April 19, 2014

YES, BODY MASS INDEX IS STUPID WHEN USED FOR INDIVIDUALS: A Number That May Not Add Up.

The index was devised in the 1830s from measurements in men by a Belgian statistician interested in human growth. More than a century later, it was adopted by insurers and some researchers studying the distribution of obesity in the general population. Though never meant to be an individual assessment, only a way to talk about weight in large populations, B.M.I. gradually was adopted as an easy and inexpensive way for doctors to assess weight in their patients.

At best, though, B.M.I. is a crude measure that “actually misses more than half of people with excess body fat,” Geoffrey Kabat, an epidemiologist at the Albert Einstein College of Medicine, has noted. Someone with a “normal” B.M.I. can still be overly fat internally and prone to obesity-related ills.

Calling B.M.I. an imperfect predictor of a person’s health risks, the Centers for Disease Control and Prevention cautions doctors against using it as a diagnostic tool.

For one thing, body weight is made up of muscle, bone and water, as well as body fat. B.M.I. alone is at best an imprecise measure of how fat a person may be. When Arnold Schwarzenegger was Mr. Universe, his B.M.I. was well in the obese range, yet he was hardly fat.

Another problem: the distribution of excess body fat makes a big difference to health. Those with lots of abdominal fat, which is metabolically active, are prone to developing insulin resistance, elevated blood lipids, high blood pressure, diabetes, premature cardiovascular disease, and an increased risk of erectile dysfunction and Alzheimer’s disease.

But fat carried in the hips, buttocks or thighs is relatively inert; while it may be cosmetically undesirable, it is not linked to chronic disease or early death.

An easy-to-get number that’s bogus will nonetheless be widely used, because it’s an easy-to-get number.