The children were given three meals at school to evaluate their eating behavior. The meal included a mix of fruits and vegetables, ham, cheese, potato chips, chocolate candies and bread rolls.

The researchers found that children with the gene variation showed no difference in metabolic rates, levels of physical activity or the amount of food eaten.

"The only thing we could find was the fact that they were eating much richer foods," said Palmer.

On average, those with the gene variant ate 100 calories more than those without it.

Dr. Rudolph Leibel, an obesity researcher at Columbia University in New York, said getting good measurements of how much someone eats is difficult, but the Scottish study did it in a closely controlled manner.

He said the overeating may be driven more by the need for calories than a preference for fatty foods. Fat is just a good way to get those extra calories.

"Bite for bite, there are more calories in a Big Mac than there are in an apple," said Leibel, who wrote an editorial that accompanies the study in the journal.

A recent study in the Amish suggested the variant's effects could be blunted with hours of physical activity. The lead author of that study, Evadnie Rampersaud of the University of Miami, noted that only 76 Scottish children completed all three meal tests.

"While the results are intriguing, larger studies are needed to fully explore this hypothesis," she said in an e-mail.

Palmer, the Scottish researcher, said there's no practical reason to screen people for the gene variation; there's likely to be many genes that affect obesity.

And whether you have it or not, he said, the advice would be the same: Eat healthy and exercise.

Palmer's DNA was included in last year's study but he doesn't know his status — though he does have a weakness for potato chips.

(Agencies via China Daily December 12, 2008)