Lack of physical activity is the main contributor to obesity in 11- to 15-year-olds, according to a study by University of California San Diego School of Medicine and San Diego State University researchers released Monday. The study, published in this month's Archives of Pediatric and Adolescent Medicine, looked at 878 adolescents from the practices of 45 primary care physicians in six San Diego County clinics. "Insufficient physical activity and too much time spent on sedentary behaviors like computer games and watching TV may equal, and even exceed, diet quality as important contributors to (being) overweight in adolescence," wrote Kevin Patrick, a UCSD professor and the study's principal investigator. According to the study, 45.7 percent of the 878 children were either at risk for becoming overweight, or were already classified as overweight by the standard body mass index for age. The researchers compiled data on minutes of physical activity per day, hours of television per day, percentage of calories from total fat, percentage of calories from saturated fat and amount of fiber consumed per day. According to the researchers, weight in boys was related to the amount of time spent watching television. Boys who were overweight or at-risk of becoming overweight reported significantly more minutes of television watching during a nonschool day, an average of 141.5 minutes, than the normal weight boys, who reported an average of 108.4 minutes per day. There was no correlation between television watching and weight found in girls, according to the study. "There's often too much emphasis on what people consume and not on how much energy they're expending during a given day," Patrick said. The researchers also found that fiber intake, and not fat calories, was mostly closely related to an individual's weight. Normal weight children in the study consistently reported higher intakes of fibrous foods such as whole grains, fruits and vegetables, compared to the at-risk and overweight children. According to the study, the percentage of calories consumed from fat did not differ significantly between the normal weight children and those identified as being at risk for obesity, or those who were already overweight. Researchers also found that 54.8 percent of Hispanic girls were either overweight or at risk for obesity, compared to 42 percent of non-Hispanic girls. However, no difference was found for the weight status between boys based on their ethnic heritage. The study was funded by the National Cancer Institute.