How Much Protein to Build Muscle: g/kg Targets, Timing & Distribution (Morton 2018)

Ask ten gym-goers how much protein they need to build muscle and you'll get ten different answers, ranging from "1 gram per pound of bodyweight" to "as much as you can eat." The fitness industry has a long history of inflating protein recommendations — supplement companies have a financial interest in doing so.

The science is more nuanced, and the optimal intake is lower than the gym-floor consensus suggests. This guide walks through the key meta-analysis (Morton 2018), the g/kg targets that emerge from it, how distribution and per-meal dose matter more than timing, leucine and protein quality, and what changes for older adults, plant-based eaters, and people in a fat-loss phase.

Why Protein Is the First Macro to Set

Protein has three properties that make it the macro to lock in first:

1. It's required for muscle protein synthesis. Carbs and fat can be substituted for each other within wide limits without affecting body composition; protein cannot. Below threshold intake, no amount of training fully compensates.
2. It's the most satiating macro. Per calorie, protein produces stronger and longer-lasting satiety than carbs or fat — particularly important during a fat-loss phase.
3. It has the highest thermic effect of food. Roughly 20–30 % of protein calories are spent on digestion and metabolism, vs 5–10 % for carbs and 0–3 % for fat. A high-protein diet effectively reduces net calorie absorption.

For these reasons, evidence-based macro frameworks (see our macro calculation guide) treat protein as the first floor to set, with carbs and fat absorbing the remaining calories.

The Best Study: Morton et al. (2018)

The most comprehensive analysis of protein and muscle growth is the meta-analysis by Morton, Murphy, McKellar et al., published in the British Journal of Sports Medicine in 2018. It pooled data from 49 randomised controlled trials with 1,863 participants, making it the most statistically powerful investigation of this question to date.

Key findings

• Protein supplementation significantly increased fat-free mass gains from resistance training compared to lower intake (mean effect: +0.30 kg additional FFM, +9 % strength gain).
• The benefit plateaued at approximately 1.62 g per kg of bodyweight per day.
• Above this level, additional protein produced no further benefit for lean mass or strength gains.
• The upper 95 % confidence interval extended to 2.2 g/kg — suggesting some individuals (lean, older, in a deficit) may need slightly more.
• Older participants showed weaker effects than younger participants (anabolic resistance).
• Trained participants showed weaker effects than untrained participants — meaning the absolute benefit of additional protein decreases as training experience increases.

For an 80 kg lifter, the practical takeaway: 130 g of protein per day captures almost all the available muscle-building benefit. Going to 175 g (≈2.2 g/kg) is the upper bound where benefit might still occur. Above that, you're spending grocery money on no additional muscle.

Protein Targets by Goal

The optimal intake shifts based on training context, body composition, and life phase. Synthesised from Morton 2018, the ISSN Position Stand (Jäger 2017), and Helms 2014:

Profile	Recommended Intake	Source
General fitness, light training	1.2–1.6 g/kg/day	ISSN 2017
Build muscle (caloric surplus)	1.6–2.2 g/kg/day	Morton 2018, ISSN
Lose fat while preserving muscle (deficit)	2.0–2.4 g/kg/day	Helms 2014, ISSN
Lean natural bodybuilder, contest prep	2.3–3.1 g/kg of fat-free mass	Helms 2014
Endurance athlete, high training load	1.4–1.8 g/kg/day	Thomas 2016
Older adults (65+), healthy	1.0–1.2 g/kg/day	PROT-AGE 2013
Older adults, active or in illness recovery	1.2–1.5 g/kg/day	PROT-AGE 2013

Why higher in a deficit?

Caloric restriction shifts the muscle protein balance equation: synthesis remains driven by training and protein intake, but breakdown rises. Higher protein partially compensates by stimulating synthesis more strongly and by increasing satiety, helping adherence to the calorie target. Lean individuals in extended deficits are at the highest risk of muscle loss, which is why Helms recommends the upper bound and switching to a per-kg-of-LBM basis.

For more on the deficit math, see our optimal caloric deficit guide.

Why lower for older adults — but with bigger meals

The PROT-AGE recommendation looks counterintuitive at first — older adults need more, but the table shows lower g/kg than for resistance trainees. Two reasons: (1) the studies focus on healthy ageing, not muscle gain, and (2) older muscles are less responsive per-meal, so the per-meal dose matters more than the daily total. Older adults benefit from larger individual meals (35–40 g protein) rather than just more total protein.

