Consumption of red wine increases gut health, based on α-diversity of the intestinal microbiome, researchers report in the January 2020 issue of Gastroenterology. White wine had only weak effects, whereas beer, cider, spirits had none. The researchers propose that even infrequent red wine consumption benefits gut health, possibly via effects of polyphenols on intestinal microbes.
Red wine production includes the skin of the grapes, resulting in nearly a 10-fold higher content of polyphenols than white wine. Consumption of red wine polyphenols has been previously associated with health benefits ranging from reducing cardiovascular disease risk factors, metabolic syndrome, and depression to improving cognition. The effects of polyphenols are believed to involve effects on intestinal microbes.
Red wine polyphenols include flavonoids (anthocyanins and flavan-3-ols), nonflavonoids (stilbenes), gallic acid, oligomeric and polymeric proanthocyanins, catechins, and phenolic acid, which can reduce oxidative stress and expand beneficial gut bacteria. Caroline I. Le Roy et al studied the effect of various alcoholic drinks on intestinal microbiomes and health outcomes of 3 large population cohorts.
Le Roy et al compared the effects of beer and cider, red wine, white wine, spirits, and sum of all alcohols on the α-diversity of the intestinal microbiota (determined from 16s ribosomal RNA sequence data) in discovery cohort of 916 women (from a study of twins in the United Kingdom) and 2 replication cohorts (in Europe and North America) using a linear mixed-effect model adjusted for age, body mass index, Healthy Eating Index scores, education, and family structure. Alcohol consumption was determined from food frequency questionnaires, which reported the average number of glasses of alcohol consumed monthly.
LeRoy et al found that red wine consumption was associated, in a frequency-dependent manner, with α-diversity—even rare consumption had an effect. White wine was associated with α-diversity to a lesser extent, and there was no association with other alcohol categories.
The twin members who drank red wine at a frequency at least 2 categories above their co-twins had significantly higher α-diversity. In fact, the red-wine drinkers had significantly greater α-diversity than non–red wine drinkers in all 3 cohorts analyzed.
Furthermore, α-diversity was a potential partial mediator of the negative association between red wine consumption and body mass index or levels of chylomicrons (lipoprotein particles in blood). LeRoy et al also observed a direct association between red wine consumption and blood level of insulin and high-density lipoprotein.
The authors conclude that even rare consumption of red wine is sufficient to increase α-diversity of the intestinal microbiome, which might contribute to some but not all of the debated health benefits of red wine, such as increased cholesterol metabolism and reduced adiposity. This might be related to the high content of polyphenols in red wine, such as anthocyanin, resveratrol, and gallic acid. Resveratrol has been proposed protect against fat accumulation by inhibiting lipogenesis and increasing insulin-mediated uptake of glucose. The proportion of Barnesiella, which supports the immune system, was higher in microbiota of red-wine consumers, consistent with findings from studies of rats.
The study was limited by self-reported alcohol consumption (often underestimated), and the fact that body mass index was the only common health surrogate available from all the cohorts. Furthermore, this was a cross-sectional and observational study; randomized studies would be needed to determine whether red wine drinking has direct effects on composition of the intestinal microbiome and health outcomes.
In an editorial that accompanies the article, Nenad Naumovski et al state that although it is clear that modifications to the gut microbiota can affect health, there are challenges to studying the specific effects of red wine polyphenols. One challenge is the diversity of consumed wines and their polyphenol content (see Figure). Another is that high consumption of alcohol has many adverse health effects, including development of cirrhosis. So, it remains to be determined whether long-term trials of red wine can be safely managed in an ethically responsible manner. It will be important to identify doses that provide beneficial health effects without reducing gut barrier integrity.