Researchers studied the genotypes of almost 500 black and white American children, aged 5 to 25, and found those from lower socioeconomic backgrounds were more likely to display the negative effects of genes that are known to be involved in causing obesity.

The findings were to be presented this week at the American Physiological Society conference in Augusta, Ga.

"Some gene effects were dependent on socioeconomic status. If you are a carrier of the 'bad gene,' so to say, and you are also in a lower socioeconomic class, then you will show the effect of the gene and are obese," researcher and genetic epidemiologist Dr. Harold Snieder says in a news release.

"If you are in the middle or higher socioeconomic class, you don't show any effects of the gene. So that means only in a bad environment do the effects of these genes come out," Snieder says.

"We don't know which part of the socioeconomic status is responsible for children being obese, but physical activity and diet are likely to play a role," he adds.