How do you avoid kidney stone attacks?

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Q. I want to avoid another kidney stone attack. What's your advice about diet, coffee, tea, and alcohol?

A. The foods you eat and the amount of fluid you drink can contribute to some types of kidney stones. Certainly, you can help prevent recurrent kidney stones by paying attention to your fluid and food intake.

First and foremost, be sure you drink plenty of fluids every day and avoid dehydration. Kidney stones form when certain minerals concentrate in the urine and form hard crystals. By drinking plenty of fluid, you can decrease the concentration of these minerals. Aim to drink eight to 12 cups (64 to 96 ounces) a day.

The most common type of kidney stone is the calcium oxalate stone. In fact, about 80% of all kidney stones are made of calcium oxalate. The name might make you think you should eat a low-calcium diet to avoid getting them, but you should actually do the opposite.

Most people who develop calcium oxalate stones absorb too much oxalate. Oxalate is absorbed by the intestines and passes into the bloodstream. The body uses what it needs and sends the excess to the kidneys to excrete in the urine. In the urine, the higher concentration of oxalate can combine with calcium to cause kidney stones.

Many foods we eat, including some healthy ones, contain oxalate, so it is difficult to go on an oxalate-restricted diet. The best strategy is to make sure your diet is full of calcium-rich foods. Dietary calcium binds to oxalate inside your intestine, which means less oxalate is available to be absorbed into your bloodstream, and lower amounts passing through the kidneys.

Good dietary calcium sources include low-fat or fat-free dairy products, such as milk, yogurt, cottage cheese, and cheese. Other calcium choices include calcium-fortified orange juice, calcium-fortified soy milk, tofu, broccoli, sardines, collard greens, almonds, and black beans.

You also want to limit your protein, especially animal protein, as high amounts increase the likelihood of kidney stones. High-protein diets are acidic and reduce the number of natural stone inhibitors in the urine. Also, high-protein diets tend to contain more oxalate.

Tea and coffee in moderation are not a problem. While tea and coffee do contain some oxalate, the extra fluid outweighs any possible disadvantage. In fact, some studies suggest that drinking moderate amounts of tea and coffee can actually lower the risk of kidney stones. In general, if you do drink caffeinated beverages, keep your daily amount of caffeine to no more than 400 milligrams. That's equal to four or five cups of regular coffee.

It's a similar story for alcohol. Moderate alcohol use is associated with a reduced risk of kidney stones. But if you don't drink now, you don't need to begin to prevent kidney stones.

— Howard LeWine, M.D.
Editor in Chief, Harvard Men's Health Watch

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