How many extra calories does building 1 kg of muscle take?
PREPRINT — not peer reviewed: a model, not a measurement, puts it at ~3500 kcal (3204-3710), ~40 kcal/day over 12 weeks, training not included.
Main caveat: PREPRINT — not peer reviewed. Version 1 on bioRxiv; Crossref showed no published version on 2026-10-28.
Nikolaidis, Paschalis and Margaritelis set out to calculate what nobody has measured in adults: the extra energy it takes to build 1 kg of human skeletal muscle. They built the cost from five additive parts. Stored tissue energy (177 g protein, 30 g lipid and 20 g glycogen per kg of wet muscle at gross energy values) is 5668.5 kJ (1355 kcal).
The ATP cost of assembling those molecules adds 669.5 kJ (160 kcal), giving 6338 kJ (1515 kcal). Because laying down protein in a living body is inefficient, they divide the stored protein energy by an effective protein deposition efficiency of 46% (42-52%), taken from five infant, rat and pig studies; this gives a deposition requirement of 10826 kJ (2587 kcal; 2338-2793).
Keeping the new muscle alive while it accrues over 84 days adds 2285 kJ (546 kcal), and with diet-induced thermogenesis set at 10% of the extra intake the final figure is 14570 kJ (3481 kcal) per kg, 3204-3710 kcal across the efficiency range. Gained over 12 weeks, that is about 41 kcal a day.
The authors compare it with a common 300-500 kcal/day surplus: 400 kcal/day for 84 days is 33,600 kcal, almost ten times the calculated cost of the muscle.
They do not call the usual surpluses wrong — those also pay for training, uncertainty in maintenance needs and some fat — but say a large surplus cannot be justified as the cost of the muscle itself, which fits trials in which larger surpluses added fat (REF-1088, REF-1089).
Our reading: a transparent, checkable estimate whose arithmetic holds; its weakest link is the efficiency term, borrowed from growing infants and animals, and nobody has yet measured the number.
Protocol
Design: quantitative bottom-up accounting model ("Fermi-style" decomposition), per 1 kg of wet mixed human skeletal muscle; no participants, no new data.
Composition: protein 177 g/kg (Stroh 2021), lipid 30 g/kg (Goodpaster 2004), glycogen 20 g/kg (Jensen 2011); the remainder is water and minor constituents with no retained energy. Creatine and phosphocreatine were left out as negligible (about 6.5 kJ, 1.6 kcal, per kg).
Gross energy: protein 23.5 kJ/g (5.62 kcal/g), lipid 38.9 kJ/g (9.30 kcal/g), glycogen 17.1 kJ/g (4.09 kcal/g) — the chemical energy kept in the tissue, deliberately not the dietary Atwater factor of 4 kcal/g for protein.
Synthesis cost: protein 5 ATP equivalents per amino acid at about 80 kJ/mol ATP and 110 g/mol per residue = 3.6 kJ/g (0.86 kcal/g); triacylglycerol 0.75 kJ/g (from preformed fatty acids); glycogen one ATP per glucose residue = 0.49 kJ/g.
Deposition efficiency: protein kP 46% central, 42-52% range (Roberts & Young 1988 and Towers 1997 in infants; Pullar & Webster 1977 and Coyer 1987 in rats; van Milgen 2001 in pigs; central values 42.0-52.0%); lipid 82% (mean of 73.5, 85.5 and 88.3%); glycogen 95% (from biochemical accounting, not measured).
Resting maintenance during accretion: skeletal-muscle resting metabolic rate 54.4 kJ/kg/day (13 kcal/kg/day, Wang 2010) × an average 0.5 kg of extra muscle (linear gain) × 84 days.
Diet-induced thermogenesis: 10% of the extra intake, so the biological cost is divided by 0.90.
Checks against independent data ("triangulation"): two growing-rat studies of lean-tissue accretion (Sekiguchi 2024, Obikawa 2025), the earlier human estimates summarised by Slater 2019, and a cultured-meat energy estimate (Tuomisto 2011); studies used to set the inputs were not reused as checks.
Funding and interests: the bioRxiv record states "The authors have declared no competing interest"; no funding statement appears in the full text. The authors declare that ChatGPT (OpenAI) helped with language, manuscript organisation and the presentation of calculations, and that they verified all of it.
