Guide
Magnesium glycinate vs aspartate: what's actually different
Glycinate and aspartate are both magnesium bound to an amino acid, but no human trial has compared the two directly. The closest evidence puts aspartate's absorption on par with chloride and lactate, well ahead of oxide — glycinate's own best result was a tie with oxide.
Magnesium glycinate and magnesium aspartate are both magnesium bound to an amino acid — glycine for one, aspartic acid for the other — and both are sold as general daily supplements. No human trial has ever compared the two head-to-head. The closest evidence puts aspartate's absorption on par with magnesium chloride and lactate, well ahead of magnesium oxide.
The two forms, side by side
| Magnesium glycinate | Magnesium aspartate | |
|---|---|---|
| Formula | C4H8MgN2O4 | C8H12MgN2O8 |
| Molar mass | 172.42 g/mol (PubChem CID 84645) | 288.49 g/mol, anhydrous (PubChem CID 92912) |
| Elemental magnesium by weight | ~11–14% | ~8% (varies with the salt's hydration) |
| Amino acid it's bound to | Glycine | Aspartic acid |
| Best human evidence | Tied with oxide in the one direct comparison; an amino-acid chelate beat oxide in a separate 60-day trial | Equivalent to chloride and lactate, and better than oxide, in one human bioavailability study |
| Watch out for | Lower elemental magnesium per gram than aspartate | Even lower elemental magnesium per gram; never tested against glycinate directly |
What the human evidence actually shows
A study in healthy volunteers gave four commercial magnesium preparations at about 21 mEq a day — roughly 255 mg of elemental magnesium, close to a typical supplement dose — and measured how much showed up in urine as a marker of absorption. Magnesium oxide performed poorly, at about 4% fractional absorption. Magnesium chloride, lactate and aspartate all showed significantly higher and statistically equivalent absorption to each other. Glycinate wasn't one of the four forms in that particular study.
Separately, a 2003 randomized, placebo-controlled trial gave 46 healthy adults 300 mg of elemental magnesium a day as citrate, an amino-acid chelate (the same category glycinate belongs to), or oxide for 60 days. The organic forms both outperformed oxide on 24-hour urinary magnesium excretion, and citrate came out ahead of the chelate. Aspartate wasn't tested in this trial either.
Put together, both aspartate and glycinate have separately shown better absorption than oxide in different human studies — but nobody has ever put the two in the same trial. A 2017 review of magnesium absorption research concluded that the type of magnesium salt matters less to bioavailability than is often claimed; dose and a person's existing magnesium status were identified as bigger factors than the specific salt.
What aspartate actually is
Aspartic acid is a non-essential amino acid the body makes on its own and also gets from ordinary dietary protein. Binding it to magnesium as a salt is a formulation choice, the same way glycine is used for glycinate. There's no human research directly comparing GI tolerability or any other outcome between the two amino-acid forms — the "gentler" or "better absorbed" reputation either form has is not based on a trial that tested them against each other.
Questions people ask
Is magnesium aspartate the same as magnesium glycinate?
No. They're different compounds — magnesium bound to aspartic acid versus magnesium bound to glycine — with different elemental magnesium percentages by weight. Once absorbed, the magnesium itself is chemically identical; what differs is the compound delivering it and how much of that compound the body actually takes up.
Which is better absorbed, magnesium glycinate or magnesium aspartate?
There's no trial that answers this directly. Aspartate has one human study showing absorption equivalent to chloride and lactate; glycinate has a separate study showing a tie with oxide and another showing an amino-acid chelate behind citrate. The two forms have never been tested against each other in the same trial.
Can you take magnesium glycinate and magnesium aspartate together?
There's no specific hazard in doing so, but there's no benefit either beyond taking the combined elemental total, which should stay under the 350 mg/day supplemental upper limit for most adults.
Is magnesium aspartate cheaper than magnesium glycinate?
Pricing varies by brand and isn't something a research review can settle. The fair comparison across any two forms is price per 100 mg of elemental magnesium, not price per bottle or per capsule.
Related reading
Sources
- Bioavailability of US commercial magnesium preparations In healthy volunteers given about 255 mg of elemental magnesium a day, magnesium aspartate was absorbed as well as chloride and lactate, and all three beat oxide. Glycinate wasn't tested in this particular study.
- Intestinal Absorption and Factors Influencing Bioavailability of Magnesium-An Update A 2017 review of magnesium absorption research concluded the type of magnesium salt matters less than is often claimed — the evidence for one form being reliably better absorbed than another is inconsistent.
- Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study In 46 healthy adults taking 300 mg a day for 60 days, citrate raised blood magnesium most; an amino-acid chelate did not beat it.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
