Derived by a Belgian mathematician and astronomer in the 1800s, the BMI tries to identify individuals who are carrying excess weight for their height. But it’s a crude measure (ratio of the weight in kilograms divided by the square of the height in meters) and is known to label anyone who is tall and muscular as overweight. Worse, recent studies show the BMI mislabels a large proportion of people as healthy when they aren’t and vice versa, and misses one of the most accurate indicators of health yet: how much fat you’re carrying around the middle. A study by UCLA researchers just published in the International Journal of Obesity measured the health of 40,420 US adults (from the 2005–2012 National Health and Nutrition Examination Survey) according to several medical health markers, including blood pressure, triglyceride, cholesterol, glucose, insulin resistance and C-reactive protein data. Astonishingly, it found that 47 percent of people classified as overweight by the BMI and 29 percent of those qualified as obese were actually healthy according to at least five of those six health indicators. Meanwhile, over 30 percent of individuals declared as having normal weight by the BMI were cardiovascularly or metabolically unhealthy.
The nail in the coffin for BMI may have been delivered by a study published in the Annals of Internal Medicine, which has shown that an equally simple but much better indicator of health is the amount of belly fat you carry. The study, by researchers from the Mayo Clinic, University of Ottawa Health Institute and St. Anne’s University Hospital in the Czech Republic found that if you compared two men with a BMI of 22, the one with higher belly fat as measured by his waist to hip ratio (the waist girth divided by the hip girth) had a significantly higher mortality risk, and critically, a higher mortality than participants who were overweight or obese according to BMI only. Women with higher central obesity also had a higher mortality risk than those with similar BMI but little belly fat, according to the study. With the United States Equal Employment Opportunity Commission considering rules allowing employers to penalize employees up to 30 percent of health insurance costs if they fail to meet health criteria, the authors of the UCLA study said: “Policymakers should consider the unintended consequences of relying solely on BMI, and researchers should seek to improve diagnostic tools related to weight and cardio metabolic health.”