Study finds BMI alone can misclassify obesity

An international study published in Nature found that combining body mass index (BMI) with waist measurements and assessments of organ function can distinguish excess body fat from obesity that is already impairing health. The findings, based on data from 844,108 adults in China, the United Kingdom, the United States and Spain, show how BMI alone can both miss excess adiposity and classify some people as obese when waist measures do not indicate it.

Researchers led by Francesco Rubino of King’s College London tested a framework that uses BMI alongside waist circumference or waist-to-height ratio to assess excess body fat. Across the study groups, 5.2% to 8.6% of people classed as overweight by BMI met waist criteria for obesity-level adiposity. Conversely, 1.2% to 3.1% of those classed as obese by BMI had no elevated waist measurements. The percentages refer to different BMI categories, not shares of the entire study population.

The framework then distinguishes between clinical and preclinical obesity. Clinical obesity means excess adiposity accompanied by signs of organ dysfunction; preclinical obesity means excess adiposity without identified dysfunction. The study found that...