Drinking red grape juice or wine in moderation could improve the health of over-weight people by helping them burn fat better, says a study.
The researchers, however, cautioned that the chemicals in the dark-coloured grapes do not promise a miraculous weight-loss.
"We did not expect, and we did not find, these compounds to improve body weight," said Neil Shay, biochemist and molecular biologist at the Oregon State University in the US.
But by boosting the burning of fat, especially in the liver, they may improve liver function in over-weight people.
"If we could develop a dietary strategy for reducing the harmful accumulation of fat in the liver, using common foods like grapes would be good news," Shay added.
The researchers exposed human liver and fat cells grown in the lab to extracts of four natural chemicals found in Muscadine grapes, a dark-red variety native to the south-eastern part of the US.
One of the chemicals, ellagic acid, proved particularly potent: It dramatically slowed the growth of existing fat cells and formation of new ones, and it also boosted the metabolism of fatty acids in liver cells.
In another trial, the researchers supplemented the diets of over-weight mice with extracts from Pinot noir grapes.
Some of the mice were fed a normal diet of "mouse chow" , containing 10 percent fat. The rest were fed a diet of 60 percent fat - the sort of unhealthy diet that would pile excess pounds on a human frame.
Over a 10-week trial, the high-fat-fed mice developed fatty liver and diabetic symptoms - the same metabolic consequences we see in many over-weight, sedentary people, Shay said.
But the chubby mice that received the extracts accumulated less fat in their livers, and they had lower blood sugar, than those that consumed the high-fat diet alone.
Ellagic acid proved to be a powerhouse in this experiment, too, lowering the high-fat-fed mice's blood sugar to nearly the levels of the lean, normally-fed mice.
The study appeared in The Journal of Nutritional Biochemistry.