How are Overweight and Obesity Defined?

There are several methods to measure obesity levels including Bioelectrical Impedance Analysis, Hydrostatic (underwater) Weighing and Dual Energy X-ray Absorptiometry.

Bioelectrical Impedance Analysis is typically the most practical and convenient method used by bariatricians. The Body Mass Index (BMI) is a screening tool to identify people who may be at increased health risk due to being overweight or obese. The BMI formula = weight in pounds / (height in inches x height in inches) x 703. The following classifications for BMI were recommended by the National Heart Lung and Blood Institute:

Underweight: lower than 18.5
Normal weight: 18.5 to 24.9
Overweight: 25 to 29.9
Obesity: 30 to 34.9 (Class 1)
Obesity: 35 to 39.9 (Class 2)
Extreme Obesity: greater than 40 (Class 3)

Waist-to-hip measurements are also critical. These are obtained by dividing the circumference of an individual’s waist by their hips. A healthy waist-to-hip ratio for women is no more than 0.8 and a healthy ratio for men is no more than 0.95.

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