Protein

Protein is the single nutrient where naïve reading of cohort data and naïve reading of mechanistic biology give the most contradictory advice. Cohorts repeatedly suggest "low protein extends lifespan." Trainers, sports scientists, and the geriatric literature insist midlife and older adults need more protein, not less. Both readings are correct in their own demographic, and the 2024–2026 mechanistic literature now explains why. The article walks the resolved version.

The biochemistry, briefly

Two opposing nutrient-sensing enzymes sit at the centre of the cell's anabolic-vs-catabolic decision. The full mechanism — and how it sets the rate of ageing — lives under deregulated nutrient sensing; what follows is the short version the protein argument needs.

mTOR (mechanistic target of rapamycin) — the anabolic, pro-growth sensor. Its mTORC1 complex integrates growth factors, energy status, and — most importantly here — amino acid availability, and the single most potent nutrient trigger is the branched-chain amino acid leucine.^[1] Once active, mTORC1 drives protein synthesis and the building of new ribosomes — and simultaneously switches off autophagy, the cell's recycling-and-cleanup program.^[2]

AMPK (AMP-activated protein kinase) — the catabolic, low-fuel sensor. It responds to a falling energy charge (fasting, caloric deficit, mechanical loading), and when active it stimulates glucose uptake, fat oxidation, and the building of new mitochondria, switches mTORC1 off, and initiates autophagy.^[3]

The hyperfunction theory of ageing — that ageing is the unabated continuation of growth programs into late life — treats chronic mTORC1 activation as the central pathological signal, with AMPK activation (via fasting, exercise, or a low energy state) as its physiological counterweight.^[4] Both extremes are pathological: continuous anabolic drive accelerates atherosclerosis, cancer, and senescence; continuous catabolic drive produces frailty, sarcopenia, and immune failure.

The leucine threshold and the macrophage problem

Two numbers anchor everything that follows.

Number one — the "muscle full" threshold. Maximally stimulating muscle protein synthesis (MPS) in a single meal requires roughly 2.5–3.0 g of leucine reaching the systemic circulation, which is delivered by 0.4 g of high-quality protein per kg body weight (~25–30 g for an average adult) per meal.^[5] Beyond this dose, the efficiency of conversion to MPS falls off. Doubling the protein in one sitting doesn't double the synthesis response.^[6]

This is best read as an efficiency threshold, not an absorptive or anabolic hard ceiling (Moderate). A rigorous quadruple-isotope tracer trial in young active men found that 100 g of protein after exercise produced a greater and longer-lasting myofibrillar response than 25 g — roughly 20% higher synthesis over the first 4 hours and ~40% higher over the subsequent 4–12 hours — with only minor increases in amino acid oxidation, concluding that the anabolic response to a single feeding is not capped and had been underestimated (Trommelen et al., Cell Reports Medicine 2023; 4(12):101324; n=36; note one author was a dairy-industry employee, though the company had no role in funding, data, or analysis). The honest synthesis: ~0.4 g/kg/meal still maximises the efficiency of muscle building, but the older claim that protein above that dose is "wasted" overstates the case — the excess is used more slowly, not discarded.

Number two — the macrophage threshold. The dose that saturates MPS sits immediately adjacent to the dose that activates mTORC1 in macrophages, with downstream vascular consequences. Eating more than ~25 g protein per meal, or chronically more than ~22% of total energy as protein, raises postprandial plasma leucine into the 100–300 μM window that drives macrophage mTORC1 activation.^[7] The mechanism matters: macrophages need autophagy to clear oxidised LDL from the arterial wall, and mTORC1 activation shuts that autophagy off. Macrophages unable to clear their lipid cargo become foam cells; foam cells become atherosclerotic plaques. In murine atherosclerosis models, dietary leucine content alone accounted for the entire between-group variance in macrophage mTORC1 activation and plaque burden.

