One day when William Shatner was on the set of "Boston Legal," he was whisked off to the emergency room for acute lower back pain. It turned out he had a kidney stone.

When he passed it, he auctioned the stone off for $75,000, which he donated to a housing charity.

That’s great use of a wickedly painful kidney stone. But in general, it's better to take steps to avoid one from forming.

Kidney stones may indicate chronic kidney disease, osteoporosis, or cardiovascular disease. And once you develop a stone, there's a 30% chance you'll have another episode within five years. So researchers from the Mayo Clinic looked at how diet can help you dodge the problem.

Their study found that lower intakes of dietary calcium and potassium, as well as lower intake of fluids (less than 108 ounces of water from liquid and foods), caffeine, and phytate (a form of phosphorus in bran and seeds), are associated with higher odds of developing a symptomatic kidney stone for the first time.

But if your diet includes plenty of calcium- and potassium-rich foods, you may prevent a repeat attack.

A daily intake of 1,200 mg of calcium may help prevent first-time and recurrent kidney stones. Calcium is found in sardines, salmon, winter squash, edamame, almonds, and dairy.

Also aim for 3,400 mg (men) and 2,600 mg (women) of potassium daily. It's in dried apricots, prunes, raisins, orange juice, bananas, acorn squash, spinach, tomatoes, broccoli, legumes, nuts, and yogurt.