• Rachael W Taylor, Ianthe E Jones, Sheila M Williams, and Ailsa Goulding.
• Departments of Human Nutrition, University of Otago, Dunedin, New Zealand. rachael.taylor@stonebow.otago.ac.nz
• Am. J. Clin. Nutr. 2002 Dec 1;76(6):1416-21.

BackgroundBody mass index (BMI; in kg/m2) cutoffs for use with children and adolescents aged 2-18 y that correspond to the well-accepted BMI cutoffs for overweight (> or = 25 but < 30) and obesity (> or = 30) in adults were published recently.ObjectiveThe objective was to estimate the percentage body fat (%BF) values typically associated with these BMI cutoffs in children and adolescents.DesignThe %BF was measured by dual-energy X-ray absorptiometry in 661 subjects (49% male) aged 3-18 y. Regression equations using BMI, age, and sex were developed to predict the %BF associated with BMI cutoffs for overweight (age-specific BMI equivalent to a BMI of 25 in an 18-y-old) and obesity (age-specific BMI equivalent to a BMI of 30 in an 18-y-old) over this age range.ResultsMeasurements classified 17.1% of males and 19.8% of females as overweight and 5.5% of males and 7.5% of females as obese. The %BF associated with an obese BMI tended to be higher in peripubertal males (34-36%) than in younger (24-30%) or older (27-30%) males. Although the predicted %BF of young females was similar to that of young males, values rose steadily with age, such that an 18-y-old female with a BMI of 30 had an estimated %BF of 42%, whereas that in males of similar age was 27%.ConclusionThe %BF values associated with BMI classifications of overweight and obesity vary considerably with age in growing children, particularly in girls.

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