The goal of this clinical trial is to evaluate the effects of a high-protein diet with or without HMB supplementation compared with a normoprotein diet on clinical, nutritional, and functional outcomes in patients with heart failure. The main questions it aims to answer are:

1. Does a normocaloric high-protein diet improve muscle mass, muscle strength, and physical function compared with a normocaloric normoprotein diet after 8 weeks?
2. Does adding 3 g/day of β-hydroxy-β-methylbutyrate (HMB) to a normocaloric high-protein diet provide additional benefits for muscle mass, muscle strength, and physical function compared with a normocaloric high-protein diet alone?
3. Do these nutritional interventions improve renal function, inflammatory and clinical biomarkers, functional status, and quality of life after 8 weeks?

Researchers will compare three groups (normocaloric normoprotein diet, normocaloric high-protein diet, and normocaloric high-protein diet plus HMB supplementation) to determine the effects of these interventions on clinical, nutritional, and functional outcomes.

Participants will:

• Be randomly assigned to one of the three study groups
• Receive individualized dietary counseling according to their assigned intervention
• Receive one study sachet daily containing either an HMB-enriched nutritional supplement (providing 3 g/day of HMB) or a matched placebo, according to the assigned study group
• Undergo assessments of muscle mass, muscle strength, physical function, renal function, inflammatory and clinical biomarkers, and quality of life at baseline, 4 weeks, and 8 weeks