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Higher Levels of Physical Activity Not Linked to Lower Obesity Rates Across Race and Ethnic Groups

General predisposition to obesity, socioeconomic status and cultural differences likely play obesity role

Conventional wisdom suggests that the less children exercise the more at risk they are at risk of obesity, but a new study finds that the most overweight and obese children are actually members of ethnic groups that are some of the most active.

The research, which suggests a more complex relationship among such factors as physical activity, nutrition, weight management, fitness and health than previously believed, is published the December 2010 journal Medicine & Science in Sports & Exercise.

The study 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.

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."

Other findings

  • 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.
  • Males engage in more physical activity than females, irrespective of race or ethnic group.
  • Females of normal weight generally achieved less physical activity than their obese male counterparts.

Risks of childhood obesity

Nearly one out of three (31.9%) of US youth are either obese or overweight as measured by body mass index (BMI).  Elevated BMI is related to an increased risk of type 2 diabetes, elevated cholesterol, and high blood pressure in youth.  Coupled with the fact that obesity has been shown to track into adulthood, these findings place overweight and obese youth at a significant health risk asthey progress into adulthood.

Study background

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.

Data from this study were from the National Health and Nutrition Examination Study, a cross-sectional health interview survey representative of the U.S. civilian, noninstitutionalized population.

Source: American College of Sports Medicine; Belcher B, Berrigan D, Dodd K, Emken B, Chou C-P, Spruijt-Metz D. "Physical Activity in U.S. Youth: Effect of Race/Ethnicity, Age, Gender, and Weight Status"  Medicine & Science in Sports & Exercise (2010) 42 (12): 2211-2221.  

Posted December 8, 2010