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Obesity is either caused by an increase in energy intake, or reduced energy expenditure, or both. However, it is difficult to state with certainty the cause of obesity.

Sue YS Kimm (University of New Mexico, Albuquerque, USA) and colleagues looked at changes in activity and changes in body mass index (BMI) and body fatness in over 1,100 black and over 1,100 white girls from three US cities. The investigators assessed the girls' BMI and skinfold thickness each year from ages 9 or 10 to 18 or 19 years. The girls were given a questionnaire on physical activity and food intake at years 1, 3, 5 and 7-10 of the study. The researchers found that the girls had a pronounced decline in physical activity while their rate of overweight and obesity doubled without a concomitantly large increase in reported energy intake. The authors state that increasing physical activity equivalent to 2.5 hours of brisk walking per week could potentially prevent weight gain, ranging from 4 to 6kg in white girls and 6 to 9kg in black girls during adolescence.

Dr Kimm concludes: "These results suggest that habitual activity plays an important role in weight gain, with no parallel evidence that energy intake had a similar role In view of the global obesity epidemic, maintenance of modest amounts of activity during adolescence could be a method for primary prevention of obesity development and adult-onset chronic diseases. Since the steep decline in habitual activity occurs during adolescence, programmes to moderate and prevent this decline during the teen years might be useful as part of the armamentarium for battling the current epidemic of obesity."

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Contact: Joe Santangelo
j.santangelo@elsevier.com
1-212-633-3810
Lancet
13-Jul-2005