Unsaturated Fatty Acids Enriched-diet to Improve Cardiorespiratory Fitness, Metabolic Flexibility and Glucose Tolerance in Obese Patients

Major Inclusion Criteria: * Body Mass Index (BMI) ≥30 kg/m2 (obesity) or total body fat percentage \>25% in men and \>35% in women * A confirmed clinical diagnosis of stable HF (New York Heart Association \[NYHA\] class II-III) on maximally tolerated heart failure (HF) optimal medical regimen (without major changes in the prior month) * Left Ventricular Ejection Fraction (LVEF)\>50% documented in the prior 12 months Major Exclusion Criteria: * Concomitant conditions or treatment which would affect completion or interpretation of the study (i.e.,physical inability to walk or run on treadmill); * Significant ischemic heart disease, angina, uncontrolled arterial hypertension, atrial fibrillation, moderate to severe valvular disease, chronic pulmonary disease, anemia (Hemoglobin\<10 g/dL) * Electrocardiography (ECG) changes (ischemia or arrhythmias) that limit maximum exertion during cardiopulmonary exercise test * Comorbidity limiting survival * Stage IV-V kidney disease (estimated Glomerular Filtration Rate\<30) * Fluid overload * Pregnancy * Current use of unsaturated fatty acids (UFA) supplement (i.e., omega-3). * Inability to give informed consent