Dear Doctors: I recently passed a kidney stone. How likely am I to have a recurrence? I have been drinking more water as recommended, sometimes I eat fish but never red meat or poultry, and I get plenty of fruit and vegetables. Also, do I really have to avoid nuts and peanut butter?
Dear Reader: Kidney stones are bits of hard, pebblelike debris formed from the salts and minerals contained in the kidney. They range in size from smaller than a grain of sand to (yes, this is a Guinness World Records rarity) as large as a golf ball. Kidney stones are notorious for the pain they cause as they leave the kidney. This is because the tube that carries urine to the bladder has a limited ability to stretch. Known as the ureter, it spasms to force the stone out. Depending on the size of the stone, the exit can take a few days to weeks. Very large stones can become stuck and require medical intervention.
Kidney stones are categorized by the crystals from which they are composed. Uric acid stones are linked to eating large amounts of animal proteins, and struvite stones form in response to chronic urinary tract infections. The most common are calcium-oxalate stones, which are tied to urinary chemistry. This includes levels of calcium, sodium, citrate and oxalate in the urine. Also important is the amount of water in the urine. When you drink too little, urine becomes concentrated. This creates an optimal environment for dissolved minerals and salts to form crystals. Drinking plenty of water keeps urine diluted, which helps prevent kidney stones from forming.
Managing your diet can also be helpful. Certain foods, such as spinach, Swiss chard, beets and rhubarb, are high in oxalate. These can add to the body's oxalate load and may have an adverse effect on urinary chemistry. Our bodies also produce a significant amount of oxalate. That means factors beyond diet, including genetics, also play a role in kidney stones forming.
As for your regret about giving up nuts and peanut butter, which are often included in lists of high-oxalate foods, there is encouraging news. For many people, these foods do not need to be eliminated but can be enjoyed in moderation. Pairing higher-oxalate foods with foods that contain calcium can reduce how much oxalate gets absorbed in the gut. This means less oxalate reaches the urine where stones form. Getting enough calcium in your diet can be protective. At the same time, it is important to limit excess sodium, which can increase the amount of calcium excreted in the urine.
It is estimated that 10% of people will experience a kidney stone during their life. Unfortunately, having had one puts them at higher risk of another. You are making a wise choice by focusing on both diet and hydration in your effort to lower your risk. If, despite your best efforts, kidney stones recur, your doctor may suggest you do a metabolic evaluation. This can help pinpoint the most effective prevention strategies.
(Send your questions to [email protected], or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
