A new study shows girls who became overweight between the time they started kindergarten and finished the third grade suffered a decline in test scores and social skills and scored lower than girls who were not overweight.
But boys who gained weight in their early school years suffered far fewer negative consequences.
Researchers say the study adds to previous research that being overweight has a particularly negative effect on girls' academic performance and social development.
Weight Affects School Performance
In the study, researchers analyzed a national sample of 7,000 children in the U.S. who entered kindergarten in the 1998-1999 school year and were followed though the end of the third grade. Information on the children's body mass index (BMI, a measure of weight in relation to height used to indicate overweight and obesity) was collected at the beginning and end of the study as well as information on their school performance.
The results showed that 9 percent of the children were overweight when they entered kindergarten and remained overweight through the third grade. Another 8 percent who were not overweight when they started kindergarten had become overweight by the end of third grade.
Researchers found reading and math tests scores were significantly higher among normal-weight children compared with those who were overweight from the beginning and those who became overweight during their first years at school.
But this relationship was much weaker among boys than among girls.
Overweight Girls Particularly Vulnerable
"We find that girls who became overweight between kindergarten entry and end of third grade were significantly more likely to score lower on math and reading tests, score higher on teacher-reported externalizing behavior problems, and score lower on teacher ratings of self-control, interpersonal skills, and approaches to learning compare with girls who were never overweight," writes researcher Ashlesha Datar, Ph.D., and colleagues at the RAND Corporation.
"Interestingly, girls who were always overweight were not significantly different on most outcomes compared to girls who were never overweight, with the exception of internalizing behavior problems."
In contrast, there were no significant differences in test scores, internalizing behavior problems, and ratings of self-control among overweight and normal-weight boys. But boys who became overweight had a higher rate of absences in third grade than boys who were never overweight.
Although the relationship between being overweight or becoming overweight was largely associated with negative outcomes among schoolchildren, researchers did find one positive relationship.
Boys who started school overweight or became overweight by the third grade had fewer teacher-reported externalizing behavior problems, like bullying, than boys who remained normal weight.
SOURCE: Datar, A. International Journal of Obesity, Sept. 1, 2006; vol 30: pp 1449-1460.
By Jennifer Warner
Reviewed by Louise Chang