Obesity and prognosis in chronic diseases--impact of cardiorespiratory fitness in the obesity paradox.

The effects of overweight and obesity on chronic diseases, particularly on cardiovascular disease (CVD), and its impact on increasing CVD risk factors and total CVD are reviewed. However despite the adverse effects of obesity on CVD risk factors and CVD, obesity has a surprising association with prognosis in patients with established diseases, often showing an "obesity paradox," [corrected] where overweight (body mass index (BMI), 25 to 29.9 kg·m(-2)) and obese patients (BMI, ≥30 kg·m(-2)) with established CVD frequently have a better prognosis than that of their leaner counterparts (BMI, <25 kg·m(-2)) with the same diseases. Fitness-versus-fatness debate is summarized also, including the critical role that fitness plays to alter the relationship between adiposity and subsequent prognosis.