More doubts about accuracy of BMI

Obesity has long been tied to critical health issues, including Type 2 diabetes, heart disease and some forms of cancer. In fact, one recent study links long-term obesity in young people to heart disease in middle age.

Your body mass index (BMI) is calculated using weight and height to approximate a measure of healthy body weight. For example, a 6-foot, 200 lb. person would have a BMI of 27.2. Any measure over 24.9 is considered overweight, while over 30 indicates obesity.

Now, however, scientists at the University of Pennsylvania have called into question the BMI, the standard for healthy weight measurement since it was developed in 1892. In an editorial in the journal Science, Dr. Rexford Ahmia and Dr. Mitchell Lazar write that, though most studies depend on BMI as a measure of healthy weight, it may not be an accurate measure. The researchers indicate that BMI doesn’t account for the reasons a person may be carrying excess weight, including genetic, behavioral, psychological and social factors.

In addition, they say BMI isn’t an indicator of metabolic health, the rate at which your body metabolizes the foods you eat and nourishes your cells, or muscle mass.

“There is an urgent need for accurate, practical and affordable tools to measure fat and skeletal muscle, and biomarkers that can better predict the risks of diseases and mortality,” said Dr. Ahima in a statment. “Advances to improve the measurement of obesity and related factors will help determine the optimal weight for an individual, taking into account factors such as age, sex, genetics, fitness, pre-existing diseases, as well novel blood markers and metabolic parameters altered by obesity.”

The debate on the value of BMI is nothing new to the medical community, says Dr. Paul Ringel, physician at Advocate Illinois Masonic Medical Center in Chicago.

“Your BMI is a measure of healthy weight,” Dr. Ringel says. “If high, it may predispose you to serious health issues.”

An alumnus of the University of Pennsylvania, Dr. Ringel says he somewhat disagrees with his fellow Quakers.

“It’s true that BMI is a non-specific assessment of abnormal weight,” he says. “But, it’s also true that how that weight is distributed is of more concern.”

Given two obese patients, one with an “apple shape”—a large belly—and one with a “pear shape”—large hips—it’s very clear that the person with more abdominal fat is at a greater risk for health conditions such as Type 2 diabetes and cardiovascular diseases, he says.

“BMI is an imperfect tool; however, from a public health point of view, it’s a good screening measure to help identify those who are at greater risk and need more attention.”