'DASH' diet may prevent kidney stones

By Amy Norton

NEW YORK (Reuters Health) - A diet widely recommended for lowering blood pressure may also curb people's risk of developing kidney stones, a new study suggests.

The diet, known as Dietary Approaches to Stop Hypertension (DASH), advocates eating plenty of fruits, vegetables and whole grains, and moderate amounts of low-fat dairy and lean meat and fish.

In the new study, adults with the most DASH-like diets had a 40 percent to 45 percent lower risk of developing kidney stones compared with those whose eating habits least emulated the DASH diet.

The study, published in the Journal of the American Society of Nephrology, was not a clinical trial that directly tested the effects of DASH on kidney stone risk.

Still, the findings argue against one common dietary tactic taken by people susceptible to kidney stones, according to Dr. Eric Taylor and his colleagues at Harvard Medical School in Boston.

Most kidney stones are made up of calcium in combination with a compound called oxalate, the food sources of which include certain fruits, vegetables, grains, nuts and legumes. So some people with a history of kidney stones avoid oxalate-containing foods.

However, Taylor told Reuters Health, study participants with the most DASH-like diets had a lower kidney stone risk despite consuming more oxalates on average.

He and his colleagues say that it might make sense for people with a history of kidney stones and very high oxalate levels in their urine to avoid certain foods particularly high in oxalates -- like spinach and almonds.

But the current findings suggest that "stone formers" should not strictly limit fruits, vegetables and other generally healthy fare in their diets, according to Taylor's team.

The researchers based their findings on data from three large studies of U.S. health professionals.

The studies included a total of nearly 242,000 men and women who were followed for an average of 14 to 18 years. During that time, participants periodically completed detailed questionnaires on their diets and other lifestyle habits.

Overall, those whose diets most closely adhered to DASH advice had a lower risk of developing kidney stones over the study period. The link held when the researchers weighed other factors that affect kidney stone risk, such as body weight, high blood pressure and fluid intake.

Since many people with kidney stones also have high blood pressure, DASH may be an especially valuable diet for them, Taylor said.

He stressed that it is important for patients to work with their doctors to individualize their diets -- based, for example, on the type of kidney stones they have. (A minority are composed mainly of compounds other than calcium and oxalate.)

"However," Taylor added, "we think a DASH-style diet holds great promise as a way to reduce the risk of recurrence in individuals with a history of kidney stones."

SOURCE: Journal of the American Society of Nephrology, online August 13, 2009.