This study is designed to evaluate the effects of a diet rich in unsaturated fatty acids (UFA)-also known as 'healthy fats'-in patients with obesity and heart failure with preserved ejection fraction (HFpEF) on dietary consumption of UFA as well as fatty acids plasma levels.

The study will evaluate participant's food consumption during 2 different 12-week periods. During one of the 12-week periods, participants will receive specific counseling and instructions on how to increase the consumption of food rich in healthy fats; during the other 12-week period they will receive general dietary recommendations following the Dietary Guidelines for Americans. There will be a 6-week break (washout) between the 12-week periods for a total of study period of 30 weeks. During each 12-week periods, the study will measure the effects of these dietary recommendations on dietary consumption and the fatty acids in their blood (primary endpoints).

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