New research in the lab suggests that drinking dark-coloured grapes, whether in red wine or juice, could help people better manage obesity and other metabolic disorders, such as fatty liver disease.
Obviously it's important to note that binge drinking red wine, or juice for that matter, isn't going to do anything great for your liver or your waist line. But molecular biologists from Oregon State University in the US have found that a chemical in red grapes called ellagic acid helps human liver cells better metabolise fatty acids, and also slows down the growth of existing fat cells.
The team, led by biochemist and molecular biologist Neil Shay, grew human liver and fat cells in the lab, and then exposed them to extracts of four natural chemicals that are found in muscadine grapes - a type of dark red grape that's often used in red and desserts wines, as well as jams and juices.
They found that ellagic acid in particular was effective at slowing the growth of new and existing fat cells, as well as helping the liver cells to burn fat better.
This doesn't mean that the red grapes are some kind of miracle weight loss therapy, but it does mean that they may be able to help boost fat burning, particularly in the liver.
"We didn't find, and we didn't expect to, that these compounds would improve body weight," said Shay in a press release. "But by boosting the burning of fat, especially in the liver, they may improve liver function in overweight people."
"If we could develop a dietary strategy for reducing the harmful accumulation of fat in the liver, using common foods like grapes," he added, "that would be good news."
These in vitro results, which have been published in the Journal of Nutritional Biochemistry, back up the results of a 2012 study that Shay and colleagues conducted on lab mice - where they either fed mice a normal diet made up of around 10 percent fat, or meals comprised of 60 percent fat.
"Our mice like that high-fat diet and they over-consume it," said Shay in the release. "So they're a good model for the sedentary person who eats too much snack food and doesn't get enough exercise."
Half of the high-fat mice then had their diets supplemented with extracts from Pinot noir grapes - the equivalent human dose would be around one and a half cups of grapes a day.
Over a 10-week trial, the mice that were fed the high-fat diet developed fatty livers and diabetic symptoms. But those that had been given grape extract had less fat accumulated in their livers, and had lower blood sugar than the mice that consumed the high-fat diet alone.
In fact, the mice that ate grapes every day had blood sugar levels comparable to those seen in the lean, healthy mice that had been fed the healthy diet.
They're not yet sure how the grape extract could help burn fat, but in the 2012 study the team found that two proteins, PPAR-alpha and PPAR-gamma, that work within cells to metabolise fat and sugar were working harder in the tissue of the overweight mice that were fed the grapes.
Shay hypothesises that the ellagic acids in the grapes are binding to the receptors of these proteins, causing them to switch on the genes that burn dietary fat and glucose - this is a similar pathways that many prescribed drugs use to lower blood sugar.
They now hope to test further exactly how the ellagic acids work in our cells. But Shay stresses he isn't planning to replace medication, simply offer consumers some simple and cheap ways to boost their metabolic function.
"We are trying to validate the specific contributions of certain foods for health benefits," said Shay in the release. "If you're out food shopping, and if you know a certain kind of fruit is good for a health condition you have, wouldn't you want to buy that fruit?"
And while we're on the topic, just last week, another team of researchers found that a separate compound in red grapes may help to delay age-related memory decline. We know it's early days, but we're feeling pretty good about having a (small) glass of red wine with dinner.