seven randomized controlled trials (RCTs) investigating the effect of probiotic products on the fecal microbiota of healthy adults.

We found that no convincing evidence exists for consistent effects of examined probiotics on fecal microbiota composition in healthy adults

We found that no convincing evidence exists for consistent effects of examined probiotics on fecal microbiota composition in healthy adults, despite probiotic products being consumed to a large extent by the general population.

We therefore investigated RCTs for reported effects of probiotics on the overall structure of the fecal microbiota of healthy adults, including the number of species present, the evenness (distribution of species within the populations) and whether the probiotics groups of study participants as a result of the intervention had different changes in bacteria living in their gut than the placebo groups.

What did we find?

Our research found that of the seven original RCTs included in the study, only one observed significantly greater changes in the bacterial species composition of the fecal microbiota in individuals who consumed probiotics compared to those who did not.

Previous research has suggested an unbalancing effect of common disorders like obesity, diabetes, or colorectal cancer on the fecal microbiota and the therapeutic effects of probiotics have been studied in many diseases.

Our research found that of the seven original RCTs included in the study, only one observed significantly greater changes

Yet, while evidence of their effectiveness in metabolic and gastrointestinal disorders can be measured for example against body mass index, insulin resistance or the severity of gastrointestinal symptoms, measuring the effect of probiotics in healthy individuals is more difficult, according to the authors. Also, an international consensus on what defines a normal or healthy fecal microbial community is lacking.

Work for the future

While there is some evidence from previous reviews that probiotic interventions may benefit those with disease-associated imbalances of the gut microbiota, there is little evidence of an effect in healthy individuals.

To explore the potential of probiotics to contribute to disease prevention in healthy people there is a major need for much larger, carefully designed and carefully conducted clinical trials. These should include ideal composition and dosage of known and newly developed probiotics combined with specified dietary advice, optimal trial duration and relevant monitoring of host health status.

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