The interaction of cardiorespiratory fitness with obesity and the obesity paradox in cardiovascular disease

Overweight and obesity are well-established risk factors for most cardiovascular diseases (CVD), including coronary heart disease (CHD), heart failure (HF), and atrial fibrillation. Despite the strong link between excess adiposity and risk of CVD, growing evidence has demonstrated an obesity paradox in patients with CVD. This phenomenon is characterized by a better prognosis in overweight and mildly obese CVD patients than their leaner counterparts. Moreover, the worst outcomes are often incurred by underweight CVD patients, followed by those of normal weight or severely obese. The obesity paradox is now a well-established phenomenon across different types of CVD, and it occurs regardless of age and ethnicity of patients, and severity of CVD. Physical inactivity and low cardiorespiratory fitness (CRF) have long been recognized as major risk factors for CVD. In contrast, high levels of physical activity (PA) and CRF largely neutralize the adverse effects of excess adiposity and other traditional CVD risk factors, including hypertension, metabolic syndrome, and type-2 diabetes. Higher CRF also results in better CVD outcomes across different BMI groups and significantly alters the obesity paradox in patients with HF and CHD. Prognostic benefits of overweight/obesity tend to be limited to unfit patients with HF and CHD, and the obesity paradox usually disappears with improved levels of CRF. Nevertheless, increased PA and exercise training, to maintain or improve CRF, are effective, safe, and proven strategies for primary and secondary prevention of CVD in all weight groups. In this review, we discuss the current concepts of individual and combined contributions of fatness and fitness to CVD risk and prognosis. We then examine the influence of fitness on the obesity paradox in individuals with CVD