Key Results
| Component (per kg of wet skeletal muscle) | kJ | kcal | Running total, kcal |
|---|---|---|---|
| 1. Stored tissue energy (protein 994, lipid 279, glycogen 82 kcal) | 5668.5 | 1355 | 1355 |
| 2. Biochemical synthesis cost | 669.5 | 160 | 1515 |
| 3. Physiological deposition cost (kP = 46%) | 4487.9 | 1072 | 2587 (2338 at kP 52%, 2793 at kP 42%) |
| 4. Resting maintenance during 84-day accretion | 2285 | 546 | 3133 (2884-3339) |
| 5. Diet-induced thermogenesis (10% of the extra intake) | 1457 | 348 | 3481 (3204-3710) |
Final estimate: additional metabolizable energy intake 14570 kJ/kg (3481 kcal/kg), 13410-15520 kJ/kg (3204-3710 kcal/kg) across kP 52% to 42%.
Per day: about 41 kcal/day (38-44) if the kilo is gained over 84 days; the authors say it is "too small" to prescribe as a daily add-on and excludes training sessions, repair, inflammation, connective tissue and other tissues.
Against a common surplus: 300-500 kcal/day is often advised during resistance-training phases; 400 kcal/day over 84 days = 33,600 kcal, almost ten times the 3481 kcal calculated for 1 kg of muscle.
Against other estimates: Slater 2019's human figures, 1778 and 1446 kcal/kg, sit near the model's stored-plus-synthesis value (1515), so the authors read them as a lower bound.Growing rats: 4150-4570 kcal per kg of whole-body lean tissue, higher than the model but the same order; the authors put the difference down to organs, skin, connective tissue and broader growth costs in whole-body lean tissue. Cultured meat: 5076 kcal/kg for the cultivation step, an engineered upper comparator, not a biological cost.
The arithmetic checks out: 4159.5/0.46 + 1167/0.82 + 342/0.95 = 10826 kJ; + 2285 = 13111; / 0.90 = 14568 kJ = 3481 kcal; the ends of the range reproduce at kP 52% and 42% (our recalculation).
Mechanisms
Measured (by the cited studies, not here): muscle is about 18% protein, 3% lipid and 2% glycogen by wet weight (177, 30 and 20 g/kg); the rest is mostly water with no stored energy, which is why a kilo of muscle stores only about 1355 kcal.
Authors' interpretation: the protein deposition efficiency kP is the dominant and least certain term. It is a whole-system coefficient that absorbs turnover, breakdown and resynthesis, remodelling, quality control and heat, not a molecular constant, and it has never been measured in adults gaining muscle.They suggest adult kP may, if anything, be lower than in growing infants, because adult hypertrophy is slower, localised and more remodelling-dependent — which would raise the cost.
Inference (our arithmetic): even with kP at 30%, well below the infant and animal range, the same model gives about 4760 kcal/kg, about 57 kcal a day over 12 weeks — still a small fraction of a 300-500 kcal/day surplus. The conclusion that muscle itself cannot absorb a large surplus does not hinge on the exact efficiency.
Inference: satellite cells, myonuclei, capillaries, connective tissue and mitochondria are counted only to the extent kP or the maintenance term absorbs them (the authors' own limitation); a real hypertrophy block also costs the training, repair and adaptation of other tissues, which the model leaves out on purpose.
Practical Application
How many extra calories does building 1 kg of muscle take? PREPRINT — not peer reviewed: a model, not a measurement, puts it at ~3500 kcal (3204-3710), ~40 kcal/day over 12 weeks, training not included.
Faster gain, slightly cheaper per kilo by the model (our arithmetic, not the authors'): gained in 30 days instead of 84, the upkeep term falls from 546 to about 195 kcal, so 1 kg of muscle a month comes to about 3090 kcal (2814-3320), roughly 100 kcal/day above what the training already costs (103; 94-111 across the range).A typical drug-free gain of about 1.4 kg of fat-free mass over 12 weeks (REF-1094, C+, narrative review) would be about 58 kcal/day if it were all muscle (1.4 × 3481 / 84; it is not all muscle).
Why big surpluses add mostly fat (inference from this model with the trials): in trained lifters a 15% surplus gave no group evidence for more muscle thickness or squat 1RM than 5% or maintenance, but more skinfold gain than maintenance (bench 1RM did rise more than with 5% or maintenance), and weight gain tracked skinfold gain (R² = 0.49) (REF-1088, B).In young elite athletes the counselled group ate about 621 kcal/day more than the ad libitum group (3585 vs 2964 kcal, our subtraction) for 8-12 weeks, showed no difference in lean-mass gain and gained more fat (+15% vs +3% fat mass) (REF-1089, B+).At 3481 kcal per kg, 621 kcal/day for 8-12 weeks would pay for 10-15 kg of muscle (our arithmetic) — far more than any trial shows muscle can gain, so most of it had to go somewhere else. The trials carry the evidence; the model only explains why the result is unsurprising.
