Food. Magnesium is widely distributed in plant and animal foods and in beverages. Green leafy vegetables, such as spinach, legumes, nuts, seeds, and whole grains, are good sources [ 1, 3 ]. In general, foods containing dietary fiber provide magnesium.Magnesium is also added to some breakfast cereals and other fortified foods.Some types of food processing, such as refining grains in ways that remove the nutrient-rich germ and bran, lower magnesium content substantially [ 1 ].Selected food sources of magnesium are listed in Table 2.agnesium is also added to some breakfast cereals and other fortified foods. Some types of food processing, such as refining grains in ways that remove the nutrient-rich germ and bran, lower magnesium content substantially [ 1 ]. Selected food sources of magnesium are listed in Table 2.