Being obese or gaining weight more than normal increases the risk of kidney stones, especially in women who ordinarily run half the chance that men do of developing the painful deposits, researchers stated.

"Fat tissue may decrease the body's ability to respond to insulin, which could cause changes to the urine that favor the growth of kidney stones," said Eric Taylor, a physician at Boston's Brigham and Women's Hospital.

He said more research needs to be done to confirm that hypothesis but the study he led "found such a dramatic link between weight gain and kidney stones" that the next step is to find out if losing weight will lower the risk of having the condition repeat itself.

His report found that men who had gained 35 pounds (16 kg) since early adulthood were about 40 percent more likely to suffer kidney stones while women who gained the same over a similar period were about 70 percent more likely to have them, compared to people with normal weights.

Women with the largest waist circumferences studied had a 71 percent greater risk of kidney stones compared to those with the smallest waists. Men with the biggest waist sizes had a 48 percent greater risk.

The study, published in this week's Journal of the American Medical Association, offered no explanation for the differences between men and women. Ordinarily, it said, about 10 percent of U.S. men and 5 percent of women develop kidney stones over their lifetimes -- and U.S. treatment costs run about $2 billion annually.