Vol 49, No 5
The Centers for Disease Control, U.S. Surgeon General and World Health Organization have settled on the body mass index (BMI) as the easiest way to measure obesity. BMI is determined by dividing a person’s weight in kilograms by the square of the person’s height in meters.
BMI ratings range from underweight to morbidly obese. (Click here to see an online BMI calculator.)
An average-size man carrying an extra 30 pounds would probably be considered obese. Morbidly obese people usually weigh at least 100 pounds over their recommended weight. Today one in 50 adults is morbidly obese, up from one in 200 in 1986.
Critics of BMI point out that assessments based on height/weight measures are a primitive method for determining excess body fat. (More accurate measures include caliper tests and underwater weighing.) For example, athletes may have BMIs outside the normal range. Critics also note that the BMI scale used in the United States has shifted downward to conform to the World Health Organization’s criteria, abruptly jumping millions of Americans into the overweight and obese categories.
Even critics concede, though, that for most people, BMI is an accurate indicator at least 90 percent of the time. However, since BMI usually is self-reported, researchers say people often fudge the numbers in their favor, suggesting that the epidemic is even worse than the data indicate.