December 11, 2008

Obesity Gene Causes Fast Food Cravings

Genes that have been linked to increased risk of obesity might be the reason some people choose french fries over apples, according to scientists.

A study found that children with a common variation of the gene tend to overeat high-calorie foods. They ate 100 extra calories per meal, which puts on more weight long term, said Colin Palmer, who led the study at the University of Dundee in Scotland.

He said that the findings do not mean that everyone with that version of the gene will eat too much and become obese. 

"It's still your choice," he said. "This gene will not make you overweight if you do not overeat."

The results support the theory that childhood obesity today could be connected with widespread availability and low cost of high-calorie foods. 

Scientists discovered last year that the gene, named FTO, was linked to obesity but they did not know why.  Most of the other genes were thought to affect the body weight and influence appetite.

The scientists wanted to know if the FTO gene also had to do with eating behavior, or whether it helps the body burn calories.  Over 2,700 Scottish children ages 4 to 10 were studied through extensive tests.

Close to two-thirds of the children had one copy of the gene variant, about the same proportion found in last year's study of mostly white Europeans.  One copy of the gene variant had 30 percent increased risk of obesity. 

The variation of the gene is found in other populations; the frequency in Chinese is about half that of Europeans.

After confirming the obesity link in the larger Scottish group, researchers examined 97 of the children.  Measurements were taken, including body fat and metabolic rate.

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

The 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.

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

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

The overheating may be driven more by the need for calories than a preference for fatty foods, according to Leibel.

"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 New England Journal of Medicine.

According to a recent study, the Amish suggest the variant's effect could be blunted with hours of physical activities.  The lead author of the study, Evadnie Rampersaud of the University of Miami, noted that 76 Scottish children completed all three meals.

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

The Scottish researcher, Palmer, said there is no political reason to screen people for the gene variation, because there's more likely to be many genes that affect obesity.

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

Last year's study, Palmer's DNA was included but he did not know his status, though he does have a weakness for potato chips.


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