Most explanations of creatine begin with what it does and work backwards to what it is. That order hides the most useful fact about it, which is a number: a normal muscle already holds about 120 mmol of creatine per kilogram of dry mass, and the ceiling is about 160. Everything creatine supplementation can do has to happen inside that gap. This is research journalism and contains no usage guidance, per our editorial standards.
The molecule, and where the body gets it
Creatine is a guanidino compound — a member of the phosphagen family — found naturally in red meat and seafood. The body does not depend on food for it. Synthesis takes place primarily in the liver and kidneys: arginine and glycine are joined by the enzyme arginine:glycine amidinotransferase to form guanidinoacetate, which is then methylated by guanidinoacetate N-methyltransferase using S-adenosyl methionine (Kreider et al., ISSN position stand, J Int Soc Sports Nutr 2017, PMID 28615996).
Once made or eaten, it distributes unevenly:
| Where it is | Share of the body pool |
|---|---|
| Skeletal muscle | ~95% |
| Brain and testes | ~5% |
Inside muscle, about two thirds is phosphocreatine and the rest is free creatine. Phosphocreatine is the functional form: it holds a phosphate group that can be handed to ADP to remake ATP faster than any other pathway in the cell, which is what makes it useful for efforts measured in seconds rather than minutes.
The pool turns over. About 1 to 2% of intramuscular creatine degrades to creatinine each day and leaves in the urine, so the body replaces roughly 1 to 3 g a day depending on how much muscle there is to supply. About half of that replacement comes from food and the rest is synthesised.
Food is a weak lever by comparison. A pound of uncooked beef or salmon carries about 1 to 2 g. In the 1992 study that first established that oral creatine raises muscle content, the authors put the comparison plainly: a single 5 g dose corresponds to the creatine content of about 1.1 kg of fresh, uncooked steak (Harris, Söderlund & Hultman, Clin Sci 1992, PMID 1327657; doi:10.1042/cs0830367).
The ceiling, and the three things it predicts
Here is the arithmetic that does the work on this page. Typical store ~120 mmol/kg dry mass. Ceiling ~160. Reported vegetarian stores 90 to 110.
| Starting point | Headroom to the 160 ceiling |
|---|---|
| Vegetarian, 90 mmol/kg | ~78% |
| Vegetarian, 110 mmol/kg | ~45% |
| Typical omnivore, 120 mmol/kg | ~33% |
| Someone already near 150 | ~7% |
A store with a hard ceiling, approached from different distances by different people, makes three predictions before a single outcome trial is opened. Each one is checkable.
Prediction one: people who start lower should gain more. The 1992 study reported exactly that — the rise in total creatine "was greatest in subjects with a low initial total creatine content", and in some of them the increase reached 50%.
Prediction two: vegetarians should separate from omnivores. In 2017 a group in São Paulo gave 0.3 g/kg/day for seven days to 64 people — children, omnivorous adults, vegetarian adults and elderly adults — and measured phosphocreatine directly by magnetic resonance spectroscopy. Muscle phosphocreatine rose significantly in vegetarians, children and the elderly. In omnivorous adults it did not reach statistical significance (p = 0.3348) (Solis et al., J Appl Physiol 2017, PMID 28572496; doi:10.1152/japplphysiol.00248.2017).
Prediction three: a tissue that does not take up creatine should not show an effect. The same study measured brain phosphocreatine in the same people on the same protocol. Muscle rose 10.3% to 27.6% depending on the group. Brain moved -0.7% to +3.9%, and was not significantly changed in any group. The authors' own summary is that brain phosphocreatine "was shown to be unresponsive overall".
That third result is the one worth holding onto, because it constrains a whole category of claim. The mechanism usually offered for creatine and cognition is that supplementation raises brain energy reserves. The study that measured whether it does, in both tissues at once, found the muscle effect and not the brain effect. We grade the cognitive evidence separately from the muscle evidence on our page about what creatine has actually been shown to do, and the two grades are not the same.
What this means for reading any creatine claim
A ceiling of roughly a third above a typical starting point is a real, useful effect and a bounded one. It sets the shape of what the literature can find: consistent small-to-moderate benefits in short, repeated, high-intensity work; larger effects in people who began further from the ceiling; and nothing at all in a tissue the compound does not load into.
It also explains the two most common disappointments. Someone whose diet is already rich in red meat and seafood has less room to fill. And no protocol can push past 160 — which is why the fastest way to fill the store does not produce a bigger store, only an earlier one. Our page on what the loading trials actually measured traces that specific point through the two biopsy studies it came from, and the dose figures in circulation turn out to disagree with each other for reasons this ceiling explains.
The limits of this page
The ISSN position stand is the source for the store and turnover figures here, and it should be read with its authorship in view: it is written by researchers who disclose scientific advisory roles with creatine manufacturers, industry-sponsored research and consultancy for supplement companies. The underlying physiology it summarises is old, independently replicated and not in dispute; the interpretive framing around it comes from people with commercial ties, and readers are entitled to know that.
The 2017 spectroscopy study is a single study of 64 people. Its muscle findings agree with the 1992 biopsy work; its brain finding is the strongest direct measurement available but has not been repeated at scale.
Nothing on this page is guidance about using creatine. It reports what has been measured, by whom, and when. Decisions about supplementation belong with a clinician.
Sources
- Kreider RB, Kalman DS, Antonio J, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. J Int Soc Sports Nutr 2017;14:18 — PMID 28615996 · PMC5469049
- Harris RC, Söderlund K, Hultman E. Elevation of creatine in resting and exercised muscle of normal subjects by creatine supplementation. Clin Sci 1992;83(3):367–74 — PMID 1327657 · doi:10.1042/cs0830367
- Solis MY, Artioli GG, Otaduy MCG, et al. Effect of age, diet, and tissue type on PCr response to creatine supplementation. J Appl Physiol 2017;123(2):407–14 — PMID 28572496 · doi:10.1152/japplphysiol.00248.2017
- Hultman E, Söderlund K, Timmons JA, et al. Muscle creatine loading in men. J Appl Physiol 1996;81(1):232–7 — PMID 8828669 · doi:10.1152/jappl.1996.81.1.232
All sources retrieved 2026-09-16. Digital object identifiers verified by content negotiation on the same date.