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Prone to Kidney Stones? Watch What You Eat

July 20, 2001 -- Passing a kidney stone is said to be the only experience that approaches the painfulness of childbirth. One way the unlucky few who are susceptible to a certain type of kidney stone can prevent the grueling condition is to avoid certain foods. New research adds meat to that list.

Just like their name implies, kidney stones are small rocks that develop in the kidney. They are painful because they must be passed out of the body through the narrow canals, called the ureters and urethra, where urine flows first from the kidney to the bladder and then from the bladder out of the body. They occur when certain minerals in the urine come out of solution and form into a stone.

No one knows for sure why this happens, but people who have had kidney stones before or who have a family history of kidney stones are at high risk for developing them again.

The most common type of kidney stone is made up of calcium oxalate, thus preventing the buildup of oxalate in the urine could help prevent the development of stones.

About 10% of white men and nearly as many women will develop a kidney stone in their lives. People who are susceptible to oxalate stones can prevent the oxalate build up several ways:

• Drink plenty of fluids.
• Eat calcium-containing foods -- the calcium binds the oxalate in the gut preventing it from being absorbed.
• Avoid foods containing oxalates. Spinach seems to produce the most oxalate. Other oxalate-containing foods include beans, beets, berries, green peppers, chocolate, coffee, colas, peanuts, peanut butter, and wheat bran.

New research from Europe adds meat to the list of foods to avoid. A study in Kidney International has linked high amounts of oxalate in the urine to eating meat in people known to be at risk of developing oxalate kidney stones.

Senior author Philippe Jaeger, MD, says that, "The critical elements of nutrition that lead to [high oxalate in the urine] are excessive meat intake, ... [which includes] beef, poultry, and fish ... and excessive intake of sources of oxalate, ... which are peanuts and chocolate in particular," says study author Philippe Jaeger, MD. Not all people need to be cautious about these foods, however, just people who are susceptible to developing these kidney stones, adds Jaeger.

Jaeger soon will chair the department of nephrology at the University Hospital of the University of Nice Sophia-Antipolis in France.

Jaegar and his colleagues evaluated the urine of 33 men who ate a medium protein diet followed by a high protein diet. Of the participants, 20 had a history of kidney stones.

On average, the men with a history of kidney stones developed higher levels of oxalate in their urine while on the high protein diet compared with the medium protein diet. This pattern was not seen in the men with no history of kidney stones.

Donna Glad Blythe, MD, a board-certified kidney specialist practicing in Miami, agrees with the findings. "If you are a kidney stone former, you should not be on a high protein diet. ... Stone formers should decrease from a high protein diet to a medium protein diet."

That means restricting yourself to one 4 oz. serving of meat, poultry, or fish a day, which is an amount about the size of an average pack of cards. Blythe was not involved in the research.