Read together, the two thresholds explain why "more protein is always better" is wrong without being correctly summarised as "less is better." The dose that drives muscle hypertrophy sits right at the edge of the dose that drives vascular aging. Eating it once or twice a day around training is one regime; eating it every meal in 60–80 g servings is a different drug.

What the human data actually says

The age-dependent flip. In a 6,381-adult analysis of US national nutrition survey data, high protein intake in adults aged 50–65 was associated with 4× higher cancer mortality and 75% higher all-cause mortality — an effect driven by animal protein.^[8] Above age 65 the relationship inverts, and high protein becomes protective. This single age-dependent flip is the most consistent feature of the longevity-protein literature and frames everything else — though it came from a single national-survey analysis built on one day of self-reported diet recall, so treat the magnitude as directional rather than precise.

The population-level mortality signal actually favours protein, especially plant protein. The largest pooled analysis to date — 32 prospective cohorts, 715,128 participants, 113,039 deaths — found higher total protein intake associated with slightly lower all-cause mortality, with the clearest benefit for plant protein: each additional 3% of energy from plant protein tracked with about 5% lower all-cause mortality (Moderate, observational).^[9] This tempers any reading of "cohorts say low protein extends life": at the whole-population level the association runs the other way, and the apparent harm of animal protein concentrates in red and processed meat and in people with other lifestyle risk factors. In the Nurses' Health and Health Professionals cohorts, high animal-protein mortality risk was confined to those with at least one lifestyle risk factor, and substituting just 3% of energy from processed red meat with plant protein associated with 34% lower mortality (Moderate, observational).^[10]

The plant vs animal IGF-1 paradox. It's widely assumed animal protein raises IGF-1 more than plant protein. Tightly controlled isocaloric high-protein trials disagree: plant and animal protein produced similar increases in bioavailable IGF-1 and similar improvements in liver fat, insulin sensitivity, and adiposity.^[11] The longevity advantage of plant protein is therefore probably not about lower IGF-1 in absolute terms. The likelier drivers are differences in methionine and leucine density (next section), the surrounding food matrix (fibre, phytochemicals, lower saturated fat), and the carcinogen exposure that comes with red and processed meat specifically — not a generic "plant = less anabolic" effect.

The ceiling for healthy training adults. Intakes up to 1.6 g/kg/day support performance and recovery in active adults without metabolic detriment.^[12] The canonical quantitative anchor agrees: a meta-analysis of 49 supplementation studies (1,863 participants) found resistance-training gains in fat-free mass plateaued at about 1.62 g/kg/day (95% CI 1.03–2.20 — the confidence interval is the range in which the true value most plausibly lies, and this one is wide, reflecting real uncertainty about the exact plateau) (Strong),^[13] and the ISSN position stand puts the exercising range at 1.4–2.0 g/kg/day (Jäger et al., JISSN 2017). This is the upper bound for healthy training adults that the bodybuilding community routinely exceeds — without supporting evidence that the excess does more good than harm.

The older-adult consensus. Adequate protein in older adults protects against sarcopenia, frailty, and falls. The international expert consensus is 1.0–1.2 g/kg/day for healthy older adults, rising to 1.2–1.5 g/kg with chronic illness or convalescence and up to 2.0 g/kg during acute recovery or severe malnutrition.^[14][15] The ESPEN expert group reached the same numbers independently (≥1.0–1.2 g/kg for healthy older people, 1.2–1.5 with acute or chronic illness; Deutz et al., Clinical Nutrition 2014;33(6):929–936), and its ICU guideline notes that ~1.3 g/kg/day can be delivered progressively during critical illness (Singer et al., Clinical Nutrition 2019) (Moderate, expert consensus). The historical RDA of 0.83 g/kg is widely viewed as inadequate for skeletal preservation past midlife — and even that floor may be low: indicator-amino-acid-oxidation studies, which avoid the long adaptation of the old nitrogen-balance method, put the requirement roughly 40% higher (EAR ~0.9, RDA ~1.0–1.2 g/kg) (Humayun et al., AJCN 2007; Rafii et al.), though those breakpoints may reflect maximal anabolism rather than a true minimum (Moderate, contested method).

