Do GLP-1s cause muscle loss?

The framing matters: GLP-1s don’t attack muscle pharmacologically. They create large, sustained calorie deficits, and the body in deficit pulls from both fat and lean tissue. STEP 1’s body-composition substudy showed roughly 39% of lost mass was lean — typical for unguarded dieting, but at GLP-1 magnitudes (30–50+ lbs) the absolute muscle numbers get meaningful, especially for older adults and repeat dieters. Why it deserves your attention: - Muscle is your metabolic engine; losing it shrinks the maintenance calorie budget you’ll live on afterward. - It’s your blood-sugar sink, strength, and — past 60 — your fall insurance and independence. - Regain after muscle-heavy loss comes back as fat, ratcheting body composition worse with each cycle. The two-part defense (both, not either): 1. Protein floor: ≈1.2–1.6 g/kg of goal body weight daily. On a suppressed appetite this requires engineering, not intention — protein first at every meal, shakes on low days (the how-to). 2. Resistance training 2–3×/week. The mechanical signal that tells the body “this tissue is in use — burn elsewhere.” Bodyweight work, bands, or weights all count; walking does not. Track it crudely but honestly: strength on basic movements and waist-vs-scale. Scale falling with stable strength and shrinking waist = winning. Scale falling with strength collapsing = the deficit is eating muscle; raise protein, slow the loss rate, lift. The pharma pipeline is busy bolting muscle-preserving agents onto GLP-1s (bimagrumab and friends) — which tells you how real the issue is, and that for now, the gym remains the only approved adjunct.