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Potatoes known for their carbohydrate content and calories have been shown to aid in the fight against weight gainReuters

Potatoes have turned up as unlikely saviours in the fight against obesity. Potato extract may limit weight gain from a diet that is high in fat and refined carbohydrates, says a study by McGill University scientists.

Mice fed on high fat diet for 10 weeks showed that potato extract when given with food helped cut weight gain by more than half.

"The daily dose of extract comes from 30 potatoes, but of course we don't advise anyone to eat 30 potatoes a day," says Stan Kubow, principal author of the study, "As that would be an enormous number of calories," he adds.

Those that started out weighing on average 25 grams put on about 16 grams. But mice that consumed the same diet with a potato extract gained much less weight; only 7 more grams.

"We were astonished by the results," said professor Luis Agellon, one of the study's authors.

"We thought this can't be right – in fact, we ran the experiment again using a different batch of extract prepared from potatoes grown in another season, just to be certain."

Clinical trials will prove the weight reducing efficacy of potatoes on humans.

Potatoes which are known more for their carbohydrate content are also a source of polyphenols protect cells and body chemicals against damage caused by free radicals. They are also believed to work against cancer by blocking certain enzymes that promote the tumour growth. Teas are a rich source of polyphenols also found in fruits and vegetables.

However, it is not yet clear what component in the potato works in fighting weight gain.

More than 2.1bn people in the world are overweight or obese, with the figure set to rise to include nearly half of the population by 2030. A recent report had shown that the burden of obesity in the UK could beat the total costs of war and terrorism.