Per-Meal Distribution and the Leucine Threshold

Beyond the daily total, how protein is distributed across meals affects 24-hour muscle protein synthesis. The optimal pattern is roughly equal protein doses at 3–5 meals, each large enough to maximally stimulate synthesis.

Areta et al. (2013) compared three patterns of an identical 80 g daily protein dose: (a) 8 × 10 g every 1.5 hours, (b) 4 × 20 g every 3 hours, (c) 2 × 40 g every 6 hours. The 4 × 20 g pattern produced the highest 12-hour muscle protein synthesis. Both extremes — many tiny doses and few large doses — underperformed.

The mechanism: each meal triggers a roughly 3-hour synthesis pulse, but the pulse only fires if a leucine threshold is met (~2.5–3.0 g leucine, equivalent to ~25–35 g of high-quality protein). Below the threshold, protein is largely shunted to non-muscle uses; above it, the pulse fires and saturates.

Practical per-meal targets

• Younger adults (under 50): ~0.4 g/kg per meal (e.g. 32 g for an 80 kg lifter)
• Older adults (65+): ~0.6 g/kg per meal (e.g. 42 g for a 70 kg adult, to overcome anabolic resistance)

Common per-meal options that hit the threshold:

• 130 g chicken breast (≈40 g protein, ≈3.3 g leucine)
• 4 large eggs + 100 g Greek yoghurt (≈35 g protein)
• 150 g salmon (≈35 g protein)
• 200 g cottage cheese (≈25 g protein) + 1 scoop whey (≈25 g)
• 35 g whey protein isolate (≈30 g protein, ≈3.0 g leucine — the gold standard for trigger)

Protein Timing — The Anabolic Window Reconsidered

The "anabolic window" — the idea that protein must be consumed within 30 minutes after training to maximise muscle gain — has been substantially walked back by the research. Schoenfeld, Aragon, and Krieger's 2013 meta-analysis found that total daily protein intake is the dominant variable; timing provides at most a marginal additional benefit when total intake is matched.

Aragon & Schoenfeld (2013) reframed the window as several hours wide on either side of training, not 30 minutes. A pre-workout meal containing 30–40 g of protein consumed 1–2 hours before training is still releasing amino acids during and after the session. A post-workout meal within 2 hours is functionally equivalent.

The practical implication: don't rush home from the gym for a shake. Eat normally before training, eat normally after, hit your daily total. The marginal "perfect timing" gain is invisible compared to the 50 % miss most people have on their daily g/kg.

Protein Quality: Animal vs Plant

Not all protein is metabolically equal. Quality is determined by:

• Amino acid completeness — does it contain all 9 essential amino acids in sufficient amounts?
• Leucine content — leucine is the dominant trigger for muscle protein synthesis
• Digestibility — DIAAS (Digestible Indispensable Amino Acid Score) is the modern measure

Animal proteins (whey, casein, eggs, beef, chicken, fish) are complete and high in leucine. Most plant proteins are incomplete (lower in one or more essential amino acids — typically lysine, methionine, or tryptophan) and lower in leucine per gram.

Source	Leucine per 25 g protein	Quality (DIAAS)
Whey protein isolate	2.5–3.0 g	1.09 (excellent)
Whole egg	2.1 g	1.13 (excellent)
Chicken breast	2.0 g	1.08 (excellent)
Cow's milk	2.4 g	1.14 (excellent)
Soy protein isolate	2.0 g	0.91 (very good)
Pea protein isolate	2.1 g	0.82 (good)
Wheat protein	1.7 g	0.40 (low)
Rice protein	1.9 g	0.59 (moderate)

Practical implications for plant-based eaters

Vegan and vegetarian lifters can absolutely build muscle, with two adjustments:

1. Higher total intake. Aim for the upper end of the range (2.0–2.4 g/kg) to compensate for lower per-gram leucine and DIAAS.
2. Combine sources. Soy + grains, pea + rice, legumes + grains: complementary amino acid profiles approximate animal completeness.

Hevia-Larraín et al. (2021) compared vegan and omnivorous resistance trainees over 12 weeks at matched protein intake (~1.6 g/kg). Muscle growth was equivalent. The bigger challenge for plant-based lifters is hitting total grams in the first place — vegetable proteins are calorically dense, and getting 150–180 g/day from beans and tofu requires deliberate planning.

Is High Protein Bad for the Kidneys?

The "high protein damages your kidneys" claim is a holdover from clinical recommendations for people with pre-existing chronic kidney disease (CKD), where protein restriction can slow disease progression. The evidence for healthy adults is the opposite.

