Obese children tend to have an exceptionally responsive sweet tooth—and it shows up as a visible signal in their brains.

That’s according to a small yet intriguing study led by researchers at the medical school of UC San Diego, who published their results Dec. 11 online in the International Journal of Obesity.

In the study, 13 children of healthy weight and 10 obese peers, all between 8 and 12 years old and none feeling hungry, underwent functional MRI while swirling sugared water and focusing on the taste with eyes shut.

In the obese group, the insular cortexes and amygdala—regions of the brain associated with emotion, motivation and reward—lit up with heightened activity in the fMRI images.

The study authors stated in a news release that the work doesn’t show a causal relationship between sugar hypersensitivity and overeating, but it does lend credence to the theory that America’s obese and overweight youth—who now number close to 1 in 3—get a higher-than-normal lift from sugary foods and drinks.

“The take-home message is that obese children, compared to healthy weight children, have enhanced responses in their brain to sugar,” said lead author Kerri Boutelle, PhD, a clinical psychologist, UC psychiatry professor and founder of the university’s Center for Health Eating and Activity Research (CHEAR).

The obese children did not show any heightened neuronal activity in a third area of the brain, the striatum, that is also part of the response-reward circuitry, according to the release. Other studies have shown this area to be associated with obesity in adults.

UC San Diego pointed to previous studies showing that children who are obese have an 80% to 90% chance of growing up to become obese adults.

“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,” said Boutelle. “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.”

The website of NIH’s Heart, Lung and Blood Institute lists a dozen or so health risks associated with obesity.

To access the study, Increased brain response to appetitive tastes in the insula and amygdala in obese compared to healthy weight children when sated, click here (subscription or payment required).