Involvement in sports, for example, was tied to a lower risk of obesity in boys but not girls and drinking milk was linked to lowered risk among girls but not boys, according to researchers from the University of Michigan Health System in Ann Arbor.
The study's authors, led by Dr. Elizabeth Jackson, write in the journal Pediatrics that understanding obesity risk factors for specific genders may help target programs aimed at weight loss or preventing weight gain in children.
The U.S. Centers for Disease Control and Prevention estimates that about 17 percent of children and teens are obese.
For the new study, Jackson and her colleagues used data collected between 2004 and 2011 from 1,714 sixth-grade students at 20 middle schools in and around Ann Arbor.
Overall, about 18 percent of boys and 16 percent of girls were obese, which is defined as children who are in the top-fifth percentile of body mass index - a measurement of weight in relation to height.
Among boys who were not obese, about 56 percent participated in at least 20 minutes of vigorous physical activity at least five times per week, compared to about 43 percent of boys who were obese.
But there was no difference between the percentage of obese and non-obese girls who reported regular vigorous physical activity.
Playing on at least one sports team was also linked to decreased risk of obesity for boys but not girls.
The lack of an association between obesity and physical activity in girls may be explained by girls not reporting some activities like cheerleading or dance, because children may not consider those activities sports, the researchers write.
They did find, however, that drinking two or more servings of milk per day was tied to about a 20 percent decreased risk of obesity among girls but not boys. One possible explanation is that milk is displacing sugary drinks in the girls' diets, Jackson's team writes.
Image: Overweight girl, via Shutterstock