Glycine’s not a filler in this instance. It’s used to aid absorption [1]. Mag glycinate is one of the only worthwhile forms of magnesium for supplementation, unless you’re using it as laxative. The latter being caused by gut irritation from unabsorbed magnesium.
But yes, glycine also has many of its own benefits. Including a very interesting theory regarding life extension due to its interaction with methionine. [2]
Thanks for that second link. I had read about glycine for sleep, mood, bipolar and schizophrenia (via Glenn Close family study) but not for possible life extension. It does improve my own mood with a dose of several grams per day but the best mental effect seems to be the day I stop taking it. Lower dose does not produce that, it seems to be a dynamic response. So it seems important but complicated, but that's just my anecdote.
