Kidney stones are hard crystals formed in the kidneys. The stones usually produce no symptoms until they pass through the ureter, the muscular tube that connects the kidneys and the bladder. When stones pass, they can produce severe pain, nausea, vomiting and other symptoms. There are a few types of kidney stones. Calcium phosphate stones form from calcium and phosphorus when the urine is relatively alkaline. Foods that increase calcium excretion into the urine or raise the urinary pH increase the risk of calcium phosphate stones.
Salty Foods
The main ingredient in salt is sodium chloride. Too much sodium consumption causes more calcium to be excreted into the urine, precipitating kidney stones made of calcium and phosphorus. Sodium also decreases urinary output by causing more water to be reabsorbed by the kidneys, further increasing the risk of stones. Processed foods, canned soups, hot dogs and cured meats are generally high in sodium and should be avoided by people with calcium phosphate stones.
Salt is not the only source of sodium. Monosodium glutamate (MSG), baking soda and baking powder, and the common preservative sodium nitrate all have sodium as the main ingredient. Avoid these ingredients or use them sparingly.
Citrus Fruits
Citrus fruits such as oranges and lemons have citrate, an alkaline substance that raises the pH of urine. As the urine pH rises, so does the risk of calcium phosphate stones. Avoid oranges, lemons, tangerines and the juices made from these fruits.
Some diet sodas contain higher amounts of citrate than homemade lemon juice. Consuming these beverages may increase the risk of kidney stones. People with calcium phosphate stones should not drink these beverages.
Non-Dairy Animal Proteins
Animal proteins increase urinary calcium excretion as more calcium is taken from the bones to neutralize the acidity of these proteins. People with calcium phosphate stones should avoid eating too much meat, fish and poultry. In general, limit the consumption of animal proteins to less than 6 oz. a day, which is roughly the size of two decks of cards. Proteins from dairy products are OK. Although dairy foods have more calcium, they do not increase the risk of calcium phosphate stones.
