"This is a possible behavioral mechanism for understanding how it is that a diet drink or diet foods could make you a little overweight," said Dr. Pierce. Previous studies have suggested a link between diet soda consumption and a higher risk of obesity, diabetes and heart disease.

Researchers trained young rats to associate certain flavors with caloric content. Once trained, the researchers observed the rates given snacks flavored with the low-calorie signal would proceed to eat more food than they needed at regular meals. The effect was seen in lean and genetically obese rats, which suggests diet foods may lead to more serious consequences for children who are already overweight.

"I think what it really says is that the best thing to do with children is to give them nutritious foods," Dr. Pierce said, noting that well-balanced diets should correspond to the child's level of daily activity.