Adding protein with resistance training measurably rebuilds aging muscle: meta-analyses find whey plus resistance training raises appendicular muscle-mass index and grip strength in sarcopenic older adults, with whey ranked the most effective protein source across mass, grip strength, and walking speed (Cai et al. 2024, 10 RCTs; network meta-analysis, Nutrients 2024, 78 RCTs) (Strong for protein-plus-exercise; protein-alone effects are smaller).

Macronutrient ratio matters, not just total protein. In DNA-repair-deficient mice — a model of accelerated ageing — a high-protein, low-carbohydrate diet shortened lifespan by 18% in males and 36% in females, driven by mitochondrial dysfunction and systemic inflammation, while low-fat/high-carbohydrate and low-protein/high-carbohydrate diets had no lifespan-shortening effect.^[16] The implication isn't that protein is poison — it's that protein at the expense of carbohydrate, especially in a sedentary context, is not the longevity diet.

The age-dependent pivot

The single most useful frame in this literature is that protein recommendations flip somewhere in late middle age.

Anabolic resistance is the mechanism behind the late-life pivot. Older skeletal muscle is materially less responsive to a given dose of amino acids; reaching the leucine threshold for MPS requires a larger absolute amino acid load.^[17] The result: the same 20 g protein that fully stimulates MPS in a 30-year-old reaches only a fraction of maximum response in a 75-year-old. The geriatric per-meal target of 30–40 g — and the recommendation to add a pre-sleep protein feed of ~40 g to counteract the overnight catabolic window — is downstream of that physiology.^[18]

Protein source: why plant generally beats red meat, mechanistically

The clearest mechanistic case against red and processed meat in volume runs through two channels: amino acid composition (specifically methionine and leucine density) and direct carcinogenicity of preservation byproducts.

Methionine restriction and the methylation cycle

Methionine is a sulfur-containing essential amino acid that is highly concentrated in skeletal muscle meat, poultry, eggs, and dairy, and notably scarce in legumes. Across yeast, flies, rodents, and primates, restricting dietary methionine — independent of total caloric restriction — extends lifespan and improves metabolic health.^[19] The mechanism: methionine is the precursor for S-adenosylmethionine (SAM), the cell's universal methyl donor. High SAM directly stimulates mTORC1; low SAM is read as nutrient deprivation and suppresses it. Methionine restriction also induces FGF21, raising energy expenditure via brown-fat uncoupling.

The processed and red meat case

The colorectal cancer signal for processed and unprocessed red meat is independent of the mTOR story and has stood up across cohorts. Each 50 g/day of processed meat associates with a ~16–18% increase in colorectal cancer risk, and each 100 g/day of unprocessed red meat with about a 17% increase.^[20] Processed meat is IARC Group 1 (carcinogenic to humans); unprocessed red meat is Group 2A (probably carcinogenic). See Foods to limit for the wider harm signal beyond what protein per se contributes.

A more useful comparison table

Leucine and methionine content vary widely across protein sources, and that variation — not total grams — is what shifts a source's longevity-versus-hypertrophy profile.^[21]

The practical reading: lean fish, eggs, yogurt, and poultry sit in a different category from red and especially processed meat. The "animal protein is bad" blanket has always been an over-read of cohorts that mostly measured red and processed meat consumption.

Protein quality scoring, and why plant matches animal in practice

Two formal scores rate protein quality. PDCAAS — the current US/Canada regulatory standard — measures fecal digestibility and is capped at 1.0, which flatters plant proteins and undersells the best animal ones. DIAAS (FAO 2013) is the more accurate successor: it uses ileal digestibility of each individual amino acid and is uncapped. On DIAAS, several animal proteins score ≥1.0 (whole milk, egg, casein, much meat), whey and soy land in the "high quality" band (≥0.75), and many plant isolates — pea, rice, wheat, hemp, oat, fava — fall below 0.75 (Herreman et al., Food Sci Nutr 2020) (Moderate, FAO methodology plus digestibility modelling).

