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Physical activity and weight gain over 20 years.

To the Editor: Dr Hankinson and colleagues reported on the relationship of activity and body mass index (BMI) over 20 years in a large, ethnically diverse cohort of young to middle-aged adults participating in the CARDIA study. Weight gain is a major underlying risk factor for mortality secondary to the development of diabetes, heart disease, and cancer. In their analysis, being in the highest tertile of activity was associated with a reduction in the rate of increase in both BMI and waist circumference. However, individuals in this highest activity tertile still experienced significant increases in both BMI and waist circumference over time. In their study, was there an activity level that was associated with no increase in BMI or waist circumference? If so, that level of activity might actually prevent increases in BMI during the transition from young adulthood to middle age. Did that activity level differ by sex or race? Also, was there an ideal ratio of activity to caloric intake at which the observed increases in BMI were minimized? Such information would be useful in counseling young adults about the level of activity needed to maintain a healthy weight and minimize the risk of obesity-related morbidity and mortality.