Devries et al. (2018) meta-analysis of 28 trials (1,358 participants) found no adverse effects of high protein intake — up to 2.8 g/kg/day in the trials studied — on kidney function in healthy adults. Glomerular filtration rate (the primary kidney function marker) was unchanged.

People with diagnosed kidney disease should follow protein recommendations from their healthcare provider, since their needs differ from the general population. For everyone else with normal kidney function, the upper limit found in the research literature has not been associated with kidney harm.

Do You Need Whey Protein Supplements?

No. Whey protein is convenience, not magic. If you can hit your daily g/kg target through whole foods (chicken, eggs, dairy, fish, legumes, tofu), supplements add nothing.

Where supplements earn their place:

• Convenience post-workout when whole-food prep isn't practical
• Travel when high-quality protein sources are scarce
• Older adults with reduced appetite who struggle to hit per-meal protein doses through food
• High-volume athletes needing 200+ g/day, where additional whole-food meals would create digestive load

Whey vs casein: whey digests fast (peak amino acid availability ~30–60 min) and casein slow (sustained release over 4+ hours). For body composition, the practical difference is small. Whey is the default choice for around-workout use; casein is sometimes used pre-bed to extend overnight amino acid availability — a marginal benefit at best when daily totals are met.

Limitations and Honest Caveats

1. Bodyweight as a denominator is imperfect. The Morton 2018 g/kg target uses total bodyweight. For people with very high body fat, this overestimates true need (fat tissue isn't metabolically protein-demanding in the same way as muscle). Lean individuals or natural bodybuilders should switch to grams per kg of lean body mass per Helms 2014.

2. Trained vs untrained matters. The Morton 2018 effect was substantially weaker in trained subjects than untrained. Newer trainees benefit more from any protein increase; advanced lifters near their natural FFMI ceiling see diminishing returns even when nominal targets are met.

3. Total daily intake matters more than perfection. Worry about hitting 1.6–2.2 g/kg every day. Stop worrying about whether your post-workout shake was 30 minutes or 2 hours after your session. The first variable explains 80 % of the outcome; the second explains a few percent.

4. Quality of training is the upstream variable. No protein intake compensates for inadequate training stimulus. Progressive overload — gradually increasing weight, volume, or intensity over weeks and months — is the upstream cause of muscle growth. Protein supports it; it does not substitute for it.

Sources

1. Morton, R.W., Murphy, K.T., McKellar, S.R., et al. (2018). 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. British Journal of Sports Medicine, 52(6), 376–384. DOI: 10.1136/bjsports-2017-097608
2. Jäger, R., Kerksick, C.M., Campbell, B.I., et al. (2017). International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition, 14, 20. DOI: 10.1186/s12970-017-0177-8
3. Helms, E.R., Aragon, A.A., & Fitschen, P.J. (2014). Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition, 11, 20. DOI: 10.1186/1550-2783-11-20
4. Schoenfeld, B.J., Aragon, A.A., & Krieger, J.W. (2013). The effect of protein timing on muscle strength and hypertrophy: a meta-analysis. Journal of the International Society of Sports Nutrition, 10, 53. DOI: 10.1186/1550-2783-10-53
5. Aragon, A.A., & Schoenfeld, B.J. (2013). Nutrient timing revisited: is there a post-exercise anabolic window? Journal of the International Society of Sports Nutrition, 10, 5. DOI: 10.1186/1550-2783-10-5
6. Areta, J.L., Burke, L.M., Ross, M.L., et al. (2013). Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis. The Journal of Physiology, 591(9), 2319–2331. DOI: 10.1113/jphysiol.2012.244897
7. Bauer, J., Biolo, G., Cederholm, T., et al. (2013). Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. Journal of the American Medical Directors Association, 14(8), 542–559. DOI: 10.1016/j.jamda.2013.05.021
8. Devries, M.C., Sithamparapillai, A., Brimble, K.S., Banfield, L., Morton, R.W., & Phillips, S.M. (2018). 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. Journal of Nutrition, 148(11), 1760–1775. DOI: 10.1093/jn/nxy197
9. Hevia-Larraín, V., Gualano, B., Longobardi, I., et al. (2021). High-protein plant-based diet versus a protein-matched omnivorous diet to support resistance training adaptations: a comparison between habitual vegans and omnivores. Sports Medicine, 51(6), 1317–1330. DOI: 10.1007/s40279-021-01434-9