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.