Sacramento Bee illustration

Sacramento Bee illustration

As if the nation's weight problems were not daunting enough, a new study has found that the body-mass index, the 200-year-old formula used to distinguish between healthy and unhealthy weight, may be misclassifying roughly half of women and just over 20 percent of men as healthy when their body-fat composition suggests they are obese.

The study, published in the journal PLoS One, uses a patient's ratio of fat-to-lean muscle mass as the "gold standard" for detecting obesity and suggests that it may be a bellwether of an individual's risk for health problems.

The study finds that for women over 50 especially, many whose BMIs suggest they are the picture of health are, in fact, dangerously fat. The measure in the study uses a costly diagnostic test called dual-energy X-ray absorptiometry, or DEXA, which already is in wide use as a means of evaluating bone density.

The new research also suggests that BMI is a poor measure of fatness in men, but not always in a way that underestimates their obesity. Far more frequently than for women, men who were obese by the BMI standard were re-categorized as normal and healthy when the DEXA standard was used.

"We may be much further behind than we thought" in addressing the nation's crisis of obesity, say the co-authors, New York physician Eric Braverman and New York City Commissioner of Public Health Nirav R. Shah.

Braverman derided BMI as "the baloney-mass index," and said that its widespread use "is feeding the failure" of measures aimed at fighting obesity. Efforts to get patients to lose weight have produced short-term weight loss and often, as weight is regained, fatter patients, said Braverman. If medical interventions sought to shift patients' body composition more toward lean muscle mass, he said — encouraging more exercise and more sleep as well as more healthful eating — they would be more successful.

The article comes as the nation's obesity experts are casting about for better ways to measure the nation's state of health and to judge the success or failure of treatment programs. In the past year alone, researchers have proposed a wide range of alternatives to the BMI, and increasingly used them to measure the effectiveness of interventions such as weight-loss counseling, exercise regimens and drug therapies. Simple measures such as waist circumference, hip circumference and waist-to-hip ratios have gained new adherents as criticism of BMI has mounted.


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