Magnesium glycinate is created through a process called chelation, where a magnesium source, like magnesium oxide, is bound to two glycine molecules to form magnesium glycinate.
In a true magnesium glycinate supplement, this reaction is fully completed, meaning no magnesium oxide remains (this is called “fully reacted”). Based on the molecular weights of magnesium and glycine, the elemental magnesium should make up about 12–14% of the total compound.
However, if the chelation process isn’t fully completed, some unreacted magnesium oxide can remain in the final material. This means you end up with a mix of both magnesium glycinate and magnesium oxide in the one formula.
There’s also another scenario where a raw material supplier might intentionally add magnesium oxide to raise the elemental magnesium percentage. While this looks higher on the label, it’s not the same as a true fully reacted glycinate.
Hence where the best approach (if possible), is to check the label and calculate whether the elemental magnesium amount equals 12 - 14% by dividing the elemental by the total (although this can often be difficult as not all brands share the elemental & total values ... mostly just the elemental).