Body Mass Index, Obesity, and Mortality– Part I

The association of obesity with mortality has been the subject of scientific investigation for centuries. Although historical observations, as well as more recent quantitative analyses, demonstrate a relationship of obesity with early death, there remain questions about the degree of the association and how it may vary with age, diet, physical activity, and other life circumstances. The relationship between body mass index (BMI) and mortality is “U-shaped,” with the lowest mortality rate observed at a mildly overweight BMI. Many potential explanations have been postulated for higher mortality at both lower and higher levels of BMI, such as occult disease in those at low BMI; difference across categories in weight variability, smoking, and/or distribution of body fat; and the “fit but fat” phenotype. This review discusses some of the continuing questions and hypotheses surrounding the relationship of BMI with mortality and identifies additional research needed.