Two century old formula, Body-mass index BMI, extensively used by medical experts, health insurers and the fitness industry, perhaps classifying nearly half of women and just over 20 per cent of men as healthy when their body-fat composition indicates they are obese, discovers a US new study.
The study uses a patient's ratio of fat to lean muscle mass as the "gold standard" for detecting obesity and suggests that it could be a better bellwether of an individual's risk for health problems.
The researchers suggested that body fat would predict individuals' health risks better than the BMI, the LA Times reported.
To measure fatness, they used a costly diagnostic test called dual-energy X-ray absorptiometry, or DXA, and calculated subjects' level of obesity based on fat-composition standards used by the American Society of Bariatric Physicians.
The results also suggest that the BMI is a poor measure of fatness in men - but not always in a way that underestimates their obesity. In all, 20 percent of the study's men shifted from normal and healthy into the obese column under the new measure.
But far more frequently than was the case among women, men who were obese by the BMI standard were reclassified as normal and healthy when they were measured with the DXA.
Though men fared better than women under the proposed new standard, the resulting picture is uniformly grim, according to the study's authors, Dr. Nirav R. Shah, New York's state commissioner of health, and Dr. Eric Braverman, a New York City internist in private practice.
"We may be much further behind than we thought" in addressing the nation's crisis of obesity, the researchers wrote.
In an interview, Braverman derided the BMI as "the baloney mass index" and said that its widespread use was "feeding the failure" of public health policies and treatments aimed at fighting obesity. The 1,393 patients in the study were from his Manhattan practice.
Efforts to get patients to shed extra pounds have produced weight loss in the short term but fatter patients in the long run as weight is regained, Braverman said.
Medical interventions would be more successful if, instead of focusing on weight, they encouraged patients to shift their body composition toward lean muscle mass by recommending more exercise, more sleep and more healthful eating, he said.
The study was published Monday in the journal PLoS One.