Modifications of gut microbiota after grape pomace supplementation in subjects at cardiometabolic risk: a randomized cross-over controlled clinical trial

Abstract

Polyphenols are dietary bioactive compounds able to induce modifications in the gutmicrobiota profile, although more clinical studies are needed. With this aim, a randomized cross-overclinical trial was conducted, where 49 subjects at cardiometabolic risk (exhibiting at least two metabolicsyndrome factors) were supplemented with a daily dose of 8 g of grape pomace (GP) for 6 weeks,with an equivalent control (CTL) period. The levels of total bacteria and Bacteroidetes, Firmicutes,Lactobacilliales,BacteroidesandPrevotellawere estimated in fecal DNA by quantitative real-timePCR (qPCR), while fecal short-chain fatty acids (SCFAs) were assessed by gas chromatography.Several cardiometabolicmarkers were evaluated in blood samples. GP reduced insulin levels only inhalf of the participants (responders). GP supplementation did not cause significant modifications inthe microbiota profile of the whole group, except for a tendency (p=0.059) towards a decrease inthe proportion of Lactobacilliales, while it increased the proportion ofBacteroidesin non-respondersubjects. The reduction of insulin levels in subjects at cardiometabolic risk upon GP supplementationappears not to be induced by changes in the major subgroups of gut microbiota. Further studies at thespecies level may help to elucidate the possible role of microbiota in GP-induced insulinemic status