• Kidney stones, hard chemical clumps of crystals in the urinary tract, are a common disorder. The most common type of stone contains calcium and either oxalate or phosphate, which are found in food and form human bone and muscle, but there are several other types as well. Avoiding some types of foods can help prevent stone formation in people who are likely to develop them.
  
  

Who is Most at Risk

• The number of Americans who have kidney stones has been increasing over the past 30 years, although why is unclear, the National Kidney and Urological Diseases Information Clearinghouse (NKUDIC) reports. They now affect more than 5 percent of the population. Incidence is higher in Caucasians than African-Americans, and men between the ages of 40 and 80 are most at risk. People with a family history of kidney stones or disorders and hyperparathyroidism, a metabolic disorder, are also more likely to develop stones than others. Those who have already formed stones are more likely than others to do so again.
  
  

Foods to Avoid

• People who eat high amounts of protein are more likely to develop uric acid stones, which represent up to 15 percent of those reported, according to an article in the April 2003 issue of the European Journal of Nutrition. People at risk should avoid eating meat, fish, seafood, legumes and chocolate, advises Naturopath Darin Ingels, ND, MT (ASCP) of the Bastyr University. Meat, poultry and fish can also contribute to calcium oxalate stone formation.
  
  Although a vegetarian diet may reduce stone formation, some vegetables should be avoided to prevent the formation of calcium oxalate stones. According to the Oxalosis and Hyperoxaluria Foundation, people with high amounts of oxalate in their urine may be advised by their doctors to avoid eating certain greens, such as spinach, rhubarb and swiss chard, okra, beets, wheat germ, soybean crackers, peanuts, chocolate, black Indian tea and sweet potatoes.
  
  Foods with somewhat less oxalate that can be eaten in limited amounts include grits, grapes, celery, red raspberries, fruit cake, strawberries, marmalade and liver.
  
  High salt intake also increases the risk of developing kidney stones, James Kenney, Ph.D, RD, FACN, reports on the Food and Health Communications website.
  
  

Foods to Eat

• Foods high in calcium, including dairy products, can help prevent the formation of calcium stones, according to NKUDIC and James Kenney. He also noted that the urine in many patients who have calcium oxalate stones is low in citric acid, magnesium and potassium. Foods that are rich in these nutrients--which includes many fruits and vegetables--help prevent stone formation. Examples include broccoli, blueberries, apples, lemons, tomatoes and carrots.
  
  

Other Precautions

• Although eating food that contains calcium can be preventative, calcium supplements may trigger the formation of stones, NKUDIC warns. Food supplemented with vitamin D, and some antacids that have a calcium base, should also be avoided.
  
  People who are at risk of developing kidney stones should stay hydrated, preferably by drinking enough water to produce at least 2 quarts of urine every 24 hours to help flush crystals from the urinary tract.