A new study by Spanish researchers has found fresh evidence that following the Mediterranean diet, including wine in moderation, can lead to better heart health. The research is notable because it examines how our bodies metabolize the polyphenols found in foods and wine in the diet, and how those polyphenols could be working to help our bodies on a molecular level.
Going molecular
Scientists have long known about the potential health benefits of the Mediterranean diet, which involves consuming mostly fruits, vegetables, seafood, nuts, whole grains and olive oil, as well as moderate amounts of wine. Those benefits are likely thanks, in part, to the diet’s high levels of polyphenols, organic compounds found in fruits, vegetables, chocolate, tea and wine.
But how polyphenols behave in the body remains poorly understood. Studies have found that many polyphenols are quickly broken down. Relatively few of the antioxidants in a kale salad or glass of Cabernet reach the bloodstream in their original form.
Rather than getting absorbed in the small intestine, many polyphenols pass into the colon, where the gut microbiota metabolize them into related compounds. Those microbial polyphenols may have different health effects than their precursor molecules. And that metabolization appears crucial for unlocking their health benefits.
Measuring the impact
In the new study, “Association of Microbiota Polyphenols with Cardiovascular Health in the Context of a Mediterranean Diet,” which was published in January in Food Research International, the researchers analyzed data from the PREDIMED trial, a randomized controlled trial of the Mediterranean diet’s ability to prevent cardiovascular disease in older people. For the new study, the researchers randomly selected 200 participants from PREDIMED’s Barcelona study center and compared the levels of five microbial phenolic metabolites in urine samples with the participants’ adherence to the Mediterranean diet and their cardiovascular health.
They found that people who most consistently followed the Mediterranean diet had the highest levels of microbial polyphenols in their urine, which correlated with improved cardiovascular health. Dr. Rosa Lamuela-Raventós, the study’s lead author, is a professor of nutrition, food science and gastronomy at the University of Barcelona and principal investigator at the Spanish Biomedical Research Centre in Physiopathology of Obesity and Nutrition (CIBEROBN). She told Wine Spectator that the study affirms the Mediterranean diet’s link with good health.
“With this study we observe that people who follow a Mediterranean diet have higher amounts of microbial phenolic metabolites that are associated with better cardiovascular health,” she said. “I believe that the Mediterranean diet is very rich in polyphenols and other bioactive compounds and that the usual fat [used] in the Mediterranean countries, virgin olive oil, helps to increase the bioavailability of [dietary] polyphenols.”
Fab 5 polyphenols
The researchers looked for five specific microbial phenolic metabolites: protocatechuic acid, enterodiol glucuronide, enterolactone glucuronide, urolithin B glucuronide and vanillic acid glucuronide.
Protocatechuic acid is found in wine, especially white wine, and has been linked to improved bone mineral density in older women, among other potential benefits. Higher levels of urolithin B glucuronide were strongly associated with lower LDL (“bad”) cholesterol. Urolithins are found in significant amounts in walnuts, pomegranates and oak-aged red wines.
Limitations
The study examined the effects of the Mediterranean diet as a whole, not wine specifically. And while wine made up most of the alcohol consumption among PREDIMED participants, the study did not differentiate between types of alcohol consumed or link wine consumption with any particular health outcomes. And there are many other microbial polyphenols that may influence health that the study did not focus on.
Just as wine is only one part of the Mediterranean diet, the researchers suggest that microbial polyphenols appear to improve heart health when acting as a team: “Notably, individual microbial phenolic metabolites did not seem to benefit overall [cardiovascular health], suggesting that the phenolic metabolites may have a positive impact on cardiovascular health in combination rather than individually.”
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