About Body Mass Index (BMI) Obesity is commonly assessed by using body mass index (BMI), defined as the weight in kilograms divided by the square of the height in meters (kg/m2). A BMI of greater than 25 kg/m2 is defined as overweight, and a BMI of greater than 30 kg/m2, as obese. These markers provide common benchmarks for assessment, but the risks of disease in all populations can increase progressively from lower BMI levels. Limitations of BMISimple BMI calculations may be misleading. According to the existing definition and calculation of BMI, anyone with a BMI of more than 25 would be classified as overweight, regardless of whether their body is composed of fat or muscle. Athletes, for example, may be considered to be overweight even though they may have very little visceral fat. BMI is an imperfect indicator of risk of disease. People with the same BMI but different amounts of visceral fat face different risks of disease. Furthermore, weight is only one among many risk factors. BMI is calculated in the same way for adults and for children, but is interpreted differently for children. The Centers for Disease Control and Prevention (CDC) notes that "for children ages 2 - 20 years, BMI is plotted on a growth chart specific for age and gender." Although some authors use categories such as "moderately overweight" for those with BMI of 25 to 30, the National Heart, Lung and Blood Institute (NHLBI) does not designate overweight with such qualifiers. The extreme obesity classification (BMI > 40) is a commonly used cut-off for determining qualification for bariatric surgery. However, BMI cut-off points for obesity vary around the world. Learn More |
