Definitions and Classifications Obesity: excessive amount of body fat relative to body weight; body mass index (BMI) at least 30.0 kg/m 2 Overweight: BMI between 25 and 29.9 kg/m 2 Underweight: BMI less than 18.5 kg/m 2 To identify children and adolescents who are overweight, the 85th and 95th percentile BMI values are used; cutoffs for age and sex are still under discussion.
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