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DEAR MAYO CLINIC: Is diet always the cause of kidney stones, or are some people just more susceptible than others?
ANSWER: Diet can play a significant role in the formation of kidney stones, but it’s not the only reason a person may develop these stones. A family or personal history of kidney stones raises your risk, as do certain medical conditions. If you get a kidney stone, finding out what it’s made of will help determine steps that you can take to lower your risk, including ways to change your diet. By taking such steps, it’s less likely you’ll develop stones in the future.
Kidney stones are hard deposits of minerals and salts that form inside your kidneys. They develop when your urine contains more crystal-forming substances, such as calcium, oxalate and uric acid, than the fluid in your urine can dilute.
One of the most straightforward ways to lower your kidney stone risk is to drink plenty of fluids. Extra fluids dilute urine, making stones less likely. If you have a history of kidney stones, health care providers usually recommend passing about 2½ liters of urine per day. One way to gauge whether you have adequate fluid intake is to check the appearance of your urine. If it’s light or clear, you’re likely drinking enough fluids.
The amount of salt in your diet makes a difference, too. Taking in too much salt increases the amount of calcium your kidneys have to filter, and that raises your risk of kidney stones. Reducing the amount of salt in your diet may lower your risk of stones.
If you’ve already had kidney stones, knowing the type of stone you form will help with dietary choices to prevent future stones. For example, if your stones are calcium oxalate, you may need to limit foods rich in oxalates. They include certain fruits and vegetables, as well as nuts and chocolate. Uric acid kidney stones can form in people who don’t drink enough fluids, lose too much fluid or eat a high-protein diet. In that case, choosing a diet low in animal protein can help.
Crafting a diet to prevent kidney stones can be complicated, so if you’ve had stones, talk to a dietitian. He or she can review your situation and work with you to create an eating plan tailored to your needs.
Your health care provider also may recommend a test called a “metabolic urine profile.” This test involves analyzing your urine over a 24- to 48-hour period. It gives specific information about how your kidneys are working and helps identify modifiable risk factors for kidney stone development.
Heredity plays a role in kidney stones. People who have a family member with kidney stones are twice as likely to develop stones as those who don’t have that family history. And once you develop a kidney stone, your risk for future stones goes up. Most people get their first kidney stone between the ages of 40 and 60. After you have one stone, the chance of getting another within a year is about 15%. The likelihood of developing more stones in three to five years is 35% to 40%, and within 10 years, it’s 50%.
Finally, your medical history can contribute to the formation of kidney stones. Diseases and conditions that may increase the risk of kidney stones include inflammatory bowel disease, chronic diarrhea, renal tubular acidosis, cystinuria, hyperparathyroidism and urinary tract infections. High body mass index, large waist size and weight gain also are associated with kidney stones. Having gastric bypass surgery and taking certain medications can raise your risk, too.
If you’ve had kidney stones in the past, or if you’re concerned you may be at high risk for them, talk to your health care provider. He or she can review your risk factors with you and, if necessary, recommend steps you can take to help prevent kidney stones. — Dr. Mitchell Humphreys, Urology, Mayo Clinic, Phoenix