- Grade Bcross-filed
Body-composition change on GLP-1 therapy: what newer evidence actually shows
Newer body-composition evidence published in 2024–2026 has substantially revised the lean-mass story on GLP-1 therapy. Conte, Hall, and Klein (JAMA 2024) quantified the fat-mass to fat-free-mass split at roughly 61/39 on semaglutide, 75/25 on tirzepatide, and 67/33 on retatrutide. The SEMALEAN study (Alissou 2026, semaglutide 2.4 mg, 12 months) showed sarcopenic obesity prevalence fell from 49 percent to 33 percent and handgrip strength improved. The earlier 40 percent practitioner estimate has been retired in favor of these verified numbers. A methodological note matters: DEXA-based 'lean mass loss' includes intramuscular fat, which MRI proton-density fat fraction can separate but DEXA cannot. The clinical priority is unchanged — adequate protein (1.2 to 1.6 g/kg of ideal body weight per day) and progressive resistance training are what determine the body-composition outcome.
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- Grade B
Per-meal protein threshold for muscle protein synthesis: the 30 g / leucine-trigger rule
Muscle protein synthesis (MPS) follows a threshold, not a linear dose-response: below roughly 2.5–3 g of leucine per meal (~30 g of high-quality protein), MPS is sub-maximally stimulated. Total daily protein is necessary but insufficient — distribution across meals determines how much of that protein actually builds and preserves lean mass.
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- Grade A
Why the 0.8 g/kg protein RDA systematically underestimates true requirements
The current US protein RDA of 0.8 g/kg/day was derived from short-term nitrogen-balance studies that systematically undercount nitrogen losses and target deficiency prevention, not physiological optimization. Modern tracer methods (IAAO and stable-isotope techniques) consistently yield protein requirements 25–50% higher than nitrogen-balance estimates, placing the true minimum closer to 1.0–1.2 g/kg for sedentary adults and higher for active or aging populations.
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- Grade B
Daily protein target of 1.6 g/kg ideal body weight for patients on GLP-1 medications
Patients on GLP-1 receptor agonists benefit from 1.2–1.6 g of protein per kg of ideal body weight per day, distributed across at least two meals containing ≥30 g each. This target sits well above the 0.8 g/kg RDA, reflects the anabolic demand of a sustained caloric deficit, and is supported by converging meta-analysis, position-stand, and clinical-trial evidence.
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- Grade Bcross-filed
Anabolic resistance in aging and the elevated protein requirement for older adults
Older adults require more protein per meal than younger adults to achieve the same muscle protein synthesis response — a phenomenon known as anabolic resistance. Per-meal requirements rise from roughly 0.24 g/kg in young adults to 0.40 g/kg or higher after age 60, and daily targets of 1.2–1.5 g/kg/day are needed to correct the ~1–2 %/year muscle loss otherwise observed after age 60.
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