Magnesium has widespread metabolic functions and is present in all body cells. An adult body contains about 25 g of magnesium or a little less than an ounce. About 70% of this small but vital amount is combined with calcium and phosphorus in the bone. The remaining 30% is distributed in various tissues and body fluids, where it has widespread metabolic use in all cells as a control agent. It acts as an enzyme activator for energy production and building tissue protein. It also aids in normal muscle action. The RDA standard is 350 mg/day for men and 300 mg for women. The new American recommended Dietary Reference Intakes (DRI) for magnesium, developed jointly with Health Canada, have just been issued among the National Academy of Sciences first new values report of the working DRI nutrient-energy committees.
Magnesium is relatively widespread in nature and thus in unprocessed foods. For example, large concentrations of magnesium occur in unmilled grains, but more than 80% is lost by removal of the germ and outer layers of the grain. Its main food sources include nuts, soybeans, cocoa, seafood, whole grains, dried beans and peas, and green vegetables. Most fruits, except bananas, are relatively poor sources, as are milk, meat, and fish. Thus, on the whole, diets rich in vegetables and unrefined grains are much higher in magnesium than are diets made up mostly of refined foods, meat, and dairy products.