The effects of grape and wine polyphenol consumption on gut microbiota: a systematic review of randomised trials in humans

Dietary polyphenols are plant secondary metabolites, present in wide range of fruits and vegetables. Relatively recently, evidence has accumulated supporting an association of polyphenol consumption with health benefits, including reduced risk of developing cardiovascular disease and cancer. These beneficial effects appear to depend on polyphenol modulation by gut microbiota into a range of phenolic metabolites. Several in vitro and animal models support a contribution of dietary polyphenols to the maintenance of intestinal health via stimulated colonisation by beneficial bacteria; however, results from human trials are scarce. A systematic review was performed evaluating human trials describing the effects of grape and wine polyphenol consumption on gut microbiota. Primary search results of publications in the last 10 years (until October 2016) returned 1080 studies. Only seven randomised controlled trials were identified, with studies involving 132 adult participants consuming polyphenols derived from grapes or wine (from one day to five weeks). Findings from these studies identified the active role of gut microbiota play, in the modulation of dietary polyphenols to phenolic metabolites in the human colon. Furthermore, there was evidence suggesting a supportive role of dietary polyphenols increasing beneficial gastrointestinal bacteria. Human studies in this area are limited and additional research is required to understand the complex relationship between polyphenols and gut microbiota, and their potential effects on human health