The byproduct is called grape pomace, describing the solid remains of grapes after the mass has been pressed for its liquid.
“The in vivo regulation of targeted micro RNAs related to glucose metabolism observed following grape pomace extract consumption suggests a possible role of grape pomace on glucose metabolism, which would contribute to decrease the risk of type 2 diabetes,” the authors maintained.
They also found a significant decrease in blood fasting glucose levels after the 21-day supplementation period.
“In summary, [grape pomace] can be considered a promising functional ingredient for health promotion and disease prevention,” they added.
Their paper was published this summer in the Journal of Functional Foods. It was written by researchers in Spain and funded by the Spanish Ministry of Economy and Enterprise. The outcomes can be a potential breakthrough for the world's largest wine producing countries (Spain ranks second as of 2014 based on FAO data), both as a potential revenue stream for its vintners and as a way to manage and reduce waste.
Grape pomace used in the study was a branded ingredient called Eminol, produced by Spanish company Abrobiotec.
Studies on grape pomace still lacking
“Grape pomace has shown attractive health-promoting activities in vitro, but little efforts have been made until now to translate this work into humans,” the researchers argued.
They added that the present pilot intervention is the first to investigate grape pomace’s effects in general host biological and physiological parameters and impact on the composition and metabolic activity of the gut microbiota.
No effect on microbiota
Originally, the researchers wanted to analyze how the polyphenols in grape pomace may interact with the study participants’ gut bacteria.
They built this hypothesis based on previous studies that have posited a prebiotic effect of polyphenols found in fruits like grapes. One such study they cited was published in 2012, in which researchers found that grape antioxidant dietary fiber stimulated Lactobacillus growth in rats.
But in this present study, the researchers did not find any significant changes in fecal bacterial populations or in the content of fecal and urine phenolic metabolites.
Ten healthy women aged 25 to 65 years completed the study. Some requirements for enrollment included no antibiotic, prebiotic, probiotic, or vitamin supplement consumption in the six months before the start of the study.
Participants went through a washout period of 10 days during which they maintained a low-polyphenol diet, called the ‘washout period.’ After that, all participants ingested two capsules of the grape pomace a day, totaling to 1400 mg per day, at breakfast, over 21 days.
Researchers extracted blood samples from the participants after an overnight fast at three points: The beginning of the study after the washout period, after 14 days of consumption of the supplement, and at the end of the supplement intervention at day 21.
The study was not placebo-controlled, which was one limitation. The sample size of participants was also small.
“Future studies are needed if these results are to be extended to subjects with diabetes,” the authors wrote.
Source: Journal of Functional Foods
Published online ahead of print, https://doi.org/10.1016/j.jff.2018.03.031
“Supplementation with grape pomace in healthy women: Changes in biochemical parameters, gut microbiota and related metabolic biomarkers”
Authors: Irene Gil-Sanchez, et al.