This study looks at the effects of weight loss in people who have heart failure with reduced ejection fraction (HFpEF) and are overweight or obese.

The main questions it aims to answer are whether weight loss in this group of people improves:

• The heart's shape and how well it pumps blood
• The person's quality of life and how much they can exercise

Participants will attend 2 study visits, separated by 3-6 months. The intervention period takes place in between the 2 study visits.

Each study visit may involve measurements including:

Symptom and quality of life questionnaires Body measurements such as height and weight Blood tests Ultrasound scans of the heart (echocardiogram) Magnetic Resonance Imaging (MRI) scans of the heart 6 minute walk test Participants are randomly allocated (in other words, by lottery) to either 'diet' or 'control' groups. The control group will continue standard care.

The diet group will be enrolled in a weight loss program supervised by the study team. Participants in the diet group will replace their usual meals with meal replacement products specifically designed to deliver a low calorie diet for weight loss. The products will consist of formula soups, shakes and porridges. This diet would last 8 weeks, followed by a guided period of food reintroduction and maintenance.

Inclusion Criteria:

• Heart failure determined by left ventricular ejection fraction 20-45%
• Body mass index > 27.5kg/m^2

Exclusion Criteria:

• Contraindications to magnetic resonance imaging
• NYHA class IV
• Pregnancy, planned pregnancy or lactating
• Significant valvular, ischemic, infiltrative or other potentially confounding cardiac disease
• Any other conditions which may potentially compromise the safety or scientific validity of the study