Aim for a BMI of 20–25, and lose excess weight
Mortality was lowest at BMI 20–25. At 27.5–30 it was about 20% higher, at 30–35 about 45% higher, and at 35–40 nearly double. East Asian populations showed particular sensitivity: each additional 5 BMI units above 25 was associated with about 40% higher risk.
What it takes
No required spending, but eating changes and exercise take time daily. This is the chapter's most demanding sustained habit; maintaining weight loss can be harder than losing it.
What you may gain
An individual-participant meta-analysis of 239 prospective observational studies restricted analysis to never-smokers without chronic disease at enrollment who survived at least 5 years afterward. Lowest mortality was at BMI 20–25. HRs were 1.07 at 25–27.5, 1.20 at 27.5–30, 1.45 at 30–35, 1.94 at 35–40, and 2.76 at 40–60: approximately 7%, 20%, 45%, and 94% higher hazards in the first four groups, and 2.76 times the hazard in the last. Above BMI 25, each additional 5 kg/m² in East Asian populations was associated with HR 1.39, or 39% higher mortality.
Context & considerations
Some pooled evidence suggests slightly higher weight predicts longer life: about 6% lower mortality with overweight and 5% lower with mild obesity. The disagreement largely turns on excluding smokers, people already ill and early follow-up, because serious illness can cause weight loss before death. Removing those groups in the 239-study analysis restored the excess risk associated with overweight. No randomized trial cited here establishes that weight loss itself reduces all-cause mortality. Comparing different-sized people does not guarantee the same reduction after losing weight. Meal timing need not be the focus: see breakfast and 16:8 fasting.
Research & references
Global BMI Mortality Collaboration (2016). Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents. Lancet. https://doi.org/10.1016/S0140-6736(16)30175-1 ; Flegal KM et al. (2013). Association of all-cause mortality with overweight and obesity using standard body mass index categories: a systematic review and meta-analysis. JAMA. https://doi.org/10.1001/jama.2012.113905 (the contrasting findings).