What is a healthy weight? A definitive answer to this seemingly innocent question continues to evade the medical community. In 1832, Belgian statistician Adolphe Quetelet introduced the concept of body mass index (BMI) — one's weight (in kilograms) divided by the square of one's height (in meters) as a measurement of ideal body weight. Approximately 140 years later, nutritional epidemiologist Ancel Keys proposed the use of BMI as a surrogate marker for evaluating body fat percentage within a population.
For the past 50 years, the scientific and medical communities have relied on BMI as a research and study tool to categorize patients' weight (ie, severely underweight, underweight, normal weight, overweight, and obesity). The World Health Organization, National Institutes of Health, and US Centers for Disease Control and Prevention use the following BMI weight classifications for adult patients:
Underweight: BMI < 18.5
Normal weight: BMI ≥ 18.5 to 24.9
Overweight: BMI ≥ 25 to 29.9
Obesity: BMI ≥ 30
Of note, BMI categories for children and adolescents (aged 2-19 years) are based on sex- and age-specific percentiles and will not be addressed in this article.
BMI appears to be a straightforward, easy, and cost-effective way to identify "healthy" weight and assess a patient's risk for
