Reason #1: Low intake of foods rich in magnesium. Magnesium is part of chlorophyll, the green pigment found in plants, so green leafy vegetables are particularly high in magnesium. The average American consumes foods that are rich in energy and poor in micronutrients such as processed foods, sugar, sodas, and even meat. This is the most significant cause of magnesium deficiency in the U.S.—not enough green vegetables in our diets. Examples of products and ingredients that contain very little magnesium: 1  Meat (very little)  Milk (very little)