Scientists at Washington State University have shown that berries, grapes and other fruits can convert excess white fat into calorie-burning ‘beige’ fat.

In the study, recently published in the International Journal of Obesity, mice were fed a high-fat diet, but those that also consumed resveratrol, the antioxidant found in fruits, gained about 40 per cent less weight. The mice needed the equivalent of just 12 ounces of fruit a day for humans to see the effect.

The positive effects of resveratrol have been widely publicised, but scientists had been unclear about how it helped to fight obesity.

"Polyphenols in fruit, including resveratrol, increase gene expression that enhances the oxidation of dietary fats so the body won't be overloaded," said professor of animal sciences Min Du. "They convert white fat into beige fat which burns lipids off as heat – helping to keep the body in balance and prevent obesity and metabolic dysfunction."

Du said resveratrol is only one of the polyphenolic compounds found in fruit that provides beneficial health effects.

“We think you can increase your total intake of polyphenol compounds by directly increasing fruit consumption,” said Du. He said while the compounds are found in all fruits, they are especially rich in blueberries, strawberries, raspberries, grapes and apples.