There are several forms of magnesium that can be beneficial and much of the population are getting sub-optimal amounts through our diet as our soils are greatly depleted of this essential mineral. Magnesium glycinate is a highly absorbable form that does not induce loose stools like other forms (oxide, hydroxides, etc.). Magnesium threonate is also considered highly beneficial as it has been shown to pass the blood-brain barrier readily.  Foods rich in magnesium include nuts, seeds, dark green veggies, and lentils, among others.