Role of diet in kidney stones

A low-calcium diet is usually recommended to prevent recurrent kidney stones in patients. Recently, the need for a low-calcium diet has been questioned as the efficacy of such a diet is lacking and greater importance has been placed on reducing the intake of animal protein and salt. Kidney stones can form anywhere in the urinary system. They develop when certain chemicals in the urine form crystals that sticks together. The crystals grow into a stone, which can range in size from a grain of sand to a golf ball. Small stones can pass through the urinary system without causing too much problems. However, larger stones can block the flow of urine or irritate the lining of the urinary tract. Most stones (70 to 80 percent) contain calcium oxalate crystals. A five-year study was carried out at the University of Parma, Italy by comparing the effect of two diets in 120 men with recurrent kidney stones. Sixty men were assigned to a diet containing a normal amount of calcium (30 mmol per day) but reduced amounts of animal protein (52 g per day) and salt (50 mmol of sodium chloride per day); the other 60 men were assigned to the traditional low-calcium diet, which contained 10 mmol of calcium per day. 12 of the 60 men on the normal-calcium, low-animal-protein, low-salt diet and 23 of the 60 men on the low-calcium diet had relapses or recurrences. The results show that men on a low-calcium diet were twice as likely to develop kidney stones than those getting a normal amount of calcium. The best way of preventing the painful stones seems to lie with the intake of less animal protein and salt. Men on a diet low in salt and animal protein, but who consumed normal amounts of calcium, had half the chance of developing stones as men on a low-calcium diet. This type of diet will be of greatest value when it is started early in the course of the disease. This study provides a clear answer to the question of the relative efficacy of these conventional approaches.