That scoring gap, however, mostly disappears in real outcomes once total quantity and leucine are matched. Two human training RCTs are decisive: habitual vegans and omnivores matched at ~1.6 g/kg gained similar muscle size and strength over 12 weeks of resistance training (Hevia-Larraín et al., Sports Medicine 2021), and a mycoprotein-rich vegan high-protein diet (~1.8–2.0 g/kg) matched a protein-matched omnivorous diet for myofibrillar synthesis and 10-week hypertrophy (Monteyne et al., J Nutr 2023;153(6):1680–1695) (Moderate; small, mostly young samples). Plant blends also match milk protein for acute MPS (Pinckaers et al., J Nutr 2023). The caveat is age: in older adults with anabolic resistance, an omnivorous meal can beat an isonitrogenous vegan meal for acute MPS, so plant eaters past midlife should lift their absolute dose and lean on blends. The mechanistic methionine/leucine story above explains the per-gram difference; the RCT evidence shows that with adequate quantity and blending, functional outcomes converge (Moderate).

Glycine, collagen, and the methionine buffer

The cleanest practical lever for omnivores is glycine.

Glycine is abundant in connective tissue (collagen, gelatin, skin, bone, bone broth) and largely absent from modern Western diets that rely on skeletal muscle meat. The hepatic enzyme glycine N-methyltransferase (GNMT) clears excess methionine by transferring a methyl group from SAM onto glycine, producing sarcosine. Dietary glycine therefore acts as a SAM-buffering, methionine-restriction mimetic.^[22]

In the NIH Interventions Testing Program, 8% dietary glycine extended lifespan in male and female heterogeneous mice across three independent test sites — a high bar for replication.^[23] Sarcosine, the GNMT methylation product, declines with age and independently induces autophagy in vitro and in vivo.

The practical version: if your protein backbone is meat-heavy, eat the connective tissue too — bone broth, slow-cooked stews with cartilaginous cuts, gelatin desserts, or 5–10 g of plain glycine or hydrolysed collagen daily. The collagen isn't building your tendons via mystical mechanism; the glycine is buffering your methylation cycle.

Practical protein targets

Daily total

• Sedentary midlife adult: 0.8–1.0 g/kg/day
• Active midlife adult: 1.2–1.6 g/kg/day
• Older adult (≥65): 1.0–1.5 g/kg/day — the international PROT-AGE consensus puts the floor at 1.0–1.2, rising to at least 1.2 for those who exercise.^[24]
• Hypertrophy phase, or older adult training hard, in a caloric deficit, or with chronic illness: 1.6–2.0 g/kg/day
• On a GLP-1 receptor agonist: aim for the upper end (1.6–2.2 g/kg/day) to defend against muscle loss in the drug-induced caloric deficit. See Ozempic-class drugs.

A 75 kg person at the active-midlife target lands in the 90–120 g/day band; an older adult on the geriatric target lands in the 75–115 g/day band depending on health status.

