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A study of a large, multiethnic sample found that shifts in body mass index (BMI) are common in middle-school students. Are these changes associated with meaningful changes in cardiometabolic risk factors?
A total of 3,993 children participating in the HEALTHY study, a multisite, school-based study designed to mitigate risk for type 2 diabetes mellitus, underwent health screenings at the beginning of the sixth grade and end of the eighth grade. The average age of the students at baseline was 11.3 years; 48% were boys, 60% were Hispanic, and 50% were overweight or obese.
Over the 2.5 years of the study, the researchers noted a “striking amount” of shifting across BMI categories. Most children who were in the healthy-weight range in sixth grade remained there at the end of eighth grade, but 13% became overweight. Among those who were overweight at baseline, 36% moved to the healthy range, 51% remained overweight, and 13% became obese or severely obese. Among children who were obese at baseline, 32% improved BMI category, but 62% remained obese, and 6% became severely obese. BMI shifts were not explained by differential increases in height across categories and were not associated with school intervention programs or other variables.
Increases in BMI were associated with worsening of cardiometabolic risk factors, including blood pressure, lipids, and waist circumference, whereas decreases were associated with improvements.
The findings provide compelling evidence of the need for obesity-prevention efforts for middle-school students across all BMI categories to promote decreases in BMI for children who are overweight and obese and to prevent increases in those in the healthy range, the researchers conclude.