High protein content has become a selling point on foods ranging from breakfast cereals to yoghurts. For anyone hoping to build muscle or stay strong as they age, choosing the product with the most protein can seem sensible. But whether an extra serving will help depends on what they already eat and how they use their muscles.

Someone who regularly lifts weights may benefit from additional protein to support muscle growth. An older person with a small appetite may need help getting enough to maintain strength. Someone already eating enough protein may gain little from adding more.

Understanding those differences can make it easier to decide whether to change your diet, buy a supplement or concentrate on exercise.

Muscle tissue is continually being broken down and rebuilt. Dietary protein supplies amino acids, the small molecules the body uses to make its own proteins, including those in muscle.

Resistance exercise makes muscles work against a load. That load might come from weights or from your own body during an exercise such as press-ups. It stimulates the processes involved in building and repairing muscle, allowing muscles to adapt to repeated demands.

Protein supports this adaptation, but increasing intake does not reproduce the effects of exercise.

A review of 49 trials involving 1,863 participants found that protein supplements produced additional improvements in muscle size and strength during resistance training. Participants were training for at least six weeks. The findings therefore concern protein’s contribution to a training programme, rather than the effects of adding a shake to an otherwise unchanged routine.

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