The surprising finding, published in the journal Community Dentistry and Oral Epidemiology, comes from researchers at the Eastman Dental Center at the University of Rochester Medical Center. They analyzed data from nearly 18,000 children who participated in two separate major surveys that were part of the large and ongoing National Health and Nutrition Examination Survey.

Among youngsters ages 2 to 5, there were no differences in rates of tooth decay. However, among children ages 6 to 18, those who were overweight or at risk for becoming overweight had fewer cavities than kids of normal weight. A child was considered overweight if he or she was in the 95th percentile or higher, based on age and sex. Children in the 85th percentile or above were defined as at risk for becoming overweight.

The findings don't mean being overweight protects teeth, but they do raise questions about the differences in foods eaten by overweight children compared to their normal weight peers. It also debunks the stereotype of the overweight child who binges on cavity-causing candy and sugary foods. One theory is that overweight children may actually be eating fewer cavity-causing sweets than normal weight kids and instead overeating fatty foods.

"We expected to find more oral disease in overweight children of all ages, given the similar causal factors that are generally associated with obesity and caries," said Eastman Dental Center's Dr. Dorota Kopycka-Kedzierawski, the lead author. "Our findings raise more questions than answers. Research to analyze both diet and lifestyle is needed to better understand the results."