The surplus pays for more than the muscle (authors' point): the model excludes the training sessions and the uncertainty of estimating maintenance. A common 300-500 kcal/day surplus is not wrong for that reason alone; it is just not the cost of the muscle.
Not from this paper; the base's own practice: gaining mass in the off-season = a small surplus steered by the trend of body weight, because large surpluses mostly add fat (SYNTH-87, with REF-1088 and REF-1089); in a build block or within weeks of an A-race, hold weight and eat for the training (SYNTH-54). This preprint supports that line and is never its sole basis.
Do not count 40 kcal a day (authors' point and practice): daily intake estimates are far less precise than 40 kcal, and the spread between people is large (REF-1127: the same 84,000 kcal surplus gave 4.3-13.3 kg of gain); use the scale trend and performance, not this number, to steer.
Limitations
PREPRINT — not peer reviewed. Version 1 on bioRxiv; Crossref showed no published version on 2026-10-28. kb-watch checks monthly for one (relation is-preprint-of).
A model, not a measurement. No human has been measured; the authors call it a "first quantitative reference estimate" and describe the experiment that would test it (controlled intake, measured energy expenditure, MRI or CT for muscle mass over a period of verified gain).
The dominant input comes from infants and growing animals. Five studies (two in infants, two in rats, one in pigs) give kP 42-52%; adult kP is unknown and the authors suggest it may be lower, which would raise the cost (at 30%, about 4760 kcal/kg by our arithmetic).
Assumed composition and time course. 177 g protein, 30 g lipid and 20 g glycogen per kg vary with muscle, fibre type, training, diet, sex and age; 84 days of linear gain and 10% diet-induced thermogenesis are reference choices, not measurements.
Wet muscle, not the scale. The figure is per kg of skeletal muscle; a gain in body weight or fat-free mass also contains water, glycogen elsewhere and other tissues, so it cannot be read straight off a scale or a body-composition report.
Rounding: the upper daily figure, 190 kJ/day, is 185 by the authors' own numbers (15520 / 84; our arithmetic); the kcal figures (38-44) are right. The rat comparator's 12.1 + 5.23 kJ/g sums to 17.3, printed as 17.4. Neither changes the estimate.
Interests and AI use. No competing interest declared; no funding statement found. ChatGPT assisted with language, organisation and presentation of the calculations, which the authors say they verified.
How this entry was checked and changed
Why this level
read from the full text (bioRxiv, CC BY 4.0). The rubric puts unvalidated modelling at C, and the preprint rule sets a preprint one step below its design with C as the floor, so C
Full text (checked 2026-10-28)
Reference composition per kg wet muscle: protein 177 g, lipid 30 g, glycogen 20 g; total stored tissue energy 5668.5 kJ/kg (1355 kcal/kg) (full text)
Stored tissue energy plus biochemical synthesis cost = 6338 kJ/kg (1515 kcal/kg) (full text)
Protein deposition efficiency: 46% as a pragmatic central value with 42% to 52% as the primary sensitivity range, from five studies; no direct data in adult humans (full text)
Physiological deposition requirement 10826 kJ/kg (2587 kcal/kg) at kP 0.46; 9780 kJ/kg (2338 kcal/kg) at kP = 52% and 11690 kJ/kg (2793 kcal/kg) at kP = 42% (full text)
Resting maintenance = 54.4 kJ/kg/day x 0.5 kg x 84 days = 2285 kJ/kg (546 kcal/kg) (full text)
Diet-induced thermogenesis approximated as 10% of additional metabolizable energy intake: 1457 kJ/kg (348 kcal/kg) (full text)
Final additional metabolizable energy intake 13410 to 15520 kJ/kg (3204 to 3710 kcal/kg), central 14570 kJ/kg (3481 kcal/kg) (full text)
Over 84 days the central estimate corresponds to approximately 170 kJ/day (41 kcal/day), 38 to 44 kcal/day across the range (full text)
A 400 kcal/day surplus over 84 days corresponds to 33,600 kcal, almost tenfold the calculated tissue-specific requirement (full text)
Slater et al. (2019) human estimates 1778 and 1446 kcal/kg; growing rats 4150 to 4570 kcal/kg lean tissue (full text)
The authors have declared no competing interest; ChatGPT (OpenAI) was used for language refinement, manuscript organization and presentation of calculations (full text)