Protein After 40: Why Your Muscle, Metabolism and Healthy Ageing Depend On It

If there's one piece of nutrition advice I'd give almost everyone over 40, it's this: pay attention to your protein. Not because of a fad, but because the research on muscle, metabolism and ageing is genuinely compelling — and because the official "minimum" most of us grew up with was never designed to keep us strong into our 70s and 80s. As an Accredited Practising Dietitian (and a biohacker at heart), I want to walk you through what the evidence really says, without the hype.

The quiet problem: anabolic resistance

From around our 30s, we gradually lose skeletal muscle — a process called sarcopenia — and with it, strength, metabolic flexibility and a surprising amount of long-term independence. Part of why this happens is something researchers call anabolic resistance: an ageing muscle simply responds less to the same dose of protein than a younger one does. An international expert group (the PROT-AGE Study Group) reviewed this in detail and concluded that older adults need more dietary protein than younger adults to offset these age-related changes and to recover well from illness.^[1]

How much do you actually need?

The classic Recommended Dietary Allowance — about 0.8 g of protein per kilogram of body weight per day — is set to prevent deficiency in the general adult population. It is not an "optimal" target for healthy ageing. Two of the most respected evidence reviews in this area land in close agreement:

• The PROT-AGE position paper recommends 1.0–1.2 g/kg/day for healthy older adults, rising to 1.2–1.5 g/kg/day for those who are active or managing acute or chronic illness.^[1]
• The ESPEN Expert Group (European Society for Clinical Nutrition and Metabolism) reached essentially the same conclusion: at least 1.0–1.2 g/kg/day for healthy older people, and 1.2–1.5 g/kg/day with illness or malnutrition risk — ideally combined with exercise.^[2]

To make that concrete: a healthy 70 kg adult aiming for 1.2 g/kg is looking at roughly 84 g of protein a day — meaningfully more than many people eat, particularly at breakfast.

It's not just how much — it's when

Here's a detail I find genuinely useful in clinic. Most people back-load their protein: a little at breakfast, a bit more at lunch, then a large hit at dinner. A controlled study published in The Journal of Nutrition compared an even protein distribution (around 30 g at each of breakfast, lunch and dinner) with the typical skewed pattern, keeping total protein identical. Spreading it evenly produced a 25% higher 24-hour muscle protein synthesis rate.^[3]

Why? Each meal needs to clear a certain threshold to meaningfully "switch on" muscle building — and that threshold appears higher in older adults thanks to anabolic resistance. Practically, that means aiming for roughly 25–35 g of quality protein per main meal rather than saving it all for dinner.

Protein plus resistance training: the real multiplier

Protein on its own helps, but it works far better alongside resistance (strength) training. A large systematic review and meta-analysis in the British Journal of Sports Medicine pooled 49 studies and over 1,800 participants. Protein supplementation significantly increased gains in strength, fat-free mass and muscle size during prolonged resistance training. Two findings stood out: the benefit of added protein plateaued at a total intake of about 1.62 g/kg/day, and while the effect was somewhat blunted with age, it was still clearly present in older adults.^[4] An earlier meta-analysis reached the same broad conclusion — protein supplementation augments the muscle and strength adaptations to resistance training, including in older people.^[5]

In other words: the lifting tells the muscle to grow; the protein gives it the raw material. You want both.

Putting it together

• Target around 1.2 g/kg/day if you're a healthy older adult — more (1.2–1.5 g/kg) if you're training hard or recovering from illness. There's little additional muscle benefit beyond ~1.6 g/kg/day for most people.^[1][2][4]
• Spread it across the day — roughly 25–35 g per meal, including breakfast.^[3]
• Prioritise quality, leucine-rich sources: dairy, eggs, fish, lean meat and soy are particularly effective; combine legumes with grains if you're plant-based.
• Pair it with resistance training at least twice a week — this is where the magic happens.^[4][5]

A quick, important caveat: if you have kidney disease, don't increase protein without individualised advice — protein targets change in that context. And these are general recommendations, not a substitute for a plan built around you. If you'd like that, that's exactly what I do.

References

1. Bauer J, Biolo G, Cederholm T, et al. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. J Am Med Dir Assoc. 2013;14(8):542–559. PubMed
2. Deutz NEP, Bauer JM, Barazzoni R, et al. Protein intake and exercise for optimal muscle function with aging: recommendations from the ESPEN Expert Group. Clin Nutr. 2014;33(6):929–936. PMC
3. Mamerow MM, Mettler JA, English KL, et al. Dietary protein distribution positively influences 24-h muscle protein synthesis in healthy adults. J Nutr. 2014;144(6):876–880. PubMed
4. Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376–384. PubMed
5. Cermak NM, Res PT, de Groot LCPGM, et al. Protein supplementation augments the adaptive response of skeletal muscle to resistance-type exercise training: a meta-analysis. Am J Clin Nutr. 2012;96(6):1454–1464. PubMed