Anabolic resistance: why muscle gets harder to build and keep with age
Anabolic resistance is the blunting of muscle's normal response to its two main growth signals: dietary protein and exercise. In older adults, the same meal or the same workout produces a weaker rise in muscle protein synthesis than it would in a younger body, so muscle becomes harder to build and easier to lose. The good news is that the resistance is largely surmountable: a bigger per-meal protein dose (around 0.4 g per kg, rich in leucine) and regular resistance training restore much of the lost sensitivity, and the response is intact at any age.
Key facts
- Older muscle plateaus its protein-synthesis response only after about 0.40 g/kg of protein per meal, versus roughly 0.24 g/kg in younger men: about 67% more, weight for weight.1
- The trigger is partly the amino acid leucine; ageing muscle needs more of it per meal to flip the same molecular switch.2
- Just one week of leg immobilisation cut resting myofibrillar synthesis by about 41% and the post-meal response by about 53% in young men, a striking, fast-acting anabolic resistance.4
- Resistance training is the most reliable way to restore sensitivity to protein, and it works into the ninth and tenth decades.6
- Vitamin D helps muscle mainly when you are deficient; omega-3 shows promise but the human outcome data are mixed.119
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What anabolic resistance actually is
Muscle is in constant turnover. All day it is both built (muscle protein synthesis) and broken down (breakdown), and your muscle mass is simply the running balance of the two. The single biggest lever on synthesis is eating protein: a feed of amino acids triggers a brisk, several-hour rise in the rate at which muscle lays down new contractile protein. Mechanical loading from exercise does the same and amplifies the food signal for a day or more afterwards.
Anabolic resistance is when those signals stop landing as hard. The classic demonstration came from Doug Paddon-Jones, Elena Volpi, and colleagues, and most influentially from Daniel Cuthbertson, Michael Rennie, and co-workers, whose 2005 study in The FASEB Journal gave 44 young and older men graded doses of essential amino acids and tracked synthesis. Older muscle showed both reduced sensitivity (it took more amino acids to get going) and a lower ceiling, alongside weaker activation of the mTORC1 signalling pathway that switches synthesis on.3 In other words, the wiring that reads "protein has arrived, start building" has become partly deaf.
Several things plausibly contribute: reduced delivery of amino acids to muscle because blood flow and capillary recruitment fall with age, slower digestion, low-grade chronic inflammation, and fewer functioning satellite (repair) cells. The honest position is that the downstream effect is well established, while the relative weight of each upstream cause is still debated.3 It is also worth noting that anabolic resistance is not purely a number on a birth certificate: much of it tracks with how active and well-fed a person is, which is exactly why it is treatable. For the bigger picture of why tissues respond differently with age, see our health library.
Evidence strength, plainly. That older muscle responds less to a given dose of protein: strong and repeatedly replicated (controlled tracer studies, Cuthbertson 2005, Moore 2015). That a larger, leucine-rich dose closes most of the gap: strong. That resistance training restores sensitivity: strong. Vitamin D for muscle when replete, and omega-3 for muscle outcomes: weak to mixed.
How it drives sarcopenia
Sarcopenia, the progressive loss of muscle mass, strength and function with age, is the visible end-point of anabolic resistance playing out over years. If every protein-containing meal builds a little less muscle than it used to, and every workout (for those who do them) repairs a little less, the daily balance tips gently toward net loss. Over decades that compounds. Most adults lose muscle slowly from around the fifth decade, with the rate accelerating later in life and stepping sharply downward around any illness or hospital stay.
This matters because muscle is not cosmetic. Strength and power are what let you rise from a chair, climb stairs, carry shopping, and catch yourself when you stumble; muscle is also the body's largest site for clearing glucose from the blood, so losing it nudges metabolism the wrong way. Anabolic resistance, low protein intake, and inactivity form a self-reinforcing loop, and the practical insight is that you can interrupt it at more than one point. This article is the mechanistic companion to our pieces on sarcopenia and on protein intake and timing.
The higher per-meal protein threshold
The most useful single number comes from Daniel Moore, Stuart Phillips, and colleagues, published in The Journals of Gerontology: Series A in 2015. They fed young (around 22 years) and older (around 71 years) men graded doses of protein and used breakpoint analysis to find where myofibrillar synthesis plateaued. Younger men maxed out at about 0.24 g/kg of body mass per meal; older men needed about 0.40 g/kg, roughly 67% more.1 This is the mechanistic reason older adults need more protein than the standard 0.8 g/kg/day adult reference intake.
