This study is testing how different types of protein - from red meat, legumes (like lentils and beans), or a mix of both - affect muscle strength, body composition, and metabolic health in older adults with obesity who are also at risk for sarcopenia (loss of muscle mass and function). Participants will follow a personalized weight loss diet with one high-protein meal each day that includes either red meat, legumes, or both, along with a home-based strength training program. The study will last three months and will include health assessments such as blood tests, muscle and fat measurements, and physical function tests. The goal is to find out which type of protein source is most helpful for improving strength, reducing body fat, and supporting healthy aging.

Inclusion Criteria:

• Aged 55 years or older.
• Diagnosed with obesity.
• At risk for sarcopenia, based on at least one of the following: Low score on the validated SARC-F-calf questionnaire (as suggested in prior studies). More than one comorbidity associated with sarcopenic obesity (e.g., diabetes, osteoporosis, cardiovascular disease, etc.). Polypharmacy: taking 8 or more prescribed medications. Evidence of strength or functional impairment, assessed using validated measurements at the baseline visit.

Exclusion Criteria:

• Recent use of steroid agents within the past 6 months (replacement therapy is allowed).
• Uncorrected hypothyroidism: TSH > 6 mIU/L.
• Diagnosis of malignancy within the past 5 years, except for non-melanoma skin cancer.
• Chronic kidney disease (CKD) at stage >1 (due to protein restriction needs).
• Recent (≤6 months) or unstable cardiovascular condition, or NYHA Class III or higher congestive heart failure.
• Currently performing resistance training.
• Currently undergoing nutritional therapy, have recently changed diet (<1 month), or are enrolled in active weight-loss programs or therapies (including lifestyle and/or pharmacotherapy). Note: Patients stable on GLP-1 agonists or other pharmacotherapy are eligible.
• Vegetarians/vegans, or individuals with aversion or allergy to all legumes or all red meat products.
• Habitual consumption of more than 3 servings/week of either legumes or red meat.
• Other medical, psychiatric conditions, or lab abnormalities that may pose a risk to participation.

Investigators, physical trainers, and outcomes assessors are blinded to group allocation. Participants and dietitians delivering the dietary intervention are not blinded, due to the nature of individualized nutrition counseling. All meals are coded neutrally to preserve blinding for trainers and assessors.