Overview
- The Nature study, published 11 November 2026, tested the Lancet Commission’s two-step framework in 844,108 adults from China, the UK, the US and Spain and found it diagnosed obesity more accurately than BMI alone.
- The framework first confirms excess body fat using waist measures such as waist circumference or waist-to-height ratio and then labels cases as clinical obesity when at least one of 18 obesity-related organ or functional impairments is present and preclinical obesity when those impairments are absent.
- BMI alone missed up to 8.6% of people with obesity-level body fat and overcalled obesity in up to 3.1% of people, while adding waist measures raised estimated obesity prevalence by about 3.3 to 7.4 percentage points across cohorts.
- People classified with clinical obesity had about a 69% higher all-cause mortality risk and those with preclinical obesity had about a 19% higher risk compared with people without excess fat or dysfunction, and most people with preclinical obesity did not progress to clinical obesity over ten years.
- Wider adoption could change who is labeled and who becomes eligible for treatments, but the study is observational so clinicians will need practical workflow tests, agreed criteria, ethnicity-specific cutoffs and training before the definition can reshape care and policy.