Kidney stones form when minerals and other substances in urine crystallize and clump into hard masses or stones. A number of factors may cause this to happen, including urinary tract infections, kidney disease and various inherited disorders or conditions that favor the formation of stones. Foods aren't likely to cause stones to form, though, unless you are already susceptible to them.

Kidney stones travel through narrow tubes that deliver urine from the kidneys to the bladder. Tiny stones may pass through these tubes, or ureters, without symptoms, but larger stones can cause excruciating pain in the back, side or abdomen. Symptoms may also include nausea, vomiting, blood in the urine, and fever and chills if an infection has developed.

Who's most likely to develop kidney stones? Middle-age men, but they can occur in adults of all ages. When they do, the treatment varies. Most small stones don't require medical intervention, but larger stones that cause persistent pain or other complications may be treated with a variety of techniques, none of which typically involve surgery. (For more detail about kidney stones, go to the National Kidney and Urologic Diseases Information Clearinghouse at http://kidney.niddk.nih.gov.)

Drinking plenty of water -- up to 2 or 3 quarts per day -- can help flush a kidney stone out of the ureter and into your bladder. Other than drinking plenty of fluids, though, your diet is likely to be more helpful in preventing future stones than in treating the ones that already exist.

Specific recommendations depend on the type of stones you form. Medications may be necessary in some cases, too. Blood and urine tests -- or analysis of a stone that's been passed and saved -- can help determine dietary changes that may help. The vast majority of kidney stones, though, are composed of calcium and oxalate -- a component of some fruits, vegetables, grains and legumes.

And contrary to what you might guess, you don't have to restrict your intake of calcium-rich foods to prevent calcium oxalate stones (although calcium supplements taken between meals may increase the risk of stones).

It's more important to reduce the amount of salt and sodium-rich foods you eat, including salty soups, condiments, fast foods and processed foods, and cut back on animal proteins, especially meat, cheese, eggs and poultry. Sodium and animal proteins cause you to lose calcium in your urine and may contribute to the formation of kidney stones.

People prone to forming calcium oxalate stones also need to limit foods high in oxalates. Those include chocolate, nuts, rhubarb, spinach, peanut butter, dark leafy greens, strawberries, wheat germ, soy foods and sesame seeds. Unfortunately, most of these high-oxalate foods are also super-nutritious, the kinds of foods most of us need to eat in greater amounts. Your health care provider will give you individualized advice, and it's likely you'll be able to eat some -- but not a lot -- of these otherwise-good-for-you foods.

More water, less sodium, less animal protein. Perhaps you recall hearing that advice from me before. That's because the same recommendations that help prevent kidney stones generally reduce the risk of other chronic diseases and conditions, too.

Eat a diet rich in whole, unprocessed foods, reduce your reliance on protein-heavy and fatty animal products, watch the sodium and added sugar and get regular exercise. It's a prescription for overall good health.