Scientists are using imaging tests to show for the first time that fructose can trigger brain changes that may lead to overeating.
Fructose is a sugar that saturates the American diet.
Researchers have found that after drinking a fructose beverage, the brain doesn't register the feeling of being full as it does when simple glucose is consumed.
It's a small study and does not prove that fructose or its relative, high-fructose corn syrup, can cause obesity, but experts say it adds evidence they may play a role.
These sugars often are added to processed foods and beverages, and consumption has risen dramatically since the 1970s along with obesity. A third of U.S. children and teens and more than two-thirds of adults are obese or overweight.
For the study, scientists used magnetic resonance imaging, or MRI, scans to track blood flow in the brain in 20 young, normal-weight people before and after they had drinks containing glucose or fructose in two sessions several weeks apart.
One study leader says that scans showed that drinking glucose turns off or suppresses the activity of areas of the brain that are critical for reward and desire for food.
Yale University endocrinologist Dr. Robert Sherwin adds that with fructose, "we don't see those changes" and as a result, "the desire to eat continues -- it isn't turned off."