A kidney stone is a hard mass that forms when some of the ingredients in urine crystallize, according to the National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC). Two of the four types of kidney stones are related to diet: calcium stones and uric acid stones. Different foods form different types of stones, so you should talk to your doctor to find out what kind of stone you have, so you'll know what foods to avoid.
Salt
Salt causes extra calcium to be excreted into the urine, where it can combine with oxalate or phosphorus to form calcium stones, according to the NKUDIC. If you are prone to calcium stones, it's a good idea to limit your salt intake to the U.S. Recommended Daily Allowance of 2400 mg a day. A good way to do that is to avoid processed foods because they tend to be high in salt. Cut back on hot dogs, canned food, frozen meals, tomato juice, deli meat and fast food.
Oxalate-Rich Foods
If you have calcium oxalate stones, you should reduce the amount of oxalate-rich foods you consume to prevent a recurrence, according to MedlinePlus. Oxalate is found in rhubarb, currants, canned fruit salad, strawberries, Concord grapes, spinach, beets, leeks, squash, wheat bran, sweet potatoes, tomato soup, tea, instant coffee, grits, tofu, nuts and chocolate.
Calcium Sources
It may seem logical to cut back on calcium-rich foods, like dairy products, to reduce the risk of calcium stones, but it's actually counter-productive, according to the NKUDIC. Calcium from food binds to oxalate in the digestive tract and keeps it from entering the urine where it can form stones. People at risk for calcium oxalate stones should try to get 800 mg a day of calcium from food by eating milk, cheese, yogurt, tofu, fortified orange juice or other sources of dairy. But don't take supplements without talking to your doctor first because some studies indicate they increase the risk of kidney stone formation, according to the NKUDIC. Taking supplements with meals, so they can bind with oxalate in your food, may reduce the risk.
Animal Protein
Animal protein from meat, fish and poultry may increase the risk of both calcium stones and uric acid stones, according to the NKUDIC. Meat and other animal proteins increase the level of calcium in the urine, which increases the risk of calcium stones and reduces the level of citrate that can protect against them. People who are prone to uric acid stones face a different risk from animal protein. Meat, poultry and fish are rich in purines, which form uric acid when they're digested, raising the risk of uric acid stones. Those who form uric acid stones should limit their meat consumption to 6 oz. a day, according to the NKUDIC.
High Purine Foods
People who are prone to uric acid stones can reduce their risks by avoiding high-purine foods, according to the NKUDIC. These include organ meats like liver or kidneys, alcohol, anchovies, sardines, herring, gravy and consommé. Some vegetables are also high in purines and should be avoided. These include legumes like beans and peas, mushrooms, spinach, asparagus, cauliflower and yeast. It's also a good idea to limit fatty foods like oil, fried foods and salad dressings, according to MedlinePlus.
