In the early 19th century, doctors still commonly prescribed bloodletting to treat ailments and disease, and a bag of live caterpillars tied around the neck was considered an effective treatment for whooping cough. Yet despite vast scientific advances in medicine since then, many doctors still use the formula for determining healthy body weight that a Belgian mathematician created in the 1830s. This system, now referred to as the Body Mass Index (BMI), measures body fat based on your height and weight and is recommended by both the Centers for Disease Control and National Institutes of Health – even though according to recent research, BMI is inaccurate and unhelpful in evaluating risk of obesity-related diseases and mortality.
“Someone with muscle mass has a lower risk of disease, even if they're overweight according to their BMI,” says Westbury, N.Y.-based Dr. Andre Giannakopoulos, Diplomate on the American Board of Internal Medicine and the American Board of Obesity Medicine and an obesity specialist at the Center for Medical Weight Loss. “For example, a construction worker who's muscular but not necessarily an athlete might be slightly overweight, but that might nevertheless be a healthy weight for him. It's the amount of fat on the body in terms of percentage that contributes to risk.”
Because it doesn't take muscle mass, body fat composition, bone density and racial and sex differences into account, BMI shouldn't be the main tool to determine whether someone is at risk of more than 50 obesity-related health problems and diseases such as cancer, heart disease, hypertension and sleep apnea, says Rexford S. Ahima, M.D., Ph.D., professor of medicine at the University of Pennsylvania Perelman School of Medicine and co-author of an article regarding the difficulty of treating obesity published in the journal Science.
“Although BMI isn't very accurate, it's simple, cheap and can be used for comparative studies in various populations,” Dr. Ahima says. “Accurate measures for body fat, such us underwater weighing, CT scan, MRI and DEXA, are expensive, cumbersome and not practical for large studies.”
But as a growing body of research links obesity with expensive-to-treat chronic diseases, insurance companies are becoming more apt to cover medical treatment for obesity, Dr. Giannakopoulos says. Which is good news for the more than one-third of Americans who are obese.
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“Treating obesity is much more complex than simply telling people to eat less and exercise more,” says Dr. Giannakopoulos. “People can take in fewer calories than their bodies need yet still not lose weight. Looking at overall blood work, for example, can uncover medical issues that could be making weight loss more difficult. A combination of regular office visits, behavior modification, counseling, nutrition help and supplements all can help reverse the medical complications cause by obesity.”