Per-meal distribution

• Target ~0.4 g/kg per meal (≈25–30 g for most adults), enough to deliver the 2.5–3.0 g leucine "muscle full" threshold.
• Distribute across 3–4 meals rather than loading into one or two — a reasonable heuristic, but not a settled fact (Weak / preliminary). It rests largely on one small crossover RCT in which even distribution (~30 g × 3) raised 24-hour MPS ~25% versus a skewed pattern (Mamerow et al., J Nutr 2014, n=8); several later RCTs and cross-sectional studies in older adults found no difference between even and skewed distribution, and no long-term trial shows distribution alone changes muscle mass (e.g., Nutrients 2022;14(21):4442; review in Nutrients 2020;12(5):1441).
• Older adults: per-meal dose rises to 30–40 g to overcome anabolic resistance.
• Add a pre-sleep ~30–40 g feed, particularly if older or in a hypertrophy phase — overnight is the longest catabolic window of the day, and pre-sleep casein raises overnight MPS (~22% in Res et al., Med Sci Sports Exerc 2012; replicated in older men by Kouw et al., J Nutr 2017), with 12 weeks of pre-sleep protein adding to muscle and strength gains in young men (Snijders et al., J Nutr 2015) (Moderate). The benefit shows up when the pre-sleep dose adds to total intake rather than just redistributing it, and the long-term muscle benefit is established in young men but not yet in older adults.
• Don't routinely exceed ~25–30 g per meal multiple times a day unless you're training around it. Eating 60–80 g of red meat in one sitting overshoots the MPS ceiling and pushes plasma leucine into the macrophage-mTORC1 window.

Source priorities

Anchor the backbone with: fish, legumes (with or without grain pairing), yogurt and kefir, eggs, poultry, soy (tofu, tempeh, edamame), nuts and seeds.

Use occasionally: lean red meat (1–3 servings/week is a reasonable upper bound; lower if family history of CRC or CVD), cheese in small amounts, whey or plant protein powder around training.

Limit aggressively: processed meats (Group 1 carcinogen — see Foods to limit for the dose-response).

Add intentionally: glycine via bone broth, gelatin, or plain glycine/collagen powder (5–10 g/day) if your animal protein intake is meat-heavy.

Protein and training

Around resistance sessions

Resistance exercise transiently activates AMPK locally (the muscle is in an energy crisis during contraction) and only swings into the mTOR-dominant, MPS-driven repair phase once exogenous amino acids arrive.^[25] The practical implication:

• 20–40 g of high-quality protein within ~2 hours of a resistance session — this is the window where the "muscle full" leucine threshold actually buys muscle, because the mechanical stimulus has primed the tissue. Whey is fast and complete; food works fine if you eat a normal protein-containing meal within the window.
• Per-session leucine ~2.5–3.0 g — corresponds to ~25 g whey or ~40 g most whole-food sources.
• The exact post-workout window is wider than the legacy "30-minute" claim implies (the anabolic window is hours, not minutes), but the closer you sit to the session the better.

Concurrent training: split the AMPK and mTOR stimuli on purpose

For people doing both endurance and resistance work, the most efficient signalling design is to separate the two physiological states rather than blur them.^[26]

• Zone 2 / longer aerobic sessions in a fasted or near-fasted state maximise AMPK activation, autophagic flux, mitochondrial biogenesis, and fat oxidation. Don't pre-load these with protein.
• Resistance training paired with post-workout protein localises mTOR activation specifically to the trained muscle, minimising systemic / vascular spillover. Don't waste the leucine bolus on cardio.
• Stacking the two on the same day, or on alternate days, both work; the principle is to avoid burying the AMPK window under continuous protein feeding.

See Resistance training for programming, Zone 2 for the aerobic side, and VO₂ max for the higher-intensity component.

BCAA supplements

Isolated branched-chain amino acid supplements (leucine, isoleucine, valine) are less effective than whole protein for muscle building. Whole protein delivers the BCAAs alongside the other essential amino acids actually required to assemble a complete protein; BCAAs alone trigger the mTOR signal without supplying the full set of building blocks, so the synthesis response is limited and can even draw on muscle breakdown to fill the gaps.^[27] The supplement industry's enthusiasm for BCAAs is older than the evidence justifying it.

