Ketogenic Diet vs Mixed Diet in Patients With Heart Failure

This study compares a ketogenic diet (very low carbohydrate, high fat) to a standard mixed diet in people with heart failure and preserved pumping function. Researchers want to know if reducing carbs and increasing fat intake can improve exercise capacity and heart function. **You may be eligible if...** - You are between 18 and 80 years old - You have heart failure with a pumping function of 40% or better - You have had stable heart failure symptoms for at least 3 months - You are overweight (BMI 25 or above), have Type 2 diabetes, prediabetes, or metabolic syndrome - You are able to do a treadmill exercise test - Your weight has been stable for the past 3 months **You may NOT be eligible if...** - You have Type 1 diabetes or a history of diabetic ketoacidosis - You have a pacemaker, defibrillator, or other implanted cardiac device - You are claustrophobic or have metal implants that prevent MRI - You have serious kidney disease (eGFR below 30) - You have had a heart attack or major cardiac procedure in the last 30 days - You are currently on a low-carb diet - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.