BMI may not be the right tool to measure health risks

The BMI is easy to measure, cheap to compile and track, and simple to convey to patients, but it was never meant to be a predictor of an individual's health risks. It was intended as a useful metric to track changes in the health and nutrition of large populations. For patients who are very muscular, and for African Americans, BMI is often a poor gauge of body composition. For Asians and people who are sedentary but slim, a reliance on BMI can lead a physician to overlook signs of elevated disease risk. A child's BMI, which is calculated differently than that of an adult, is also an imperfect predictor of illness or early death.

The BMI continues to dominate research on obesity and guide physicians' advice to patients. But some researchers have launched a rear-guard effort to knock the measure from its place atop the public-health pedestal. To replace — or at least supplement — the BMI, they are searching for measures that might offer individual patients a better gauge of their health risks, as well as a wider range of options to better their odds of staying healthy.

They'll also need tools to do so that are as cheap and simple as the BMI. Most techniques that measure body composition, including the Bod-Pod, the dual-energy X-ray absorption test (DEXA), and hydrostatic underwater weigh-in, are costly and time-consuming. Bioelectrical Impedance Analysis, an inexpensive and reliable gauge of body composition increasingly used in weight-management programs, may be practical in some general medical practices. But researchers are increasingly looking for ways to capture such information with tools as simple and inexpensive as tape measures.

One of the easiest alternatives to the BMI is waist measurement. With growing evidence that fat girdling the waist and visceral organs disturbs metabolism, the circumference of a patient's midsection has been shown to be a better predictor of Type 2 diabetes risk than the BMI.

Finally, an increasing number of researchers cite a major gap in the BMI: its inability to reflect the health effects of an individual's exercise habits. At least seven high-profile studies in the last decade have established that even for people with high BMIs, cardiovascular risk and the likelihood of early death are driven down significantly by maintaining a high level of fitness or at least regular physical activity. The risk of Type 2 diabetes also falls, although in that case, studies suggest that whittling waist circumference is a better strategy still.

Source: L.A. Times