The Obesity Paradox in Type 2 Diabetes and Mortality

The obesity paradox for survival among individuals with type 2 diabetes has been observed in some but not all studies. Conflicting evidence for the role of overweight and obesity in all-cause mortality may largely be a result of differences in study populations, epidemiological methods, and statistical analysis. For example, analyses among populations with long-term prevalent diabetes and the accrual of other chronic health conditions are more likely to observe that the sickest participants have lower body weights, and therefore, relative to normal weight, overweight and even obesity appear advantageous. Other mortality risk factors, such as smoking, also confound the relationship between body weight and survival, but this behavior varies widely in intensity and duration, making it difficult to assess and effectively adjust for in statistical models. Disentangling the potential sources of bias is imperative in understanding the relevance of excess body weight to mortality in diabetes. In this review, we summarize methodological considerations underlying the observed obesity paradox. Based on the available evidence, we conclude that the obesity paradox is likely an artifact of biases, and once these are accounted for, it is evident that compared with normal body weight, excess body weight is associated with a greater mortality risk.