Body mass index (BMI) has been the dominant method for classifying obesity for more than half a century. It is an easy calculation, simple to deploy at scale (pun intended), based on one's weight and height - BMI = (weight in kg) / height in meters)2) making it useful for population-level surveillance. However, as researchers have repeatedly pointed out, it was never designed to assess health risk in individuals—a distinction that matters in clinical care, employment screening, and fitness-for-duty decisions.
Among the most prominent voices highlighting this gap is Dr Margaret Ashwell OBE, former president of the UK Association for Nutrition, whose work has consistently shown that where fat is stored may matter more for health risk than total body weight alone.
BMI and mortality don’t align as well as we thought
In a 2014 analysis, Ashwell and colleagues revisited data from the UK Health and Lifestyle Survey, a cohort originally recruited in the mid-1980s, similar to the US NHANES annual surveys. Using records with approximately 20 years of follow-up, they showed that the waist-to-height ratio (WHtR) was more strongly associated with mortality risk and years of life lost than BMI.
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