Protein After 40

You could be eating a diet that meets every standard nutritional guideline for protein, exercising consistently, and still losing muscle. Not because of a lack of effort, and not because the guidelines are wrong for younger adults. But because after 40, the biological relationship between what you eat and what your muscles do with it changes significantly and the guidance most people are following has not kept pace with that shift.

What's going on?

Sarcopenia, the progressive loss of skeletal muscle mass and function associated with ageing - can begin as early as the fourth decade of life, with losses accelerating meaningfully after 60 (Janssen et al., 2002). The consequences extend well beyond aesthetics. Skeletal muscle is the body's primary site of glucose disposal, its largest reservoir of amino acids, and a critical determinant of metabolic rate, insulin sensitivity, functional independence and fall risk in later life. A 2025 study investigating protein intake in older women with sarcopenia found that a daily intake of at least 1.2g per kilogram of body weight was necessary to prevent measurable deterioration in muscle mass and functional independence, significantly above the standard recommended dietary allowance of 0.8g/kg/day (Ishaq et al., 2025).

The standard RDA was established based on minimum intake to maintain nitrogen balance in healthy young adults. It was never designed as an optimisation target for middle-aged or older populations and a growing body of evidence suggests it is inadequate for that purpose.

Why is this happening?

The mechanism underlying this shift is called anabolic resistance: a blunting of the muscle protein synthesis response to both protein ingestion and exercise that develops progressively with age (Breen & Phillips, 2011). In practical terms, older muscles are less sensitive to the anabolic signal that amino acids provide. Where a 25-year-old might trigger robust muscle protein synthesis from a 20g protein meal, a 55-year-old may require 35-40g from the same meal to achieve a comparable response. The signal is not absent - it is simply attenuated, requiring a stronger stimulus to produce the same effect.

Several factors drive anabolic resistance: declining hormonal milieu, increased systemic inflammation, reduced physical activity levels, impaired digestive efficiency reducing amino acid absorption, and changes in mTOR pathway signalling in muscle cells. Critically, anabolic resistance is not inevitable in its severity. Research consistently shows that resistance exercise and adequate protein intake together can substantially counteract the blunted response - with the combination producing markedly better outcomes than either intervention alone (Breen & Phillips, 2011).

Leucine, the amino acid that acts as the primary trigger for muscle protein synthesis, deserves specific attention here. The leucine threshold required to activate the mTOR pathway and initiate muscle building is higher in older adults than in younger ones. Animal-based proteins - meat, fish, eggs, dairy are generally richer in leucine per gram of protein than plant-based sources. This does not mean plant-based eating is incompatible with muscle maintenance after 40, but it does mean that plant-based older adults need to be more deliberate about total protein quantity and source variety to meet the leucine threshold at each meal.

Top 5 protein priorities after 40

1. Aim for 1.2-1.6g of protein per kilogram of body weight per day. The current RDA of 0.8g/kg is likely insufficient for muscle preservation in middle age and beyond. Most active adults over 40 benefit from the higher end of this range.
2. Distribute protein across three to four meals. As discussed, muscle protein synthesis is an episodic process requiring threshold leucine levels per meal. Concentrating most protein at dinner, which is common, means triggering the muscle-building signal only once daily.
3. Prioritise leucine-rich sources. Eggs, Greek yoghurt, cottage cheese, white fish, chicken and legumes combined with grains all provide meaningful leucine. For plant-based eaters, adding leucine-rich combinations - rice and lentils, tofu with edamame - at each meal is a practical strategy.
4. Combine protein with resistance exercise. The synergistic effect of protein ingestion around resistance training is well-established. Two to three sessions of progressive resistance exercise per week substantially reduces the blunting effect of anabolic resistance.
5. Do not neglect protein at breakfast. Research on protein timing consistently shows that front-loading protein - particularly at breakfast - improves muscle protein synthesis across the day. A protein-rich breakfast anchors the anabolic signal from the first meal rather than the last.

References:

Breen, L., & Phillips, S. M. (2011). Skeletal muscle protein metabolism in the elderly: Interventions to counteract the anabolic resistance of ageing. Nutrition & Metabolism, 8, Article 68. 

Ishaq, I., Noreen, S., Maduabuchi Aja, P., & Atoki, A. V. (2025). Role of protein intake in maintaining muscle mass composition among elderly females suffering from sarcopenia. Frontiers in Nutrition, 12, Article 1595674. 

Janssen, I., Heymsfield, S. B., & Ross, R. (2002). Low relative skeletal muscle mass is associated with functional impairment and physical disability. Journal of the American Geriatrics Society, 50(5), 889-896. 

Stokes, T., Hector, A. J., Morton, R. W., McGlory, C., & Phillips, S. M. (2018). Recent perspectives regarding the role of dietary protein for the promotion of muscle hypertrophy with resistance exercise training. Nutrients, 10(2), Article 180.