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 gut microbiota profile, although more clinical studies are needed. With this aim, a randomized cross-over clinical trial was conducted, where 49 subjects at cardiometabolic risk (exhibiting at least two metabolic syndrome 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, Bacteroides and Prevotella were estimated in fecal DNA by quantitative real-time PCR (qPCR), while fecal short-chain fatty acids (SCFAs) were assessed by gas chromatography. Several cardiometabolic markers were evaluated in blood samples. GP reduced insulin levels only in half of the participants (responders). GP supplementation did not cause significant modifications in the microbiota profile of the whole group, except for a tendency (p = 0.059) towards a decrease in the proportion of Lactobacilliales, while it increased the proportion of Bacteroides in non-responder subjects. The reduction of insulin levels in subjects at cardiometabolic risk upon GP supplementation appears not to be induced by changes in the major subgroups of gut microbiota. Further studies at the species level may help to elucidate the possible role of microbiota in GP-induced insulinemic status.

Polyphenols as modulators of pre‐established gut microbiota dysbiosis: State‐of‐the‐art

“…Subjects at cardio‐metabolic risk (with at least two metabolic syndrome factors) were supplemented with a daily dose of 8 g of grape pomace for 6 weeks. Grape pomace was found to reduce insulin levels only in the half of the participants (named responders), tended to reduce the order Lactobacillales in both responders and nonresponders, but increased Bacteroides only in nonresponders 73 . In this study there is no evaluation of the microbiota at the species level, quantitative real‐time PCR was used instead of next‐generation sequencing techniques; furthermore, the lack of the placebo, it made impossible to establish whether the observed effects depended on the high fiber or the polyphenol content of the grape pomace.…”

“…Grape pomace was found to reduce insulin levels only in the half of the participants (named responders), tended to reduce the order Lactobacillales in both responders and nonresponders, but increased Bacteroides only in nonresponders. 73 In this study there is no evaluation of the microbiota at the species level, quantitative real‐time PCR was used instead of next‐generation sequencing techniques; furthermore, the lack of the placebo, it made impossible to establish whether the observed effects depended on the high fiber or the polyphenol content of the grape pomace. The study of Vetrani and colleagues 85 evaluated the effects of a diet rich in polyphenols or a combination of polyphenols and long‐chain n − 3 polyunsaturated fatty acids on the gut microbiota of individuals at high cardio‐metabolic risk.…”

Potential Relationship between the Changes in Circulating microRNAs and the Improvement in Glycaemic Control Induced by Grape Pomace Supplementation

“…At the end of the experimental period, 23 participants were classified as responder subjects and 26 as nonresponders, based on a decrease in fasting insulin ≥10% [21]. Although the level of glucose remained unchanged, a strong reduction in insulin level was found in responder subjects (−40%) and, as a consequence, HOMA-IR was also significantly reduced [22]. GP was obtained from Vitis vinifera L., cv Tempranillo freshly collected at the moment of wine devatting (Roquesan Wineries, Quemada, Burgos, Spain).…”

Grape Pomace Extract Attenuates Inflammatory Response in Intestinal Epithelial and Endothelial Cells: Potential Health-Promoting Properties in Bowel Inflammation

“…These dietary polyphenols were able to attenuate endothelial dysfunction and reduce leukocyte adhesion to the endothelium [ 26 , 27 ]. Moreover, recent evidence reports grape pomace to improve the gut microbiota by increasing the beneficial bacteria and decreasing the harmful bacteria, as well as reducing the level of pro-inflammatory cytokines [ 19 , 28 ]. However, the biological health potential of grape pomace-derived polyphenols on intestinal and vascular inflammation and the underlying mechanisms of action are not entirely clear.…”