Translated into a day, expert consensus (the PROT-AGE group led by Jurgen Bauer) recommends 1.0 to 1.2 g/kg/day for healthy older adults, rising to 1.2 to 1.5 g/kg/day or more for those who are active or managing illness.5 Crucially, distribution matters as much as the total: hitting the per-meal threshold at each main meal beats loading most of your protein into the evening.
| Body weight | Per meal (~0.4 g/kg) | Daily target (1.2 g/kg) | Everyday equivalent per meal |
|---|---|---|---|
| 60 kg | ~24 g | ~72 g | 3 eggs + Greek yoghurt, or a small chicken breast |
| 70 kg | ~28 g | ~84 g | 120 g salmon, or 30 g whey in milk |
| 80 kg | ~32 g | ~96 g | 130 g chicken or tofu plus a side of beans |
| 90 kg | ~36 g | ~108 g | 150 g lean meat or fish, plus dairy |
Most older adults already eat enough protein at dinner but fall well short at breakfast. Fixing breakfast is often the highest-yield change.
The leucine trigger
Not all protein is equal for this signal. Of the amino acids, leucine is the one that most directly activates mTORC1 and kick-starts synthesis, and ageing muscle appears to need a higher leucine concentration to reach the same threshold. The practical figure that emerges from the literature is roughly 2.5 to 3 g of leucine per meal for older adults, against perhaps 2 g in the young.2 Whey, dairy, eggs, meat, fish, and soya are the densest sources.
Stuart Phillips' group has tested whether topping up leucine can rescue an otherwise sub-threshold meal. Sarah Devries and colleagues, writing in The Journal of Nutrition in 2018, gave older women a small 15 g protein dose and found that enriching it to 4.2 g of leucine (versus 1.3 g) produced a significantly stronger synthesis response: leucine content, not just total protein, drove the effect.2 The honest caveat is that these are short-term molecular studies; whether sprinkling leucine on small meals translates into more muscle over months, in people who could instead simply eat a bigger protein portion, is far less certain. For most people, a properly sized whole-food meal already clears the leucine bar without any powder.
A note on protein and kidneys. In people with healthy kidneys, intakes around 1.2 to 1.6 g/kg/day are well tolerated and not shown to cause harm. If you have chronic kidney disease or another condition affecting kidney function, do not raise protein without medical advice, as your target may need to be individualised. Isolated high-dose leucine or branched-chain amino acid supplements are best avoided unless guided, because skewing one amino acid can be counter-productive.
Resistance training restores sensitivity
If diet sets the raw materials, exercise rebuilds the machinery that reads the signal. A single bout of resistance exercise sensitises muscle to protein for 24 hours or more, and repeated training partly reverses anabolic resistance: trained older muscle responds to a meal more like younger muscle does. This is why training is the foundation rather than an optional extra.
The clinical payoff is large and well documented. Across randomised trials and meta-analyses, progressive resistance training improves strength and physical function in older adults, including frail people in their eighties and nineties, with gains in muscle mass that are real but more variable.6 "Progressive" is the operative word: muscle adapts only when the challenge gradually rises, whether through heavier weights, bands, or harder bodyweight moves. Adding adequate protein to training improves the result further; Naomi Cermak and colleagues' meta-analysis found protein supplementation augmented gains in lean mass and strength alongside resistance training in both younger and older people.7
In UK terms, the NHS advises strength activities working all major muscle groups on at least two days a week, done to the point where you need a short rest before repeating.8 Start light, learn the movements, and add load slowly. If you want to see where protein or creatine might fit around a training plan, our stack builder keeps it simple.
Disuse: the hidden accelerator
The flip side of training is disuse, and this is where anabolic resistance turns dangerous quickly. When a limb is rested, muscle does not just stop growing; it actively becomes resistant to protein. Marlou Dirks, Benjamin Wall, Luc van Loon, and colleagues, writing in the American Journal of Physiology in 2016, immobilised one leg in young men for a week. Resting myofibrillar synthesis fell by about 41%, and the post-meal response by about 53%: a meal that should have built muscle now barely registered.4 A systematic review by Konstantinos Prokopidis and colleagues confirms that bed rest and immobilisation reliably suppress synthesis, and that the effect is more pronounced in older adults, in whom anabolic resistance is already present.10
The real-world version is a "muscle catabolic crisis": a chest infection, a fall, a hip operation, or a week off your feet with flu can erase months of slow progress, and older bodies struggle to rebuild it afterwards. Two defences help. First, protect protein intake during illness, even when appetite is low, because needs rise rather than fall. Second, move as soon as it is safe: even light loading and standing blunt the loss. Encouragingly, recent work suggests a single bout of resistance exercise before a planned period of bed rest can partly shield older muscle from the decline, which is relevant for anyone facing elective surgery. Staying generally active is the cheapest insurance there is; see our getting-started guide for building the habit gradually.
Vitamin D and omega-3, honestly
These two get heavily marketed for "muscle ageing," so here is the calibrated picture.
Vitamin D. The clearest benefit for muscle strength and falls is in people who are genuinely deficient; correcting a true deficiency can help, but routine supplementation on top of already-adequate levels has not reliably improved strength in trials, and meta-analyses are inconsistent.11 In the UK, where sunlight is weak from October to March, official advice is that everyone should consider a daily 10 microgram (400 IU) supplement over autumn and winter, and year-round if housebound or rarely outdoors.11 Sensible to correct a low level; little reason to mega-dose.
