That kind of imagery sticks in your mind. I know it stuck in mine.

That was the description my colleague Pat used to convey the pain of a kidney stone, which I included in yesterday's e-alert when I told you how essential fatty acids can help prevent kidney stones.

Another new study reports that the kidney-stone-prevention diet that doctors have been recommending for years doesn't work. That's the bad news. But the good news is, the same study reveals what DOES work to reduce the urinary markers of kidney stones and reduce your risk of recurrence.

Does a low calcium diet REALLY help prevent kidney stones?

First, a bit of background: there are several different kinds of kidney stones, but 70 to 80 percent are composed of calcium and oxalate (also called oxalic acid). Oxalate is a type of salt found in certain foods, like walnuts, spinach, rhubarb, parsley, and chocolate.

Consequently, doctors have long advised kidney stone sufferers to lower their calcium intake to help prevent recurrences. But long-term research failed to show a benefit from this approach - and kidney stone recurrence rates remained right around 50 percent.

Some limited research had suggested that animal protein and salt intake might have more to do with kidney stones than calcium. So in this study, the researchers set out to compare the two dietary approaches.

They recruited a group of 120 men with a history of calcium oxalate kidney stones; the participants had to have urinary calcium excretion greater than 300 mg per day and at least two documented kidney stone events. Then they divided the men into two equal groups.

One group followed a traditional low-calcium diet, with only 400mg. of calcium intake each day.

The other group followed a low-protein, low-salt diet, with normal-to-high intake of calcium. Low protein was defined as 15 percent of total calories, or about 90 grams of protein for a 2,500 calorie diet. Sodium was restricted to about 2000 mg.

Both groups were told to avoid foods rich in oxalate, and to increase water intake to two liters a day in cold weather and three liters a day in warm weather. Each man's urine was evaluated at baseline, one week after randomization, and then once a year for five years (or until he had a recurrence.)

Dietary approach cut kidney stone recurrence rate in half. Over time, the low-protein, low-salt approach produced dramatic results. In the low-calcium diet group, 23 of the 60 participants had a recurrence. But in the low-protein group, only 12 of the 60 had another stone incident. That's HALF the recurrences, just from a dietary change.

Ironically, the low-protein group showed as much reduction in urinary calcium excretion as the low-calcium group - even though they consumed normal to high levels of calcium. But the low-protein group also decreased its excretion of oxalate, the other component of most kidney stones. In fact, in the low-calcium group, the oxalate excretion actually INCREASED.