The claimEvidence A · guideline-tier
BMI is completely useless
The evidence
BMI (body mass index) is crude for any one person but strongly informative across a population: it shows a robust J-shaped curve with death from any cause (Global BMI Mortality Collaboration, Lancet 2016, 10.6 million people).
The mechanism, in brief
Weight is a metabolic question, not an aesthetic one. What matters is not just the number on the scale but where the fat sits. At the same weight, fat wrapped around the organs (the liver, pancreas and intestines) causes far more trouble than fat under the skin: it is linked to insulin working less well, higher…
Sources (1)
- The Global BMI Mortality Collaboration. (2016). Body-mass index and all-cause mortality: Individual-participant-data meta-analysis of 239 prospective studies in four continents. The Lancet, 388(10046), 776–786. IPD from 239 prospective studies (10.6 million people); primary analyses in 3.95 million never-smokers without chronic disease who survived 5 years. All-cause mortality lowest at BMI 20.0-25.0; HR 1.13 at 18.5-20, 1.51 at 15-18.5, 1.07 at 25-27.5, 1.20 at 27.5-30, 1.45 at 30-35, 1.94 at 35-40, 2.76 at 40-60; per 5 units above 25, HR 1.39 in Europe and east Asia, 1.29 North America, 1.31 Australia/NZ; stronger in younger people and men (abstract, PMID 27423262).