Kidney stones are formed in the urinary tract when crystals come together, aggregating to form a mass large enough to be called a “stone”. They can be very painful and cause large numbers of emergency room and hospital admissions each year. The big question for chocolate lovers is whether chocolate must be avoided in those known to be at risk for nephrolithiasis (kidney stones). When it comes to gout and kidney stones, doctors usually advise their patients to avoid foods rich in substances that are implicated in the development of the disease. Is there a proven link between a food containing a risk substance and the actual end problem (in this case urinary stone formation)?
Oxalate, a substance found in many natural foods, is known to be implicated in the formation of certain types of kidney stones. Scientific studies have shown that dark chocolate is a rich source of oxalate, and that consumption of dark chocolate increases oxalate levels in the urine. Does this mean that dark chocolate must be avoided by those at risk for kidney stone formation?
Because of the complex nature of kidney stone formation, the best answer for each individual is to be obtained by them from their own doctor. The reason for this are multiple. First, the other, non-chocolate components of diet also dramatically affect the chance that oxalate kidney stones will form in a person eating foods rich in oxalates (some of the other oxalate rich foods are spinach, rhubarb, beets, nuts, tea, wheat bran, and strawberries). Even though calcium stones or calcium-oxalate stones are very common, less oxalate is excreted into the urine if adequate calcium is consumed in the diet. So a person eating substantial amounts of dark chocolate may not excrete risky levels of urinary oxalate if their diet also contains plenty of calcium. Rich common sources of dietary calcium are dairy products, certain antacids and supplements To further prove this point, researchers found that consumption of milk chocolate does not raise the urinary level of oxalate. It seems that a proper balance of dietary calcium and oxalate can minimize or eliminate the risks of dietary oxalate in those at risk of forming nephroliths.
Second, the most fundamental first level of treatment to prevent kidney stones is to increase hydration. It is known that drinking water allows the urine to be more dilute, thus lessening the chances that kidney stones will form. So your doctor may advise you that you must increase your fluid intake rather than worry about the otherwise healthful foods such as dark chocolate that are rich in oxalate.
Finally, even more complex factors such as the acid-base balance of the urine and the use of medications will influence the advice your physician gives you regarding the dietary intake of chocolate.