Cyclical eating: TRF, protein cycling, and why blind restriction fails

Why the chronic state matters

Continuous feeding from morning to night keeps mTORC1 downstream signalling chronically elevated and AMPK chronically suppressed. The diurnal AMPK/mTOR oscillation flattens. NAD⁺ pools deplete, sirtuin activity drops, and chromatin biases toward epigenetic drift.^[28]

Time-restricted eating — confining all caloric intake to a consistent 8–12 hour window — restores that oscillation without requiring any change in total calories or protein.^[29] During the fasting window, AMPK rises sharply, autophagic flux increases, and NAD⁺ normalises. When food returns, mTOR activation is sharper and more efficient, not duller — exactly the response training-adapted tissue can use. See Fasting and time-restricted eating for the full evidence on protocols, durations, and who shouldn't fast.

Protein cycling

Once daily intake is appropriate for your life stage, an additional layer is one or two deliberately low-protein days per week — intake suppressed below ~0.8 g/kg, with calories from carbohydrate and fat. The intent is to drop systemic leucine for long enough to fully re-enable macrophage autophagy and intensify the AMPK-driven cleanup pulse, without losing skeletal muscle — resistance training maintains the muscle through brief amino acid deficits. The evidence for protein cycling as a discrete intervention is thin: unlike time-restricted eating, it has no dedicated human-outcome trials, and the rationale is extrapolated from the leucine-threshold and autophagy biology above. It's reasonable for people who tolerate it and keep a training stimulus, but it isn't established.

Why "just eat less protein" backfires

The Protein Leverage Hypothesis is the most important behavioural fact in this literature. Humans regulate protein intake to a roughly fixed daily target; if the diet is protein-dilute, total calorie intake rises until that target is met.^[30] "Eat less protein for longevity" advice in the context of an ultra-processed, protein-dilute food environment doesn't reduce protein intake; it produces hyperphagia and obesity, and the obesity does the damage. Structured restriction (TRF, protein cycling) works around this; blind restriction does not.

What's overhyped, and what's just wrong

Overhyped

• Massive protein doses every meal. Beyond ~0.4 g/kg per meal, the efficiency of muscle building falls off — the excess is still used, just more slowly (see Trommelen above) — but eaten chronically every meal it mainly fuels postprandial leucine elevation in macrophages.
• BCAA supplements for muscle building, as discussed above. Whole protein wins on every clinical endpoint.
• "Animal protein is bad" as a blanket claim. Fish, eggs, yogurt, and poultry have favourable cohort data; the harm signal lives specifically in red and processed meat.

Just wrong

• The 0.83 g/kg RDA in midlife and older adults. The international consensus is well above this; the RDA is a minimum-not-to-fall-into-overt-deficiency, not an optimum.
• "Protein damages kidneys." True only in pre-existing chronic kidney disease, where restriction to ~0.6–0.8 g/kg is still indicated. In healthy kidneys, intakes well above the RDA are tolerated long-term without nephrotoxicity (Strong): a meta-analysis of 28 RCTs found high-protein diets did not adversely change kidney function — post-intervention GFR was trivially higher (SMD 0.19) but the change in GFR did not differ from controls (SMD 0.11) — the senior author has received dairy- and beef-council funding.^[31] Don't fear protein because you read a 1990s cohort.
• "You can only absorb 30 g per meal." Conflates absorption with MPS. The body absorbs more than 30 g; what saturates around 25–40 g is muscle protein synthesis specifically. Excess is metabolised, oxidised, or — see the macrophage section — channelled into less helpful places.

Bone, weight, and frailty

Protein does not harm bone — it modestly helps (Moderate). The "dietary acid load leaches calcium from bone" idea has not held up. A National Osteoporosis Foundation systematic review found protein above the RDA is not harmful and is modestly protective of lumbar-spine bone density, with no support for the acid-load hypothesis (Shams-White/Wallace et al., AJCN 2017; NOF-funded). In older adults, pooled cohorts linked higher protein intake to about 11% fewer hip fractures (hazard ratio 0.89, 95% CI 0.84–0.94) (Groenendijk et al., Comput Struct Biotechnol J 2019).

