A team of Danish researchers who reviewed several trials on probiotic supplements say they found “no convincing evidence” that the products changed the composition of faecal bacteria in healthy adults.
Oluf Pedersen, who led the research at the University of Copenhagen, said: “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.”
Pedersen and his team reviewed seven randomised controlled studies that investigated whether a daily probiotic supplement had any effect on the microbial composition of healthy adults’ faeces. The interventions were delivered using three different probiotics strains (or combinations) – lactobacillus, bifidobacterium and lactobacillus combined, or Bacillus – in capsule (4), sachet (1), milk drink (1) and biscuit (1) form.
In a paper published in Genome Medicine, the researchers write: “In terms of richness, evenness, or α-diversity measures, no effects were observed on the fecal microbiota composition in any of the included studies when compared to placebo and only in the study by Ferrario et al. (Lactobacillus paracasei) was it found that probiotic treatment significantly modified the compositional dissimilarity.”
Nadja Buus Kristensen, a joint author of the study, told The Guardian: “According to our systematic review, no convincing evidence exists for consistent effects of examined probiotics on faecal microbiota composition in healthy adults, despite probiotic products being consumed to a large extent by the general population.”
Pedersen added: “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.”