Diet soda for preventing kidney stones?

Certain diet sodas may have the potential to prevent the most common type of kidney stone, if new lab research is correct.

In the study, researchers found that the diet versions of several popular citrus-flavored sodas - like 7Up, Sunkist and Sprite - contained relatively high amounts of a compound called citrate. Citrate, in turn, is known to inhibit the formation of calcium oxalate stones, the most common form of kidney stone.

The findings, reported in the Journal of Urology, suggest that diet sodas could stand as an extra weapon for some people prone to forming kidney stones.

Kidney stones develop when the urine contains more crystal-forming substances - such as calcium, uric acid and a compound called oxalate - than can be diluted by the available fluid. Most kidney stones are calcium-based, usually in combination with oxalate.

One reason that certain people are prone to being "stone-formers" is that their urine contains relatively little citrate, explained Dr. Brian H. Eisner, a urologist at Massachusetts General Hospital in Boston and the lead researcher on the new study.

Potassium citrate supplements have long been a common treatment for preventing calcium oxalate stones, as well as another type of stone called uric acid stones, in people who are prone to them. And in a study 10 years ago, one of Eisner's fellow researchers found that a homemade lemonade concoction was effective at raising stone-formers'

urine citrate levels.

Exactly how effective "lemonade therapy" is at preventing stones remains unclear, but some doctors do recommend it to patients, according to Eisner.

The goal of the current study, he told Reuters Health, was to see whether any commercially available drinks had a similar citrate content as the homemade lemonade. The researchers chose diet soda, rather than regular, to avoid the high sugar and calorie content of the former.

Overall, the study found, citrus-based diet sodas - including 7Up, Sunkist Orange, Sprite, Fresca and Canada Dry ginger ale - had somewhat higher citrate levels than the homemade lemonade.

Dark colas, on the other hand, had little to no citrate.

Whether citrus-flavored diet sodas can actually help prevent kidney stones is still unknown. Eisner said he and his colleagues are currently conducting a study to try to answer that question.

For now, the researcher said he is not advocating that stone-formers "run out and get diet soda." However, he pointed out that patients are routinely advised to get 2 to 3 liters of water or other fluids each day.

"If drinking these sodas helps people reach that goal, then that may be a good thing," Eisner said.

He added that even in people who do not have naturally low urinary citrate levels, moderate amounts of the diet sodas are unlikely to do harm as far as stone formation goes. Many sodas do contain some sodium and/or caffeine; but again, Eisner and his colleagues say, when it comes to stone formation, there is no evidence that the sodium and caffeine levels in diet soda would present a risk.