Grape polyphenols helped offset some of the adverse health consequences of consuming a high fat diet rich in saturated fat, according to two laboratory studies conducted at the University of North Carolina Greensboro, and published recently in the Journal of Nutritional Biochemistry.
In the first study, the researchers found that consuming a high butter-fat diet (33% of energy from fat) enriched with 3% grapes for 11 weeks had a lower percentage of overall body fat and reduced subcutaneous fat deposits. These reductions in body fat were positively associated with changes in intestinal microbes and health; e.g., increases in some beneficial bacteria, decreases in some less desirable bacterial strains, increases in microbial diversity, and improved gut barrier function.
In the second study which ran for 16 weeks, the researchers used an even higher fat diet (44% of energy from fat ) with multiple types of saturated fat, including lard, beef tallow, shortening, and butter similar to some Western-type diets. They investigated the impact of the high fat diet enriched with extracts of either the polyphenol fraction of grapes or the non-polyphenol portion of grapes, as well as the high fat diet plus 5% whole grapes. All the high fat experimental diets were matched for sugar type and amount.
The results showed that the high-fat diet combined with grape polyphenols reduced the percentage of body fat, subcutaneous and visceral fat depots, markers of inflammation in the liver and fat depots, and improved glucose tolerance and intestinal barrier function. While the 5% whole grape diet did not improve the metabolic profile in this second study, it did improve markers of intestinal health; e.g., increased microbial diversity and decreased abundance of several deleterious bacteria in the intestinal tract.
Obesity affects approximately one-third of the adult population in the U.S. and is associated with inflammatory conditions that disrupt the metabolic process and can lead to metabolic syndrome. Gut microbes are thought to play a role in the development of metabolic syndrome; e.g., obesity is associated with a decrease in microbial diversity and impaired barrier function in the intestinal tract.
"These two studies suggest that grapes and grape polyphenols may help offset a number of the adverse effects of consuming a high fat diet and trigger improvements in intestinal or systemic health," said Michael McIntosh PhD, lead investigator of the study. "This is an exciting area of health that merits further study."
Study 1: Table grape consumption reduces adiposity and markers of hepatic lipogenesis and alters gut microbiota in butter fat-fed mice. Baldwin J et al. Journal of Nutritional Biochemistry. DOI:10.1016/j.jnutbio.2015.08.027. January 2016.
Study 2: A polyphenol-rich fraction obtained from table grapes decreases adiposity, insulin resistance and markers of inflammation and impacts gut microbiota in high-fat-fed mice. Brian Collins, Jessie Hoffman, Kristina Martinez, Mary Grace, Mary Ann Lila, Chase Cockrell, Anuradha Nadimpalli, Eugene Chang, Chia-Chi Chuang, Wei Zhong, Jessica Mackert, Wan Shen, Paula Cooney, Robin Hopkins, Michael McIntosh. Journal of Nutritional Biochemistry. DOI:10.1016/j.jnutbio.2015.12.021. Published online February 25, 2016.