extra water consumption.High-Potassium Foods. A study of 46,000 men conducted by Harvard University researchers found that a high potassium intake can cut the risk of kidney stones in half. Potassium helps the kidneys retain calcium, rather than sending it out into the urine. Potassium supplements are not generally necessary. Rather, a diet including regular servings of fruits, vegetables, and beans supplies plenty of potassium.Calcium. Although most stones contain calcium, the calcium in foods does not necessarily contribute to stones. Calcium supplements taken between meals may increase the risk of stones, because about 8 percent of any extra dietary calcium passes into the urine.9,11 On the other hand, calcium consumed with meals has the opposite effect, reducing the risk of stones. The reason, apparently, is that calcium binds to oxalates in foods and holds them in the digestive tract, rather than allowing them to be absorbed.Caffeine. Caffeinated beverages reduce the risk of stones. Caffeines diuretic effect causes the loss of both water and calcium, but the water loss is apparently the predominant effect. Similarly, alcoholic beverages are associated with a reduced risk of kidney stones, again presumably due to a diuretic effect. This is not a compelling reason to drink either coffee or alcohol, but their diuretic actions do present this advantage.Problem FoodsAnimal Protein. Animal proteins cause calcium to be leached from the bones and excreted in the urine where it can form stones. Diets rich in animal proteins also increase uric acid excretion. In a controlled research study, published in the American Journal of Clinical Nutrition, research subjects on a diet eliminating animal protein had less than half the calcium loss that they had on their baseline diet.12The Harvard study mentioned earlier found that even a modest increase in animal protein, from less than 50 grams to 77 grams per day, was associated with a 33 percent increased risk of stones in men.7 The same is true for women. The Nurses Health Study, a long-term study of health factors in a large group of women, revealed an even greater risk of stones from animal protein than was found in previous studies in men.9The association between animal proteins and stones probably relates both to the amount of protein they contain and to their content of the sulfur-containing amino acids. In particular, the sulfur in cystine and methionine is converted to sulfate, which tends to acidify the blood. As a part of the process of neutralizing this acid, bone is dissolved, and bone calcium ends up in the urine. Meats and eggs contain two to five times more of these sulfur-containing amino acids than are found in grains and beans.11,13Between 1958 and the late 1960s, there was a sharp increase in the incidence of kidney stones in Great Britain. During that period, there was no substantial change in the amount of calcium or oxalate-containing foods consumed. However, the consumption of vegetables decreased, and the use of poultry, fish, and red meat increased. Statistical analyses showed a strong relationship between the incidence of stones and animal protein consumption.14Sodium. Sodium increases the passage of calcium through