Which amino acids are used to make creatine?

The body synthesizes creatine from three amino acids: arginine, glycine, and methionine. Arginine and glycine combine in the first step (catalyzed by AGAT in the kidneys), and methionine provides a methyl group in the second step (catalyzed by GAMT in the liver) via S-adenosylmethionine (SAM).

Does taking creatine spare amino acids for other uses?

Yes. When you supplement with creatine, your body reduces or stops endogenous creatine synthesis, which normally consumes about 1-2g of arginine, glycine, and methionine daily. These amino acids become available for other metabolic functions including protein synthesis, nitric oxide production, and glutathione synthesis.

Is creatine synthesis a major consumer of amino acids?

Yes. Creatine synthesis is one of the largest consumers of methyl groups from SAM (S-adenosylmethionine), accounting for approximately 40% of all SAM-dependent methylation reactions in the body. It also consumes significant amounts of arginine and glycine relative to dietary intake.

Creatine and Amino Acid Metabolism: Does It Work?

Creatine Biosynthesis: A Three-Amino-Acid Story

Creatine is synthesized endogenously from three amino acid precursors: arginine, glycine, and methionine. This biosynthetic pathway is not trivial — it consumes substantial amounts of these amino acids and connects creatine metabolism to broader nitrogen balance and methylation chemistry in the body (T et al., 2011) .

~40%

of all SAM-dependent methylation reactions in the body are consumed by creatine synthesis

Wallimann et al., 2011

The Two-Step Biosynthetic Pathway

Step 1: AGAT Reaction (Kidneys)

The enzyme arginine:glycine amidinotransferase (AGAT) catalyzes the transfer of an amidino group from arginine to glycine, producing guanidinoacetate (GAA) and ornithine:

Arginine + Glycine → Guanidinoacetate (GAA) + Ornithine

This reaction occurs primarily in the kidneys and is the rate-limiting step of creatine synthesis. AGAT activity is regulated by feedback inhibition — creatine itself inhibits AGAT, reducing its own synthesis when creatine levels are adequate. This is why supplementation downregulates endogenous production.

Step 2: GAMT Reaction (Liver)

GAA is released into the bloodstream and taken up by the liver, where the enzyme guanidinoacetate N-methyltransferase (GAMT) adds a methyl group from S-adenosylmethionine (SAM) to form creatine:

GAA + SAM → Creatine + SAH (S-adenosylhomocysteine)

This methylation reaction is one of the most significant methylation events in human biochemistry, consuming approximately 40% of all labile methyl groups derived from methionine via the SAM cycle.

Impact on Arginine Metabolism

Arginine serves multiple critical functions in the body:

Creatine synthesis — donates the amidino group to glycine
Nitric oxide production — substrate for nitric oxide synthase (NOS), producing the vasodilator NO
Urea cycle — intermediate in the conversion of ammonia to urea for excretion
Protein synthesis — incorporated into proteins as one of the 20 standard amino acids
Polyamine synthesis — precursor for spermidine and spermine, important for cell growth

Creatine synthesis is a significant consumer of arginine. An adult producing approximately 1-2g of creatine daily uses a substantial fraction of available arginine. When creatine is supplemented exogenously, the reduced need for endogenous synthesis frees arginine for other functions.

This arginine-sparing effect may have practical implications:

More arginine available for nitric oxide production (potentially improving blood flow)
Reduced competition for arginine with other metabolic pathways
Possible benefit for individuals on low-protein or plant-based diets where arginine intake may be marginal

Impact on Glycine Metabolism

Glycine is often underappreciated as a metabolic amino acid. Beyond creatine synthesis, glycine is needed for:

Glutathione synthesis — glycine is a component of glutathione, the body’s primary endogenous antioxidant
Collagen synthesis — glycine comprises approximately one-third of all amino acids in collagen
Conjugation reactions — glycine conjugates bile acids and various toxins for excretion
Neurotransmission — glycine acts as an inhibitory neurotransmitter in the central nervous system
Heme synthesis — glycine contributes to the porphyrin ring of hemoglobin

Some researchers have argued that glycine is conditionally essential — the body’s capacity for glycine synthesis may be insufficient to meet the combined demands of creatine production, glutathione synthesis, and collagen turnover (RB et al., 2017) .

By supplementing creatine and reducing endogenous synthesis, more glycine becomes available for these other important functions, including antioxidant defense (glutathione) and connective tissue maintenance (collagen).

Impact on Methionine and the Methylation Cycle

The methionine impact is perhaps the most metabolically significant. Creatine synthesis is the single largest consumer of SAM-derived methyl groups in the body.

The methylation cycle operates as follows:

Methionine is activated to SAM (S-adenosylmethionine) by methionine adenosyltransferase
SAM donates a methyl group to GAA (forming creatine) or to other substrates (DNA, RNA, proteins, phospholipids)
SAH (S-adenosylhomocysteine) is formed as a byproduct
SAH is hydrolyzed to homocysteine
Homocysteine is either remethylated back to methionine (using folate or betaine as methyl donors) or converted to cysteine via the transsulfuration pathway

Because creatine synthesis consumes ~40% of SAM, supplementing creatine and reducing endogenous production has significant implications for the methylation cycle:

Less SAM consumed for creatine synthesis
Less homocysteine produced as a byproduct
More methyl groups available for DNA methylation, epigenetic regulation, and other methylation reactions

Amino Acid Sparing: Practical Benefits

The amino acid sparing effect of creatine supplementation is particularly relevant for certain populations (DG et al., 2003) :

Vegetarians and vegans — who have lower dietary creatine intake and rely more heavily on endogenous synthesis, consuming more arginine, glycine, and methionine
Older adults — who may have reduced protein intake and less efficient amino acid utilization
Athletes with high training volumes — who have increased demands for both creatine and protein synthesis
Individuals on caloric restriction — where amino acid availability may be limited

By providing exogenous creatine, supplementation effectively liberates these three amino acids for other metabolic functions, potentially improving overall nitrogen balance and methylation capacity.

Summary

Creatine synthesis from arginine, glycine, and methionine is a major consumer of amino acids and methyl groups. Supplementing with creatine reduces the demand on these precursors, freeing them for other critical functions including nitric oxide production, glutathione synthesis, collagen formation, and DNA methylation. This amino acid sparing effect adds metabolic value to creatine supplementation beyond its direct energy-buffering role.