From the Guidelines
The Body Mass Index (BMI) for children is determined by age- and sex-specific percentile curves, with a BMI at or above the 95th percentile considered obese and a BMI between the 85th and 94th percentiles considered overweight.
Calculation of BMI
- BMI can be calculated using the formulas: BMI = weight (kg)/(height) (m2) or BMI = weight (lb)/height (in)/height (in) × 703 1
Classification of BMI in Children
- According to the American Heart Association, a BMI between the 5th and 85th percentiles is considered healthy, between the 85th and 95th percentiles is considered overweight, and at or above the 95th percentile is considered obese 1
Key Points
- The Centers for Disease Control and Prevention (CDC) 2000 growth charts are the preferred reference for identifying overweight and obesity in children in the United States 1
- The BMI percentile curves are used to assess weight-for-height relationships in children, as they correlate strongly with direct measures of body fat and identify those with the highest body fat correctly with acceptable accuracy 1
- Clinicians are encouraged to use the age- and sex-specific BMI standards for the US population, published as percentile growth curves by the CDC, to replace older weight-for-height curves 1
- The 95th percentile is likely to correspond to 130% of the ideal weight percentile, which corresponds to the child’s age- and sex-specific height percentile 1
- Children and adolescents with a BMI greater than the 95th percentile should undergo additional evaluation for obesity-related complications, such as blood pressure measurement, lipoprotein analysis, and fasting insulin and glucose determination 1
From the Research
Definition of Body Mass Index (BMI) for Children
- BMI is a measure of weight adjusted for height, calculated as weight/height(2) 2
- It is a simple and noninvasive surrogate measure of body fat, but has limitations in differentiating body fat from lean mass 2, 3
Use of BMI in Children
- BMI has been recommended for evaluating overweight and obesity in children and adolescents in the clinical setting 3
- It is an inexpensive and easily implemented tool that can provide insight for clinicians, patients, and caregivers 4
- BMI percentiles are used to define overweight and obesity, but may not adequately define risk of comorbid conditions 3
Limitations of BMI in Children
- BMI has low-moderate sensitivity and may not accurately differentiate between fat and fat-free mass 2
- It may not be optimal for stratifying children and adolescents with very high BMI 3
- BMI percentiles may not correctly classify body fatness in all children, particularly those with a BMI between the 85th and 94th percentiles 5