The brains of obese children are more responsive to sugar, according to a recent study from the University of California in San Diego.

Although their study does not show a causal relationship between sugar hypersensitivity and overeating, their findings suggest that the growing number of America's obese youth may have a heightened psychological reward response to food.

This elevated sense of "food reward" -- which involves being motivated by food and deriving a good feeling from it -- could mean some children have brain circuitries that predispose them to crave more sugar throughout life.

"The take-home message is that obese children, compared to healthy weight children, have enhanced responses in their brain to sugar, "Kerri Boutelle, first author of the study, said in a statement.  "That we can detect these brain differences in children as young as eight years old is the most remarkable and clinically significant part of the study."

For the study, researchers scanned the brains of 23 children,ì ranging in age from 8 to 12 years old, while they tasted one-fifth of a teaspoon of water mixed with table sugar. The children were directed to swirl the sugar-water mix in the mouth with their eyes closed, while focusing on its taste.

Ten of the children were obese and 13 had healthy weights, as classified by their mass indices.

Researchers found that the brain images showed that obese children had heightened activity in the insular cortex and amygdala, regions of the brain involved in perception, emotion, awareness, taste, motivation and reward.

"Any obesity expert will tell you that losing weight is hard and that the battle has to be won on the prevention side," said Boutelle, who is also a clinical psychologist. "The study is a wake-up call that prevention has to start very early because some children may be born with a hypersensitivity to food rewards or they may be able to learn a relationship between food and feeling better faster than other children."

According to previous studies, children who are obese have an 80 to 90 percent chance of growing up to become obese adults. Currently about one in three children in the United States is overweight or obese.

The findings are detailed in the International Journal of Obesity.