When it comes to BMI—the most common measure of obesity—the price is right.
BMI, or body-mass index, is calculated by dividing weight in kilograms by height in meters squared. A result less than 18.5 is considered underweight, according to the Centers for Disease Control and Prevention; 18.5 to 24.9 is healthy; 25 to 29.9 is overweight; and 30 or higher is obese.
Medical experts rely on BMI to assess the prevalence of obesity because it’s simple, cheap and generally accurate.
But the index doesn’t distinguish fat from muscle or other tissue, and that causes some people to be placed in the wrong category.
“We have two different groups that tend to be misclassified,” said Luiz Guilherme Grossi Porto, a professor of physical education at Universidade de Brasília and a visiting scientist and collaborator at Harvard University.