Nutrition Notes

The Latest on Red Grape and Gut Microbial Health

Grape (Vitis vinifera) contains proanthocyanidins, flavonols, anthocyanidins, and many other bioactive molecules that have been shown to support human health. Grape seeds and skin are particularly high in bioactive compounds. The constituents in grape have been shown to support cardiovascular health, antioxidative status, metabolic function, and a healthy inflammatory response. Recent research indicates that they may also help support gastrointestinal (GI) health and the gut microbiome

Chronic GI inflammatory states can involve an imbalance in GI microbiota and a reduction in bacterial diversity. This can cause downstream effects due to changes in the number of metabolites from microbes. For instance, species in certain Bacteroides, Lactobacillus, and Clostridium genera have been shown to produce bile acids, tryptophan metabolites, and short-chain fatty acids (SCFAs). These metabolites have been shown to influence intestinal permeability, epithelial repair, cellular differentiation, and barrier integrity. 

Research indicates that polyphenols may support a healthy gut microbiome. An estimated 90% of dietary polyphenols are not digested in the small intestine and may therefore influence microbiota in the colon. They have been shown to support healthy populations of certain beneficial bacteria such as Bifidobacterium and Lactobacillus. Certain polyphenols such as resveratrol have also been shown to help support healthy levels of inflammatory cytokines and may help improve microbial dysbiosis. Animal studies have also indicated that certain polyphenols may influence the population of short-chain fatty acid (SCFA)-producing bacteria. SCFAs have been shown to benefit neuronal health by helping modulate nervous system signaling and serotonin release. 

Resveratrol, a molecule found in grape skin, has also been studied for its supportive role in the gut microbiome. Resveratrol has been shown in studies to decrease inducible nitric oxide synthase expression and increase the abundance of Bifidobacterium and Lactobacillus. Supplementation with resveratrol was also shown in animal studies to attenuate the deterioration of colonic wall structure in the presence of colitis. Another animal study reported that relief in colitis symptoms while supplementing with resveratrol may be attributed to observed improvements in microbial dysbiosis and inflammatory markers including interleukin (IL)-6 and IL-17. 

Resveratrol has also been shown to influence the Firmicutes to Bacteroidetes (F/B) ratio. Higher F/B ratios have been linked to increases in the occurrence of certain diseases. Resveratrol and other stilbenoids have been shown in studies to decrease the relative abundance of Firmicutes resulting in decreases in the F/B ratio. 

Animal studies have also indicated that resveratrol may influence the population of SCFA-producing bacteria. One study involved supplementation with resveratrol for eight weeks and reported increases in Lachnospiraceae, Blautia, and Dorea populations which are known to produce butyrate, an SCFA found to support many aspects of human health.

The bioactive constituents in grape may support many aspects of GI health and the gut microbiome. They may also help support metabolic and cardiovascular health and antioxidative status.

By Colleen Ambrose, ND, MAT