The research: Hoping to learn more about the ties between BMI and mortality, the study team examined the health data of more than 246,000 people. At first, their findings supported the older research linking “overweight” BMIs in the 25-to-29.99 range to the lowest mortality rates. But after adjusting their findings to exclude people with preexisting illnesses and smokers—two groups that tend to have lower body weights despite their poor health—the study authors found BMIs at the high end of “normal” had lower mortality rates than people in the “overweight” category. What it means: BMI is a simple calculation based on just two factors: your height and your weight, making it a convenient way to categorize large groups of people. But it becomes a much thornier metric when applied to individuals, says Timothy Church, MD, PhD, of Louisiana State University’s Pennington Biomedical Research Center. “BMI only gets at what you weigh, not where you weigh,” Dr. Church explains, adding that fat around your waist is a lot more dangerous than fat elsewhere on your body. He says BMI also doesn’t take into account your fitness activity, your body fat versus muscle, and a hundred other factors that determine your overall health. And the latest research demonstrates how easily the relationship between BMI and mortality rates can shift based on the type of data included (or excluded). The bottom line: BMI can be a helpful measure of general health when examined alongside many other lifestyle and family history factors like your diet and exercise habits, your blood profile, and any diseases that run in your family, Dr. Church says. But you shouldn’t rely on BMI alone to tell you whether you’re healthy. A simpler, more-reliable predictor of health is your waist circumference. “Measure the distance around your waist at the top of your hipbones,” he suggests. An unhealthy measurement would be over 35 inches for women, and over 40 inches for me. “This still leaves a lot out. But it’s a more accurate judge of health than your BMI,” Dr. Church says. More from Prevention: ABSI: A Better Measure Than BMI?
