Posted 11 May 2016
From The Guardian
Fans of probiotic drinks and foods may be wasting their money, according to a review of current research into the supplements that suggests they may be of no benefit to healthy adults.
A Danish team looked at the results of seven trials of the products – often sold as milk-based drinks, biscuits, sachets, or capsules – and found no evidence they changed the composition of faecal bacteria in healthy adults.
Online blogs and magazines have helped spur a trend for lacto-fermentation of foodstuffs by touting a range of purported health benefits, such as improved digestion and resistance to infections.
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.”
In-depth clinical trials would be needed to explore whether probiotics can help people avoid getting sick, he added.
Probiotics are live microbial food ingredients – sometimes labelled “friendly bacteria” – that are said to provide the consumer with numerous health benefits by improving the intestinal microbial balance. They are often made by introducing live bacterial cultures to everyday foodstuffs, which metabolise sugars as they multiply and leave them with a sour, fresh flavour. Aside from branded products specifically marketed as probiotic supplements, such foods include plain yoghurt, sauerkraut, miso and kefir.
Advocates claim they can help with digestive health, allergies, immune response and obesity. Previous research has suggested that in some cases, such as where diarrhoea has arisen from antibiotic use, probiotics can have a therapeutic effect.
But when 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, only one showed significant changes.
Studies included in the review had sample sizes ranging from 21 to 81, and included participants aged 19 to 88 years old. The Copenhagen team noted that the real impact of the probiotics may have been masked by small sample sizes and the use of different strains of bacteria and variations in participants’ diets, among other factors.
Pedersen said: “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.”
Their findings are published in the online journal Genome Medicine.
Alterations in fecal microbiota composition by probiotic supplementation in healthy adults: a systematic review of randomized controlled trials
- Nadja B. Kristensen
- Thomas Bryrup,
- Kristine H. Allin,
- Trine Nielsen,
- Tue H. Hansen and
- Oluf Pedersen
© Kristensen et al. 2016
Received: 15 January 2016
Accepted: 8 April 2016
Published: 10 May 2016
The effects of probiotic supplementation on fecal microbiota composition in healthy adults have not been well established. We aimed to provide a systematic review of the potential evidence for an effect of probiotic supplementation on the composition of human fecal microbiota as assessed by high-throughput molecular approaches in randomized controlled trials (RCTs) of healthy adults.
The survey of peer-reviewed papers was performed on 17 August 2015 by a literature search through PubMed, SCOPUS, and ISI Web of Science. Additional papers were identified by checking references of relevant papers. Search terms included healthy adult, probiotic, bifidobacterium, lactobacillus, gut microbiota, fecal microbiota, intestinal microbiota, intervention, and (clinical) trial. RCTs of solely probiotic supplementation and placebo in healthy adults that examined alteration in composition of overall fecal microbiota structure assessed by shotgun metagenomic sequencing, 16S ribosomal RNA sequencing, or phylogenetic microarray methods were included. Independent collection and quality assessment of studies were performed by two authors using predefined criteria including methodological quality assessment of reports of the clinical trials based on revised tools from PRISMA/Cochrane and by the Jadad score.
Seven RCTs investigating the effect of probiotic supplementation on fecal microbiota in healthy adults were identified and included in the present systematic review. The quality of the studies was assessed as medium to high. Still, no effects were observed on the fecal microbiota composition in terms of α-diversity, richness, or evenness in any of the included studies when compared to placebo. Only one study found that probiotic supplementation significantly modified the overall structure of the fecal bacterial community in terms of β-diversity when compared to placebo.
This systematic review of the pertinent literature demonstrates a lack of evidence for an impact of probiotics on fecal microbiota composition in healthy adults. Future studies would benefit from pre-specifying the primary outcome and transparently reporting the results including effect sizes, confidence intervals, and Pvalues as well as providing a clear distinction of between-group and within-group comparisons.
Read the full study here