Body weight alone is not an accurate measure of healthy weight. This is because it doesn't take into account how tall a person is. Body mass index, or BMI, uses an equation taking both height and weight into account. Despite some issues, it is among the most widely accepted gauges of obesity.
BMI Basics
The body mass index derives from an equation that accounts for both height and body weight. Developed in Europe, the original BMI equation is simple: weight in kilograms divided by height in meters squared. The United States uses a slightly more complex conversion: weight in pounds times 703, divided by height in inches squared. In both cases, a result between 18.5 and 24.9 indicates healthy body weight. Scores above that indicate an overweight person, with scores below indicating somebody unhealthily underweight.
Invention
The BMI was originally named the Quetelet Index of Obesity after its inventor, Beldian statistician Adolphe Quetelet. Although Quetelet developed his index in the late 19th century, the practice of using height-for-weight tables continued as the most common practice until the late 20th century. In 1972, the "Journal of Chronic Diseases" ran a story coining the phrase "body mass index" and initiated its rise to more common usage.
Acceptance and Variations
By the 1980s, the BMI had been adopted my the World Health Organization and many national governments as their official gauge of healthy weight and obesity. All countries use Quetelet's basic formula, although some adhere to a different scale. Both Japan and Singapore, for example, skew their scales to place the range of "normal" weight lower than that of the standard scale. Some U.S. authorities have proposed the exact opposite, shifting the range to permit higher weights to be counted as healthy.
Weaknesses and Alternatives
The major complaint leveled against using the BMI is that it doesn't take into account different body composition. Muscle is denser than fat -- so much so that many Olympic and professional athletes rate as overweight or even obese on the BMI scale. The most commonly used alternative to the BMI is body fat percentage, which rates body weight according to how much is composed of fat versus lean tissue.
References
- "Eat, Drink and Be Healthy"; Dr. Walter Willett, et al.; 2006
- MayoClinic.com: BMI
- What Health: BMI
- "You: The Owner's Manual"; Dr. Mehmet Oz; 2006
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