Magnesium gluconate is used to treat low blood magnesium. Low blood magnesium is caused by gastrointestinal disorders, prolonged vomiting or diarrhea, kidney disease, or certain other conditions. Certain drugs lower magnesium levels as well. balanced diet usually provides enough magnesium. Sometimes supplements are necessary because of illness or medication use. Magnesium is found in a variety of foods, including green leafy vegetables, nuts, peas, beans, and cereal grains with the outer layers intact. A high-fat diet may decrease the amount of magnesium you absorb from your diet. Over- cooking food also may decrease the amount of magnesium you absorb from your food. Follow the diet recommended by your doctor or dietitian. Ask if you are not sure you are getting enough vitamins and minerals.