So there are 2 parts to this question.
When we say pure magnesium glycinate ... this is referring to the quality of the magnesium glycinate itself.
Unfortunately, it is common for brands to mix it - or have it 'buffered' - with other forms of magnesium (like magnesium oxide) ... which are often lower quality & poorly absorbed. A way to lower cost.
And in most cases, this is not disclosed on the label.
We guarantee our magnesium glycinate to be pure (only magnesium glycinate), and not 'diluted' with any other lower quality forms of magnesium.
The second part about leucine ...
All supplements on the market include excipients / additives in their formulation to support the manufacturing process (quality brands will use as little as possible).
Excipients in our supplements are required to prevent the powder from sticking or clumping together, during the encapsulation process.
And we include a small amount of leucine in our magnesium glycinate formula (leucine is a natural amino acid & acts as the perfect, clean label flowing agent).