Researchers examine relationship between childhood obesity, physical activity

American College of Sports MedicineDec 7 2010

ACSM journal article probes relationship between childhood obesity, physical activity

Scientists may have discovered a new trend in childhood obesity, according to research published this month in Medicine & Science in Sports & Exercise®, the official journal of the American College of Sports Medicine. In comparing physical activity levels among American children, researchers discovered that the most overweight and obese ethnic groups are also some of the most active. This work adds to a growing understanding of the complex relationships among physical activity, nutrition, weight management, fitness and health.

The study "Physical Activity in U.S. Youth: Effect of Race/Ethnicity, Age, Gender, and Weight Status" reports that of the three ethnic groups compared – Caucasian, black and Mexican American – Caucasian children are overall the least active. Black children, on the other hand, are the most active. This finding is surprising, experts say, because the highest prevalence of obesity occurs in some of the more active groups – black and Mexican American children.

"Contrary to our expectations, higher levels of physical activity were not associated with lower rates of obesity across the race and ethnic groups," said Britni Belcher, M.P.H., the lead author of the study.

The research team, representing the University of Southern California and National Institutes of Health, compared 3,106 American children, looking at age, race/ethnicity, body mass index, physical activity and dietary intake. Accelerometers measured participants' physical activity for four days, providing data on each child's levels of sedentary, moderate, vigorous and moderate-to-vigorous physical activity. Researchers suggest that general predisposition to obesity, socioeconomic status and cultural differences in behavior may play a role in the study's findings.

"This paradox may be accounted for by the fact that non-Hispanic white youth may spend more time in activities not captured well by accelerometry, such as swimming or bicycling," said Donna Spruijt-Metz, Ph.D., associate professor at the University of Southern California's Keck School of Medicine and senior author. "These differences could also be attributed to the higher socioeconomic status found in the non-Hispanic white youth because higher socioeconomic status has been related to lower risk of obesity."

The study also finds that children are less active after they hit puberty, as the 6-11 age group engaged in twice as much physical activity as children in the 12-15 and 16-19 age groups. Additionally, Spruijt-Metz and her colleagues find that males engage in more physical activity than females, irrespective of race or ethnic group. In fact, females of normal weight generally achieved less physical activity than their obese male counterparts.

Data from this study are from the National Health and Nutrition Examination Study, a cross-sectional health interview survey representative of the U.S. civilian, noninstitutionalized population. All analyses were conducted in SAS 9.1 (SAS Institute, Inc.) using specialized procedures.