Overweight children have so many burdens to bear -- joint disorders, breathing constriction, emotional difficulties, even more earaches.Now, new research confirms a new woe for the young and overweight: impaired academic performance and basic cognitive function.

University of South Carolina researchers compared the Body Mass Index of over 2,500 kids, ages 8-16, with various measures of mental ability, including memorization and "building block tests" in which children use blocks to reproduce pictures of arrangements.Even after adjusting for confounding factors, such as physical activity levels and television viewing time, overweight children were nearly three times more likely to score poorly on tests measuring visual-spatial organization.

Why may this be? Previous research linking adult obesity with memory, reasoning and attention deficits have promoted the idea that the less brainy may opt for more fattening lifestyles (more TV, less exercise).But this study flips that equation, suggesting that excess weight -- in and of itself -- limits cognitive scope.Abnormally elevated BMIs may harm developing brains, either via oxygen deprivation caused by sleep apnea or irregular insulin activity.Other studies have shown absenteeism rises with childhood BMI.

Fortunately, childhood is prime time for preventing a lifetime of obesity -- and adopting healthy habits have the added bonus of a better report card! Research links improved physical fitness with higher scores on state achievement tests.Children with the highest fruit and vegetable intake are 60% more likely to pass literacy tests while increased consumption of omega-3 sources (like fish and walnuts) may boost IQ.