Protein for Aging Muscle: The Sarcopenia Dose Is Higher Than You Think

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Sarcopenia — the age-related loss of muscle mass, strength, and function — is one of the most consequential and most preventable drivers of disability after about age 65. Protein supplementation has moved from a bodybuilder topic to a routine part of geriatric care, and the current expert consensus supports daily intakes well above the standard RDA.

The RDA is a floor, not a target

The US RDA for protein, 0.8 g/kg/day, was derived from short-term nitrogen-balance studies in younger adults and assumes excellent protein quality. The international PROT-AGE Study Group recommends at least 1.0–1.2 g/kg/day for healthy older adults, 1.2 g/kg/day or more for those who exercise, and 1.2–1.5 g/kg/day for older adults with acute or chronic disease — with the exception of severe kidney disease (eGFR <30 not on dialysis), where intakes are limited (Bauer 2013; PMID 23867520; DOI 10.1016/j.jamda.2013.05.021). The European Working Group on Sarcopenia in Older People (EWGSOP2) endorses similar targets and now defines sarcopenia primarily by low muscle strength, with low quantity used for confirmation (Cruz-Jentoft 2019; PMID 30312372; DOI 10.1093/ageing/afy169).

The leucine threshold

Aging muscle develops "anabolic resistance" — older adults need more leucine per meal than younger adults to switch on muscle protein synthesis. Stable-isotope work in older men has placed the per-meal leucine threshold at roughly 2.5–3 g, which corresponds to about 25–40 g of high-quality protein per meal. Distributing protein across three or four meals so each one hits this threshold is more effective than loading the daily total into dinner.

Whey, casein, or plant

Whey is the most studied protein in sarcopenia trials; it has the highest leucine content (~10–11% of amino acids) and absorbs quickly, which suits the per-meal leucine-threshold approach. Casein digests more slowly and gives a longer amino-acid release, which is why it's often used at bedtime. Plant proteins (soy, pea) can do the job but usually need 20–30% more grams to match the leucine load, and a blend (e.g., pea + rice) is preferred over a single source.

Adding resistance training is what changes the trajectory

Protein supplementation alone produces small effects; combined with progressive resistance training the effect is meaningful. A meta-analysis of 49 RCTs (1,863 healthy adults) found that adding protein supplementation to resistance training significantly increased fat-free mass (mean +0.30 kg vs control), 1-rep-max strength, and muscle fibre cross-sectional area, with the benefit shrinking as participant age rose; benefits plateaued at total intakes above ~1.6 g/kg/day (Morton 2018; PMID 28698222; DOI 10.1136/bjsports-2017-097608). Training provides the mechanical signal; protein supplies the building blocks. Neither alone delivers what the combination does.

Kidney safety

In older adults with normal kidney function, intakes up to ~1.5 g/kg/day have not been shown to harm kidney function in trials. In moderate-to-severe chronic kidney disease (eGFR <30 mL/min/1.73 m², not on dialysis) protein is restricted, with targets individualised by a renal dietitian. For everyone else over 65 on sustained high-protein intake, an annual basic metabolic panel including eGFR is a reasonable baseline check.