Magnesium bisglycinate: 300 mg of salt
isn't 300 mg of magnesium

A bisglycinate isn't a powder,
it's a molecule with a shape

Magnesium doesn't exist as such in a capsule. As a metal, it would catch fire. What goes into a capsule is always a salt or a complex, meaning magnesium bound to something else, and that something else has weight too.

In bisglycinate, that something else is glycine. Not mixed with the magnesium, but chemically bound to it, at two points. That's the difference between a mixture and a chelate: in a mixture the two components sit side by side, in a chelate one grips the other.

The coordination chemistry literature describes exactly how. Glycine behaves as a bidentate ligand, meaning it grips at two points: through the nitrogen atom of the amino group and through one of the oxygens of the acid group. Those two bonds close a ring of five atoms, described in the 2020 paper in Molecules as “a five-membered ring structure, very stable and entropically favoured”.

The magnesium ion has six binding sites, arranged octahedrally, like the corners of an octahedron around it. If one glycine takes two sites, two glycines take four. That leaves two, which are usually filled by water molecules. The prefix bis in bisglycinate isn't marketing: it counts the two glycines.

Why glycine
and not another amino acid

Glycine is the smallest amino acid. Instead of a side chain it has a single hydrogen atom, and in any list of amino acids sorted by size it always comes first. What makes it small also makes it suited to this job: there's nothing bulky to get in the way of the bond.

The second reason is geometry. The distance between the nitrogen of the amino group and the oxygen of the acid group is exactly right for the ring that closes to have five atoms, the most stable size for rings of this kind. Aspartate and glutamate form similar rings, but glycine does it with the least material.

And the third reason is trivial but matters all the same: glycine is cheap, it's an amino acid the body makes on its own, and it doesn't taste bitter, which makes life simpler for anyone putting the powder into a capsule.

The arithmetic on the label,
in two divisions

The international commission that sets atomic weights gives magnesium the interval 24.304 to 24.307, with the abridged value 24.305. The commission also explains why it's an interval and not a fixed number: “the atomic weight of magnesium is not a constant of nature, but depends on the source of the material”.

The magnesium bisglycinate molecule weighs 172.42 g per mole. The figure appears identically in the data sheet of a pharmaceutical raw material producer, and it comes out the same if you calculate it yourself: 24.305 for magnesium plus twice 74.06 for the two glycinate residues.

From here on it's a division. 24.305 divided by 172.42 gives 0.141, or 14.1%. Multiply by what it says on your box and you have the amount of magnesium. For 100 mg of salt, roughly 14 mg of magnesium.

What makes this figure useful isn't its precision, but the fact that it shows you which question to ask. A well made label shows both numbers, separately. A hasty one shows only the weight of the salt, which sounds better.

The same figure, 100, in three statements that say different things. The third is the only one that leaves you nothing to work out.

What happens to the chelate
after you swallow it

This is where the part marketing skips begins, because the answer isn't as tidy as the molecule.

Magnesium is absorbed mainly in the small intestine, with some in the colon too, and it has two routes for this: a passive one, between cells, and an active one, through dedicated channels and transporters. The 2021 review in Nutrients names both and describes them as separate systems, not as variants of the same thing.

The health professional fact sheet from the US Office of Dietary Supplements gives the general figure: “approximately 30% to 40% of the dietary magnesium consumed is typically absorbed by the body”. And it gives the principle in a single sentence: “forms of magnesium that dissolve well in liquid are more completely absorbed in the gut than less soluble forms”.

A detail from physics explains why solubility matters so much. A magnesium ion never travels bare. It has a strong affinity for water of hydration, and its hydrated radius is, according to the same Molecules paper, about 400 times larger than the radius of the dehydrated ion. What passes through a wall isn't the atom, it's the atom plus its coat of water.

What isn't known for certain, and it's worth saying plainly, is whether the chelate stays whole until it reaches the intestinal wall or comes apart on the way. Both versions get cited. A measurement showing directly, in people, how much of the swallowed glycinate reaches the cell intact isn't one I can show you.

There's also a common sense rule the body applies on its own: magnesium absorption is inversely proportional to how much you already have. The emptier the reservoir, the more of what you swallow gets in. A bigger dose doesn't translate linearly into more magnesium absorbed.

This result doesn't say bisglycinate is a weak form. It says the ranking everyone repeats didn't come out the same way in a laboratory model, and that a single test neither overturns nor confirms anything on its own. We include it because it's the most recent measurement across several products at once, and because its direction is uncomfortable. If you're interested in the comparison between forms as such, we've written about it separately, in the article on magnesium glycinate, citrate or oxide.

Where the body's magnesium sits,
and why a blood test says little

An adult has between 20 and 28 grams of magnesium in total. Over 99% of it is inside cells: 50 to 65% in bone, 34 to 39% in muscle, soft tissue and organs. Less than 1 to 2% remains in the blood and the fluids outside the cells.

That's why magnesium is a cofactor in more than 300 enzyme systems, as the official fact sheet says, yet hard to assess from a single sample. The part that's easiest to measure is precisely the smallest part.

For an article about labels, the practical conclusion is short: the amount you swallow is a number you can check, and what reaches the cell isn't. All the more reason to know exactly what you've swallowed.

What our label says
on the magnesium line

In our range, magnesium is in Full-calm, the evening capsules. A serving of two capsules contains 300 mg of Magnesium Bisglycinate, meaning magnesium bound to two glycine molecules, with no magnesium oxide in the formula, and the amount of elemental magnesium is listed separately on the label. The same serving contains 400 mg of L-theanine, 200 mg of GABA, 200 mg of lemon balm extract and 2 mg of melatonin, 1,102 mg of actives in total, each with its own dose written out, with no proprietary blends. Made in the European Union, under good manufacturing practice, with a certificate of analysis for every batch.

Melatonin contributes to the reduction of time taken to fall asleep. The beneficial effect is obtained by consuming at least 1 mg of melatonin close to bedtime.

Take two capsules with a glass of water, 30 to 60 minutes before bed. From this article, the only thing to remember about our label is the form: bisglycinate, so magnesium held by two glycines, so two different figures on the same line, and both listed. We've written at length about the rest of the formula in the Full-calm guide.

One practical tip that has nothing to do with us: magnesium isn't an active you take as needed, but one that builds up through repeated intake, over weeks. And if you take several supplements on the same day, the timing matters more than you'd think, and we've pieced it together in which supplements shouldn't be taken together.

Frequently asked
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