Prebiotic potential of polyphenols, its effect on gut microbiota and anthropometric/clinical markers: A systematic review of randomised controlled trials

Background: Polyphenols have been implicated to have numerous health benefits, and much of these are attributed to the metabolism of phenolic compounds by gut microbiota. The aim of this systematic review was to examine the effects of polyphenol consumption in modulating gut microbiota and anthropometric variables/clinical markers in randomised controlled trials (RCTs). Scope and approach: We systematically searched PubMed, Scopus, Embase, Cochrane library and Web of Science databases from inception to31^st July 2019 following the PRIMSA guidelines.RCTs reporting on the effects of polyphenol consumption on gut microbes, and anthropometric variables (body weight, BMI, waist circumference, hip circumference)/clinical markers (CVD markers, and colon cancer markers) were included in this review. The methodological quality of the studies was assessed using the Cochrane Collaboration's risk of bias tool and Jadad scale. Key findings and conclusion: Seventeen RCTs met the inclusion criteria. Ten studies highlighted significant changes in the microbial profile, while 15 reported significant changes in CVD and colon cancer markers. The univariate correlation data showed a significant correlation between certain genera with clinical markers, specifically TNFα, cholesterol, HDL, CRP, and LPS. In the multivariate analysis, negative correlations were reported between Lactobacillus and TAG, CRP, Bacteroides with TAG, HDL, DBP, and SBP, and Bifidobacterium with cholesterol and CRP. This review supports the notion of polyphenols as prebiotics as significant modulation of intestinal microbes affecting mainly CVD markers were found in most of the RCTs. Further well-structured trials with larger sample size, longer duration, and high-throughput molecular techniques, will provide more conclusive results. Protocol registration number: PROSPERO; CRD42017077577;