Higher protein helps during weight loss (Strong). Higher-protein, energy-restricted diets preserve more lean mass and produce greater fat loss; a meta-analysis of 24 RCTs found they also raised resting energy expenditure by roughly 140 kcal/day (Wycherley et al., AJCN 2012), and in older adults ≥1.0 g/kg/day during weight loss retained more lean mass (Kim et al., Nutr Rev 2016). Protein also has the highest thermic effect of any macronutrient (20–30% of its energy, versus 5–10% for carbohydrate and 0–3% for fat) and is the most satiating. This is why protein matters most exactly when calories are being cut — including on a GLP-1 receptor agonist.

The frailty caveat (Weak / preliminary). Higher protein generally protects against becoming frail (e.g., Seniors-ENRICA cohort, top vs bottom tertile, about a third lower risk of incident frailty — HR 0.66; Vázquez-Fernández et al., J Cachexia Sarcopenia Muscle 2025), but in the already-frail, multimorbid old the same analysis found higher protein associated with increased mortality in the frailty-to-death transition. The reasonable reading: protein helps prevent frailty but may not rescue someone already deep in it.

Further reading

• Levine ME et al. Low Protein Intake Is Associated with a Major Reduction in IGF-1, Cancer, and Overall Mortality in the 65 and Younger but Not Older Population. Cell Metab 2014.^[32]
• Phillips SM, Chevalier S, Leidy HJ. Protein "requirements" beyond the RDA. Appl Physiol Nutr Metab 2016.^[33]
• Bauer J et al. Evidence-based recommendations for optimal dietary protein intake in older people: PROT-AGE position paper. J Am Med Dir Assoc 2013.^[34]
• Schoenfeld BJ, Aragon AA. How much protein can the body use in a single meal for muscle-building? J Int Soc Sports Nutr 2018.^[35]
• Zhang Y et al. Identification of a leucine-mediated threshold effect governing macrophage mTOR signalling and cardiovascular risk. Nature Metabolism 2024.^[36]
• Mannick JB, Lamming DW. Targeting the biology of aging with mTOR inhibitors. Nature Aging 2023.^[37]
• Schüler R, Markova M et al. Similar dietary regulation of IGF-1 and IGF-binding proteins by animal and plant protein in subjects with type 2 diabetes. Eur J Nutr 2021.^[38]
• Babygirija R, Lamming DW. The regulation of healthspan and lifespan by dietary amino acids. Transl Med Aging 2021.^[39]
• Miller RA et al. Glycine supplementation extends lifespan of male and female mice. Aging Cell 2019.^[40]
• Wolfe RR. Branched-chain amino acids and muscle protein synthesis in humans: myth or reality? J Int Soc Sports Nutr 2017.^[41]
• van Galen I et al. High protein intake causes gene-length-dependent transcriptional decline, shortens lifespan and accelerates ageing in progeroid DNA repair-deficient mice. npj Metab Health Dis 2025.^[42]
• Simpson SJ, Raubenheimer D. Protein leverage and the obesity epidemic. 2023 review.^[43]
• Regmi P, Heilbronn LK. Time-restricted eating: benefits, mechanisms, and challenges in translation. iScience 2020.^[44]
• Bouvard V et al. Carcinogenicity of consumption of red and processed meat. Lancet Oncol 2015 (IARC).^[45]
• Trommelen J et al. The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans. Cell Rep Med 2023;4(12):101324.
• Naghshi S et al. Dietary intake of total, animal, and plant proteins and risk of all cause, cardiovascular, and cancer mortality: systematic review and dose-response meta-analysis. BMJ 2020;370:m2412.^[46]
• Morton RW 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. Br J Sports Med 2018.^[47]
• Devries MC et al. Changes in kidney function do not differ between healthy adults consuming higher- compared with lower- or normal-protein diets: a systematic review and meta-analysis. J Nutr 2018.^[48]
• Hevia-Larraín V et al. High-protein plant-based diet versus a protein-matched omnivorous diet to support resistance training adaptations. Sports Med 2021.
• Deutz NEP 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.
• Bauer J 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.^[49]

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