Love it or hate it, BMI is back in the news. But that’s just the starting point in a debate over how to define obesity.
Critics have long faulted the weight-divided-by-height-squared measure as too blunt an instrument to define obesity. BMI, or body mass index, alone can group people with excess muscle mass in the same bucket as people with excess fat, all while ignoring population differences. Over a year ago, a Lancet Diabetes and Endocrinology global commission took aim at redefining obesity, relying less on BMI and more on such consensus-gaining metrics as waist circumference, waist-to-hip ratio, or waist-to-height ratio.
What was new in the commission’s framework was drawing a bright line between preclinical and clinical obesity, all with an eye toward sharper diagnosis that starts with BMI and other body fat numbers. Someone with preclinical obesity might have excess body fat and be at risk for — but not yet be diagnosed with — cardiovascular problems, type 2 diabetes, some cancers, or other signs of organ dysfunction. Someone with clinical obesity would have already developed an ongoing illness.
