Random-effects summary all-cause mortality HRs for overweight (BMI of 25-<30), obesity (BMI of ≥30), grade 1 obesity (BMI of 30-<35), and grades 2 and 3 obesity (BMI of ≥35) were calculated relative to normal weight (BMI of 18.5-<25). The summary HRs were 0.94 (95% CI, 0.91-0.96) for overweight, 1.18 (95% CI, 1.12-1.25) for obesity (all grades combined), 0.95 (95% CI, 0.88-1.01) for grade 1 obesity, and 1.29 (95% CI, 1.18-1.41) for grades 2 and 3 obesity.
Relative to normal weight, both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality. However, grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality.
In an accompanying editorial the authors discuss that this question has engaged the interest of the public, health care professionals, and a wide range of clinical investigators and has profound health, social, and economic implications for individuals, communities, and the population as a whole. (2)
1. Association of all-cause mortality with overweight and obesity using standard body mass index categories: a systematic review and meta-analysis.Flegal KM, Kit BK, Orpana H, Graubard BI. JAMA. 2013;309:71-82.
2. Heymsfield SB, Cefalu WT. Does body mass index adequately convey a patient's mortality risk? JAMA. 2013;309:87-8. doi: 10.1001/jama.2012.185445.