Net absorption of dietary magnesium is about 50% and can be lower with high-fiber diets, but bioavailability from plant sources can be increased by activating phytases through methods like heating, germinating, or sprouting.

“the net absorption of magnesium in the diet is only about 50% it's even lower with high fiber diets but most of the studies that have found this are studies where they feed people super high amounts of fiber which most people aren't getting even when they have a high plant Rich diet so a big reason for poor magnesium bioavailability in plant sources it be is because magnesium is bound to phate in plants and there are ways to increase bioavalability of magnesium from plants and that is by activating phases these are enzymes that break down phate so for example if you heat up oats or you cook your leafy greens or legumes or you germinate or you sprout your grain grains and seeds all of these things decrease phate levels because they activate those enzymes that are called phases”