Causes and consequences of the reverse epidemiology of body mass index in dialysis patients

A high body mass index (BMI) has been consistently shown to have a strong predictive correlation to decreased all-cause and cardiovascular mortality in maintenance hemodialysis (MHD) patients, ie, individuals with advanced chronic kidney disease undergoing maintenance dialysis. Indeed, according to some but not all, even morbid obesity (BMI > 35 kg/m²) confers survival advantages. Among the possible causes of reverse epidemiology of BMI are the following: (1) stable hemodynamic status in obesity, (2) higher concentrations of receptors of tumor necrosis factor-α and neurohormonal alterations in obesity, (3) time discrepancies among competitive risk factors, and (4) malnutrition–inflammation complex syndrome. The reverse epidemiology of BMI may have significant clinical and public health implications because interventions that can increase body weight and BMI in dialysis patients may improve survival in these individuals. However, this hypothesis should be tested in well-designed randomized trials. Until then, it is not reasonable to advocate obesity in MHD patients. On the other hand, categorically discrediting the theory of reverse epidemiology and calling it spurious without examining the true effect of weight-gaining interventions on the survival of dialysis patients is not scientifically or ethically appropriate.