Chemicals in most people's urine effectively keep crystals from forming. When this process is inefficient, crystals composed of calcium plus oxalate or phosphate, or from uric acid, form. Some crystals pass through the urinary tract with ease; others cause tremendous pain. According to the National Digestive Diseases Information Clearinghouse, NDDIC, these stones, known as kidney stones, are one of the most painful urological conditions in existence. Avoiding certain foods may help to prevent stones from developing.
Oxalate is produced by the body and is present in a variety of foods. When oxalate builds up in the body, it can cause high levels of acid in the urine and trigger the development of calcium oxalate stones. According to the NDDIC, calcium oxalate stones are the most commonly diagnosed form of kidney stones. Foods high in oxalate include beets, chocolate, instant coffee, berries, concord grapes, okra, rhubarb, peanuts, spinach, Swiss chard, soybean crackers, wheat germ, spiced Indian tea, beer, and sweet potatoes.
Purines are substances that occur naturally in foods. Foods rich in purine-content may promote crystals in the urine that lead to uric acid stones, according to the NDDIC. For this reason, people prone to uric acid stones prevent or reduce stone development by avoiding organ meat, anchovies, gravy, sardines, and sweetbreads, which are rich in purine content. Foods moderate in purines include asparagus, bacon, beef, carp, cauliflower, chicken, cod, crab, halibut, ham, kidney beans, lamb, lentils, Lima beans, lobster, mushrooms, salmon, shellfish, snapper, spinach, trout, tuna, turkey, veal, and venison. According to the National Kidney Foundation, people who are prone to kidney stones may benefit from reduced animal-based protein intake, or consuming no more than four to six ounces of meat, poultry or fish per day.
Sodium found in salt and salty foods can cause the body to expel excessive amounts of calcium into the urine, which increases the risk of crystals in the urine. According to the NDDIC, limiting sodium intake is more valuable than limiting calcium intake in preventing calcium oxalate kidney stones. Foods particularly high in sodium include fast food, French fries, canned soup, frozen entrees, bullion, gravy, potato chips, tortilla chips, pretzels, beef jerky, seasoned bread crumbs, processed deli meats, cheese-topped pizza, ready-to-serve tomato sauce, and pickles. Replacing table salt with natural herbs and low-sodium seasoning blends can also help to reduce sodium intake and prevent crystal formation.