Rapid weight loss reduces lean mass alongside fat — roughly 70:30 ratio. Biologically wasteful and clinically problematic, especially at 40+.
The 70:30 problem
Without intervention, ~30% of weight lost during rapid loss is lean mass — muscle, bone, organ tissue. Worsens with age, severity of deficit, and inactivity.
The fix — two components
Protein
1.6–2.0 g/kg target body weight. Higher for 60+ (consider 1.8–2.2 g/kg). Spread across meals.
Resistance training
2–3 sessions/wk, progressive overload, major muscle groups. The signal that tells the body to retain muscle during deficit.
What doesn't work
- Aerobic alone — doesn't preserve muscle
- Protein alone without resistance — partial benefit
- Walking only — insufficient signal
Why it matters at 40+
Adults lose ~1% muscle/year after 30. GLP-1 weight loss without resistance training compresses 5+ years of normal muscle loss into months. Downstream consequences (sarcopenia, falls, frailty) clinically meaningful.
Tracking
DEXA or InBody at baseline and 3, 6, 12 months if accessible. Proxies: grip strength, ability to perform standard resistance lifts, clothing fit in legs/arms vs midsection.