Ask Well: What Foods Should I Avoid to Prevent Kidney Stones?

Q. What foods should I avoid if I’m prone to kidney stones?

A. Drink more fluids, consume less sodium and eat a diet that includes calcium-rich foods. The rest depends on the chemical composition of your stones.

More than 90 percent of stones contain calcium, usually in the form of calcium oxalate, calcium phosphate or hydroxyapatite. Less often, stones are formed of uric acid or other chemicals. Different types of stones can also occur in the same person.

Since most stones contain calcium, doctors historically advised patients to limit the amount of calcium in their diets. It was a logical recommendation, but it was wrong.

In the early 1990s, a group of Harvard doctors followed for four years more than 45,000 men who had never had a kidney stone and came to a surprising conclusion: Diets that are high in calcium actually decrease the risk of kidney stones.

The group continued to follow these patients for 14 years and again found that dietary calcium protected against stones, though the protective effect was evident only in men younger than 60.3 Diets high in magnesium, potassium and fluids also appeared to be protective.

In 2005, the group expanded their analysis to more than 240,000 patients. They found that obesity and weight gain, particularly in women, increased the risk of stone formation.

This led them to study the DASH diet — a diet high in fruits, vegetables, nuts and legumes, low-fat dairy products, and whole grains; and low in sodium, sweetened beverages, and red and processed meats. The DASH diet is endorsed by the American Heart Association and the National Institutes of Health. The Harvard group found that DASH decreased the risk of kidney stones.

Such dietary recommendations can easily become overwhelming. Fortunately, the American Urological Association makes it simple:

• Drink at least 2.5 liters — about two-thirds of a gallon — of fluids per day.

• Limit sodium intake to 2,300 milligrams a day.

• Consume 1,000 to 1,200 milligrams of dietary calcium a day.

A common misconception about fluids deserves special mention. Water is not the only fluid that protects against kidney stones. Water, coffee, tea, wine, alcoholic beverages and orange juice all seem to be protective. Soda and other sugary beverages, on the other hand, increase the risk of stone formation.

Finally, check with your doctor, who can offer specific recommendations depending on the chemical composition of your stones.