Omega-3. The mechanistic case is genuinely interesting. Gordon Smith, Bettina Mittendorfer, and colleagues showed in a 2011 randomised trial (16 older adults) that 8 weeks of fish oil augmented the synthesis response to amino acids and insulin, with greater mTOR signalling.9 A later trial from the same group (2015) reported that 6 months of fish oil (about 4 g/day) modestly increased thigh muscle volume and grip strength versus corn oil.9 But other randomised trials, including a 2021 trial by Caoileann Murphy and colleagues in well-nourished older adults given leucine-enriched protein with or without fish oil, have found no clear added benefit for muscle mass, strength or physical performance.12 The honest summary: promising mechanism, mixed outcomes, not a substitute for protein and training. There may be a fair case for an omega-3 supplement on cardiovascular or dietary-intake grounds, but framing it as a muscle-builder oversells the evidence.
Two cheap, proven levers (training and adequate, well-distributed protein) do the overwhelming majority of the work. Supplements are at best a small top-up, and only worth the spend once the basics are genuinely in place.
Practical steps
Anabolic resistance is real, but it is one of the more reversible features of ageing. You are not fighting biology so much as feeding and loading muscle hard enough to be heard.
What to ask your GP or pharmacist
- My grip feels weaker and rising from a chair is harder: could this be early muscle loss, and can we check it?
- Could you measure my grip strength, or watch a chair-stand or walking-speed test?
- Is my vitamin D level worth checking, given how little I am outdoors?
- I have a procedure or illness coming up: how do I protect my muscle and move safely afterwards?
- Do any of my conditions or medicines change how much protein is safe for me?
- Can you refer me to a physiotherapist or a local strength-and-balance class?
The one thing that never works is waiting. Muscle keeps responding to a sensible training and protein stimulus throughout life; meaningful strength gains have been shown even in nursing-home residents in their nineties.
References
- Moore DR, Churchward-Venne TA, Witard O, Breen L, Burd NA, Tipton KD, Phillips SM. Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men. J Gerontol A Biol Sci Med Sci. 2015;70(1):57-62. Oxford Academic.
- Devries MC, McGlory C, Bolster DR, et al. Leucine, not total protein, content of a supplement is the primary determinant of muscle protein anabolic responses in healthy older women. J Nutr. 2018;148(7):1088-1095. jn.nutrition.org.
- Cuthbertson D, Smith K, Babraj J, et al. Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle. FASEB J. 2005;19(3):422-424. PMID 15596483. See also Breen L, Phillips SM. Nutr Metab (Lond). 2011;8:68. PMC3201893.
- Dirks ML, Wall BT, Nilwik R, et al. Short-term muscle disuse lowers myofibrillar protein synthesis rates and induces anabolic resistance to protein ingestion. Am J Physiol Endocrinol Metab. 2016;310(2):E137-E147. APS Journals.
- 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. ScienceDirect.
- Talar K, Hernandez-Belmonte A, Vetrovsky T, et al. Effects of resistance training in older adults with sarcopenia: a systematic review and meta-analysis of randomised controlled trials. Eur Rev Aging Phys Act. 2021. PMC8588688.
- Cermak NM, Res PT, de Groot LC, Saris WH, van Loon LJ. 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. PMID 23134885.
- NHS. Physical activity guidelines for older adults. nhs.uk.
- Smith GI, Atherton P, Reeds DN, et al. Dietary omega-3 fatty acid supplementation increases the rate of muscle protein synthesis in older adults: a randomized controlled trial. Am J Clin Nutr. 2011;93(2):402-412. PMC3021432. Muscle-mass follow-up: Smith GI, et al. Am J Clin Nutr. 2015;102(1):115-122.
- Prokopidis K, Morgan PT, Veronese N, et al. The effect of bed rest, unilateral limb immobilization and head-down tilt on muscle protein synthesis: a systematic review and meta-analysis. Exp Physiol. Wiley Online Library.
- NHS. Vitamin D: how much you need and supplements in autumn and winter. nhs.uk. Trial context: Beaudart C, et al. J Clin Endocrinol Metab. 2014;99(11):4336-4345.
- Murphy CH, Flanagan EM, De Vito G, et al. Does supplementation with leucine-enriched protein alone and in combination with fish-oil-derived n-3 PUFA affect muscle mass, strength, physical performance, and muscle protein synthesis in well-nourished older adults? A randomized, double-blind, placebo-controlled trial. Am J Clin Nutr. 2021;113(6):1411-1427. ajcn.nutrition.org.
This article is educational and does not constitute medical advice, diagnosis, or a treatment recommendation. Medication uses described as “off-label” are not licensed for that purpose in the UK and should only be considered under qualified clinical supervision. Always speak to your GP, pharmacist, or a registered specialist before starting, stopping, or changing any treatment. If you have severe or alarm symptoms - unintentional weight loss, blood in your stool, difficulty swallowing, persistent vomiting, a fever, or severe pain - seek urgent medical care.