People with epilepsy are sometimes put on a high-fat, low-carbohydrate diet to reduce the likelihood of seizures, but one of the side effects is developing kidney stones.

Using a food additive, occasionally added to soft drinks as a buffer, could be the solution to reducing the calcium levels that promote development of kidney stones, say researchers from Johns Hopkins University.

In a study of 301 patients, they found that adding potassium citrate to the special diet as soon as it was begun limited the risk of developing kidney stones by a significant margin.

For those who took 1,170 milligrams of the supplement a day as soon as they began the diet, the risk was seven times lower than for those who only received the powdered additive once they started showing signs of stone development.

"We can confidently say this is a safe and powerful way to prevent kidney stones, and it should become part of standard therapy in all ketogenic dieters, not just those who already show elevated urine calcium levels," says senior investigator Dr Eric Kossoff.

More than 2 million Americans are diagnosed with epilepsy, according the the Centers for Disease Control.