90% of the kidney-stones are calcium oxalate stones.

Although spinach is very healthy, it has lot of oxalic acid. If you have problem with kidney stones, you can eat it moderately and also drink at least 4 litres of water. There are several other vegetables having oxalates. Soya bean has the maximum amount of oxalates.

There is no oxalic acid present in tomato and you can use it wherever you like in your food.