The longstanding advice to cut calcium from your diet to prevent kidney stones from recurring is based on rocky scientific evidence, a new study says.

A diet with normal amounts of calcium, but that’s modest in meat and salt, is nearly twice as effective as a low-calcium diet at preventing kidney stones from recurring in men. Research conducted at the University of Parma in Italy and reported in this month’s New England Journal of Medicine, is an about-face from earlier thinking. Although kidney stones are largely composed of calcium, denying the body of that mineral appears in fact to promote stones and deprives the skeleton of a critical building block.

“I think by putting someone with kidney stones on a low-calcium diet you’re taking a great risk that this will lead to a depletion of their bone mineral,” says David Bushinsky, a kidney expert at the University of Rochester in New York. “It’s a sure way to promote osteoporosis,” especially in older women, he says.

In the Italian study, researchers randomly assigned 120 men with a history of kidney stones to either a low-calcium diet (400 milligrams per day) or a diet low in salt and protein with normal calcium intake (1,200 milligrams per day). After five years of follow-up, 23 of the 60 men on the low-calcium diet had developed new kidney stones. But just 12 of the 60 men in the low-salt, low-protein, normal-calcium diet had recurring stones.

“Our study suggests that a diet characterized by normal calcium, low animal protein, and low salt levels is more effective than the traditional low-calcium diet for the prevention of recurrent stones,” the researchers say. “We speculate that this type of diet will be of greatest value when it is started early in the course of the disease.”

This study was the first direct comparison of the two diets. Women were not included in the study due to the risk of osteoporosis.

Health Scout News, Associated Press