If you religiously chug a probiotic drink before leaving the house each morning, you may be in for a surprise.
A new review of studies has found there is "no evidence" to support the idea that probiotics have a beneficial impact for most people.
The study, by researchers at the University of Copenhagen, analysed the findings of seven pervious trials investigating the effect of probiotic products on the general population.
The researchers found that in the majority of cases there was "little difference" to the make up of the gut’s bacteria for healthy people before and after consuming a probiotic product.
Despite this, global sales of probiotic foods, drinks and supplements are predicted to be £29 billion by 2018.
The World Health Organisation currently defines probiotics as "live microorganisms which confer a health benefit to the host if administered in adequate amounts".
However, the latest review of studies has called this definition into question.
The authors investigated the bacterial composition of a group of microorganisms found in faeces.
Of the seven original trials analysed, only one reported significantly greater changes in bacterial make up after probiotics.
Nadja Buus Kristensen, PhD student and junior author, commented: "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."
The seven trials included in the review all included healthy adults between 19 and 88 years of age.
Numbers of individuals in each trial ranged from 21 to 81 and the proportion of women was between 50 and 100%.
Probiotic products were administered as biscuits, milk-based drinks, sachets, or capsules for periods of 21 to 42 days.
The authors of the latest review noted that due to the relatively small sample size, more research is needed before probiotics can be completely dismissed.
Oluf Pedersen, professor at the University of Copenhagen and senior author of the paper 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.
"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."
The NHS currently advises that probiotics may help to reduce bloating and flatulence in some people with IBS.
The latest review is published in full in the the journal Genome Medicine.