Fizzy citrus diet drinks may help stop people developing painful kidney stones, research suggests.
An ingredient in some soft drinks could be a preventive measure for those at risk of the disorder, scientists say.
The drinks - 7Up, Sunkist, Sprite, Fresca and Canada Dry ginger ale - contain high amounts of a compound called citrate.
This is known to inhibit the formation of calcium oxalate stones, the most common form of kidney stone.
Researcher Dr Brian Eisner, of Massachusetts General Hospital in Boston, said that patients are advised to drink two to three litres of fluids a day to reduce the problem.
'If drinking these helps reach that goal, that may be a good thing,' he told the Journal of Urology, adding that he is not advocating that those prone to stones 'run out and get diet soda'.
Kidney stones develop when urine contains more crystal-forming substances - such as calcium, uric acid and oxalate - than can be diluted by the available fluid.
Potassium citrate supplements are 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.
In a study ten years ago, one of Dr 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, said Dr Eisner.
The current study investigated whether any commercially available drinks had a similar citrate content as the homemade lemonade.
Overall, the study found, citrus-based diet sodas - including 7Up, Sunkist Orange, Sprite, Fresca and Canada Dry ginger ale - had a higher citrate levels than the homemade lemonade. But dark colas had little or no citrate.
Dr Eisner is not advocating that those prone to stones 'run out and get diet soda'.
However, he pointed out that patients are routinely advised to drink two to three litres of water or other fluids each day in a bid to reduce the problem.
'If drinking these sodas helps people reach that goal, then that may be a good thing,' he said.
In a study ten years ago, one of Eisner's fellow researchers found that a homemade lemonade concoction was effective at raising the citrate level in the urine of those susceptible to forming stones.
Exactly how effective 'lemonade therapy' is at preventing stones remains unclear, but some doctors do recommend it to patients as a do-it-yourself treatment, said Dr Eisner.