Kidney Stones - Prevention

Protein Restriction. Protein increases uric acid, calcium, and oxalates in the urine and reduces citrate. Diets high in protein, particularly meat protein, have been consistently associated with kidney stones. (Meat protein has a higher sulfur content and generates more acid than vegetable protein.) A 2002 trial of those following a high-protein, low-carbohydrate diet, popularized in such weight-loss regimens as the Atkins diet, for example, found dramatically increased levels of urinary uric acid and calcium after just several weeks. These effects put patients at higher risk not just of kidney stones but possibly of osteoporosis as well. According to Swiss studies, about a third of people at risk for calcium stones may have a sensitivity to meat proteins that cause mild hyperoxaluria.

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Whether restricting meat protein alone has any protective value without restricting sodium as well is unknown. Most studies to date have found no difference in stone development between people with low and normal meat protein diets over four years. A 2000 study reported that only dramatic reductions in meat protein had any preventive effect against stone recurrence.

Although the precise role of dietary protein in kidney stones needs further elucidation, it is reasonable for everyone to consume meat protein in moderation. People with struvite stones, who need to reduce phosphates in their diets, should also cut down on proteins.

Role of Calcium

Calcium from Foods. Dietary calcium recommendations for kidney stone prevention need to be determined on an individual basis. A doctor will suggest calcium guidelines based on a patient?s age, gender, body size, and type of stone. Most studies indicate that dietary calcium (found in milk, yogurt, and cheese) protects against many types of calcium oxalate stones. Large studies of both men and women found that those with the highest intake of calcium from foods had a much lower risk for stones than those who had little calcium in their diets. A diet containing a normal amount of calcium, but reduced amounts of animal protein and salt, may protect against stones better than a low-calcium regimen. However, calcium metabolism changes as people age. Some studies suggest that a high calcium intake protects against kidney stones in men younger than age 60, but not in older men.

Dietary calcium may actually bind the oxalate in foods, preventing it from being absorbed into the blood and excreted into the urine. In a normal healthy diet, dairy products supply almost 80% of the daily calcium requirement. For people have calcium stones associated with resorption (the breakdown of bone that releases calcium into the bloodstream), limiting calcium intake could cause further bone loss.