Protein powder without the lifting does nothing for ageing muscle

Muscle mass and strength decline with age, and in its more severe form this loss is called sarcopenia, a condition that threatens independence and quality of life. Eating more protein is widely suggested as a way to slow or reverse the decline, yet trials testing the idea have produced inconsistent results. A key unresolved question is whether protein helps on its own, or only when muscles are given a reason to grow through resistance exercise. This review pulled together the randomised evidence to answer exactly that.

The researchers searched PubMed, Medline, Web of Science and Cochrane CENTRAL for randomised controlled trials published from January 1990 to July 2021. Eligible trials tested whole protein supplements or higher-protein diets in adults with a mean age of at least 50, without amino acids or other supplements known to stimulate muscle growth, either alone or combined with resistance exercise. Outcomes were total lean body mass, appendicular lean mass (the muscle on the arms and legs), handgrip strength and knee extension strength. Twenty-eight studies met the criteria.

Pooled across all trials, extra protein on its own produced no significant improvement in total lean mass, limb lean mass, handgrip strength or knee extension strength. The picture changed in trials that also used resistance exercise: there, higher protein intake produced significant gains in appendicular lean mass and handgrip strength compared with lower-protein controls. Subgroup analysis found the lean mass benefit was concentrated in sarcopenic or frail populations. Age, per-meal protein dose, trial duration and baseline protein intake showed no significant relationship with any outcome, and most of the 28 studies had some risk of bias.

This fits a broader pattern in muscle physiology: protein supplies the building material, but resistance training supplies the stimulus, and the evidence keeps suggesting the material matters most when the stimulus is present. It also helps explain why earlier protein trials disagreed, since many did not include training. The finding that frail and sarcopenic groups benefited most leaves an open question about whether healthier older adults, who may already eat enough protein, have less to gain. The wide disagreement between trials means the true size of the benefit remains uncertain.

For older adults, this is a reason to think of protein and resistance training as a package rather than a choice, since the pooled evidence found protein alone moved none of the muscle or strength outcomes. It is also a useful corrective to the idea that a daily shake by itself defends ageing muscle. The analysis cannot say what intake is ideal, because per-meal dose showed no clear relationship with outcomes here. The trials studied adults aged 50 and over, so results in younger groups may differ.