One of the treatments for certain types of calcium kidney stones is to reduce the amount of protein in the diet. Physicians will refer the patient to a registered dietitian for modification of the diet.http://gicare.com/Diets/Kidney-Stone.aspx
With high protein diets, It was originally thought that the excess calcium being excreted in the urine was coming from the bones. This would result in in osteoporosis and fragile bones. This was one of the criticisms of the Adkins diet (lo carb, high protein). There are a few new studies which claim that the calcium is not coming from the bones but rather from increased absorption from the GI tract. There are also a few recent studies that have found that people who consume more than the recommended dose of protein (.8 grams of protein per kg of body weight) have stronger bones.
This finding has some experts calling for a higher amount of protein in the diets of populations predisposed to osteoporosis.http://lowcarbdiets.about.com/od/faq/f/lowcarbboneloss.htm
Thiazide diuretics (a commonly prescribed blood pressure medication) can reduce the amount of calcium secreted in the urine by the kidneys. Because of this calcium sparing effect, thiazide diuretics are used to prevent calcium stones.