Red wine is a potent source of antidiabetic compounds – but they might not get past your gut. The finding is sure to enliven the ongoing debate over the drink's health benefits.
Alois Jungbauer and colleagues at the University of Natural Resources and Life Sciences in Vienna, Austria, tested 10 reds and two whites to find out how strongly the wines bound to a protein called PPAR-gamma, which is targeted by the antidiabetic drug rosiglitazone. (This drug is marketed under the brand name Avandia). PPAR-gamma is a type of protein called a receptor. Among other things, it regulates the uptake of glucose in fat cells. Rosiglitazone targets PPAR-gamma in fat cells to make them more sensitive to insulin and improve the uptake of glucose. It is used as a treatment for type 2 diabetes, a condition where people either do not make enough insulin to keep their body's glucose levels down, or become resistant to normal insulin levels.
Several studies have shown that moderate consumption of red wine can reduce the risk of type 2 diabetes. So Jungbauer and colleagues determined the wines' binding affinity for PPAR-gamma and compared the results with the effects of rosiglitazone. They found that the white wines had low binding affinities, but all the reds bound readily: the tendency of 100 millilitres of red wine – about half a glass – to bind to PPAR-gamma is up to four times as strong as the same tendency in the daily dose of rosiglitazone.
"It's incredible. It's a really high activity," says Jungbauer. "At first we were worried it was an artefact, but then we identified the compounds responsible in the wine." The flavonoid epicatechin gallate – which is also present in green tea – had the highest binding affinity, followed by the polyphenol ellagic acid, which comes from the oak barrels the wine is kept in. The researchers think that some of the antidiabetic activity of red wine could be due to these compounds activating PPAR-gamma.
But Jungbauer warns that these compounds don't make red wine a magic bullet. The compounds in a glass of wine may have other antidiabetic effects and in any case, not all of the compounds will be absorbed and available to the body to use. "Wine also contains ethanol, which will add to your calories," he says. Véronique Cheynier, research director at the department of oenology at the University of Montpellier 1, France, says that most polyphenols do not pass through the digestive tract unchanged and may not be absorbed at all.
The next step for Jungbauer and his team will be to measure the metabolic effects of the wine compounds on healthy people. Jungbauer stresses that moderate consumption is the key to health benefits from wine. "It is important to limit the intake of wine. Obesity is one of the major problems of our society," he says.
Paras Mishra of the University of Louisville, Kentucky, who was not involved in the study, warns that drinking too much wine "could be bad even in diabetes".