Inclusion Criteria:
* Age 30- 60 years
* BMI 27.0-37.0 kg/m² at screening
* English speaking (at this time, MyNetDiary, a food-logging app used for tracking protein-intake, is only set up for English, and our RDN is only capable of providing nutritional counseling in English)
* Received a prescription for tirzepatide, a second-generation oral or injectable dual GIP/GLP-1 receptor agonist (Zepbound/Mounjaro) that is FDA-approved for obesity; and
* Has not yet started tirzepatide and agrees to complete a 4-week run-in period at the initial dose with \<3% weight loss from baseline; OR
* Has initiated tirzepatide and is within the first 4 weeks at the initial dose with \<3% weight loss from pre-treatment baseline.
* On a stable regimen for major chronic conditions (e.g., antihypertensives, lipid-lowering agents, oral antidiabetics, hypothyroidism) for ≥ 8 weeks prior to enrollment.
* Willing and able to:
* (i) Receive high-protein diet counseling and attempt to achieve \~2.5 g/kg FFM /day protein;
* (ii) Attend scheduled nutrition telehealth visits with an RDN;
* (iii) Medically cleared for moderate-intensity resistance training 2 days/week (no condition that would preclude safe participation in either diet-only or diet plus resistance training).
* Willing and able to undergo whole-body MRI at baseline and 6 months without sedation.
* Able to understand procedures and provide written informed consent in English (at this time, MyNetDiary, a food-logging app used for tracking protein-intake, is only set up for English, and our RDN is only capable of providing nutritional counseling in English)
Exclusion Criteria:
* Patients currently prescribed oral or injectable incretin mimetics containing GLP-1RAs, including Exenatide, Liraglutide, Lixisenatide, Dulaglutide, Semaglutide. Participants who are currently prescribed tirzepatide and have been using for \>4 weeks will also be excluded.
* Prior use of incretin mimetics containing GLP-1RAs with \>3% weight loss in a 4-week period
* Lost \>5% body weight in the past 6 months
* Has consistently resistance trained (\>10 sessions) in the last year
* Currently taking medication or supplements that have been shown to impact muscle function and muscle mass in the last 6 months
* Participants who live outside of the tri-state area and/or are not willing to come to New York City for in-person visits outlined
* Plans to be out of town more than 2 consecutive weeks or \>6 weeks total over the next 6 months
* Type 1 or 2 diabetes; uncontrolled diabetes (e.g., HbA1c \> 6.4% if specified); recurrent severe hypoglycemia or hypoglycemia unawareness.
* Moderate-to-severe chronic kidney disease (e.g., eGFR \< 45-60 mL/min/1.73 m2 final cutoff per protocol) or other renal disease
* Decompensated cirrhosis, severe chronic liver disease, or active liver disease
* Unstable cardiovascular disease (e.g., myocardial infarction (MI), stroke, coronary revascularization, or hospitalization for unstable angina or decompensated heart failure (HF) within \<6 months)
* Active malignancy requiring systemic therapy in the past 6-months (excluding non-melanoma skin cancer)
* Serious medical/psychiatric conditions making participation unsafe or likely to impair adherence
* Pregnant, planning pregnancy within 6 months, or breastfeeding; women of childbearing potential unwilling to use effective contraception per institutional/drug-label guidance.
* Conditions requiring protein restriction (e.g., advanced Chronic Kidney Disease (CKD), relevant inborn errors of metabolism).
* Severe, poorly controlled gout/hyperuricemia
* Significant GI disease impairing tolerance or absorption (e.g., active Inflammatory Bowel Disease (IBD) with frequent flares, short bowel syndrome, severe gastroparesis beyond expected GLP-1 effects)
* Severe food allergies or intolerances that preclude a high-protein diet or ingestion of whey or pea protein and associated additives/ingredients of the protein powders used in this study.
* Has or previously had an eating disorder
* Severe musculoskeletal, neuromuscular, or other conditions that preclude moderate-intensity RT
* Advised not to exercise by their general practitioner or medical professional or refusal to obtain medical clearance if indicated by Physical Activity Readiness Questionnaire (PAR-Q) answers
* Standard contraindications to MRI: tattoos with metallic ink, pacemaker, cerebral and/or cochlear implant, metal in the eye, severe claustrophobia, presence of electronic devices or ferromagnetic metallic foreign or implanted objects that could constitute a hazard, inability to lie flat, or any other contraindication for MRI.
* Weight \>200kg, or large body habitus which the MRI scanner cannot accommodate.
* Inability or unwillingness to attend a reasonable proportion of RT sessions and refusal of accommodations
* Concurrent enrollment in another weight management intervention
* Prior bariatric surgery within the past 12 months or planned bariatric surgery within the 6-month study period.
* Active alcohol or drug use disorder
* Significant cognitive impairment or language barrier precluding informed consent or adherence
* Any reason that could compromise the participants' safety, based on the judgment of the investigators and/or clinical coordinators.
