Diet cola ----> Kidney stones?

[Koxinga]

A guy recently told me that he had had frequent problems with kidney stones, and that his doctor had warned him that drinking diet colas were a big risk factor for developing them. I knew about milk, but diet cola? He said that he once had a diet-cola induced kidney stone, and when it came out, the stone had the same caramel color as the stuff that had caused it.

If this weren’t a firsthand account, I might dismiss it as an urban legend. I still wonder if the guy might have been pulling my leg. What’s the straight dope?

[choosybeggar]

From an NIH site on kidney stones:

People prone to forming calcium oxalate stones may be asked by their doctor to cut back on certain foods on this list:
Beets
Chocolate
Coffee
Cola
Nuts
Rhubarb
Spinach
Strawberries
Tea
Wheat bran
People should not give up or avoid eating these foods without talking to their doctor first. In most cases, these foods can be eaten in limited amounts.

Calcium oxalate stones are one of the most common but not the only type of kidney stone. I couldn’t find any specific mention of diet cola.

Also, I found a reference to dairy products on the same site:

People who form calcium stones used to be told to avoid dairy products and other foods with high calcium content. But recent studies have shown that foods high in calcium, including dairy foods, help prevent calcium stones. Taking calcium in pill form, however, may increase the risk of developing stones.

So your dairy data are dated (try saying that 10 times fast :)).