Diet averts kidney stonesPublished 7:57pm Saturday, April 19, 2014
My recent experience with a kidney stone has sparked a personal interest in learning how to make sure that experience is my last. Often, we don’t sit up and take notice until necessity shakes us into new awareness.
You don’t want to be a ‘stoner’ but if you are, there are some things you can do to help prevent having the pain of passing a kidney stone. The kidney’s job is to filter waste products from the blood. Some molecules are returned to the blood and some are eliminated in urine. As the urine collects in the kidneys, stones can form by a complex process of super-saturation and crystal growth depending on circumstances such as urine volume, urine acidity and other products found in the urine. The risk is primarily affected by your family history, but is also increased in people with obesity, insulin resistance, diabetes, hypertension and inflammatory bowel disease. Aside from controlling your diseases, there are also food, nutrient and hydration choices that can decrease the risk of stone formations.
There are various types of stones (calcium oxalate, calcium phosphate, uric acid, struvite, and cystine) so getting one analyzed helps identify which dietary changes will be most helpful to prevent them from reforming. For the most part, though, the risk of stones increases in both men and women if urine has high amounts of substances such as calcium, oxalate or phosphorus. The risk is lower if there is more of a molecule called citrate and when urine volume is high. The chemistry is complex, but we will address some simple steps to reduce your risk. Mainly changes in the amount of sodium, animal protein, calcium, oxalate and fluids can make a difference.
Fluid and urine volume
Regardless of the type of stone, low urine volume is by far the most common problem leading to kidney stones. Keeping molecules diluted in the kidneys and a high flow of urine will help prevent or wash out any formed crystals. The goal should be to make 2 or more liters (approximately one half gallon) per day of urine. In the summer months or when you are sweating more from exercise, you may have to drink more fluids to continue produce this much urine. Drinking at night, during bathroom breaks, helps prevent urine from becoming too concentrated at night, which can lead to stone development with time. Soft drinks and colas that contain phosphoric acid should be avoided because they make urine more acidic. Some studies suggest citrus drinks, like lemonade and orange juice, protect against kidney stones because they contain citrate, which stops crystals from growing into stones.
Meats, fish, poultry, eggs, and cheese increase calcium excretion and decreases the protective citrate which can lead to calcium oxalate stones, which is the most common type. Proteins and grains are the main contributors of acidity in urine, which can lead to stone formation. The opposite of acid is alkaline (or basic). When acid-causing foods are not balanced with alkaline-causing foods, the result is chronic acidosis. It is important to include high-alkaline foods, which are fruits and vegetables. Examples of high alkaline foods are: all vegetables, but especially leafy greens; all fruits, but especially figs, apples, prunes, raisins, bananas; all herbs; molasses, brown sugar, cocoa and coffee. Some neutral foods are milk, white sugar, butter, oils and tea.
Animal protein also contains purines which break down into uric acid and can lead to uric acid stones. People with uric acid stones should limit meat to 6 ounces a day.
When the oxalate molecule makes its way to the kidneys it may bind with the calcium there to make crystals and eventually calcium oxalate stones. You can limit the foods that are high in oxalates if you form calcium oxalate stones. These foods are rhubarb, strawberries, spinach, whole-grain wheat/wheat bran, some nuts, beets and tea.
Fortunately, though, calcium eaten in the same meal binds with oxalate in the intestines so that the oxalate never makes it to the kidneys to cause trouble. Including 150 mg of calcium at each meal decreases the risk of calcium stones. You can get this amount by drinking a ½ cup of milk, or eating yogurt, ice cream, pudding or ¾ ounce of low fat cheese. Calcium supplements do not have the same protective effect as the calcium in foods and in some studies, they led to higher rates of stone formation in women. If you use calcium supplements, it is helpful to get what calcium you can from foods and make up the difference with pills that are taken with your meals only.
People who form kidney stones tend to have low to normal potassium intake and high sodium intake. Here’s another reason to eat more fruits and vegetables. Higher potassium foods include sweet potatoes, white potatoes, tomato paste, beans, yogurt, beet greens, bananas, peaches, melons and fish. Increasing potassium carries the bonus of a good effect on blood pressure.
Sodium, often from salt, causes the kidneys to excrete more calcium into the urine. High concentrations of calcium in the urine combine with oxalate and phosphorus to form stones. Reducing sodium intake is more effective and preferred to reducing calcium intake.
Limit processed meats, canned soups and processed frozen foods, and fast foods. Limit sodium to 2,300 mg daily.
In summary, the Dietary Approaches to Stopping Hypertension (DASH) diet formulated and studied by the National Heart, Lung and Blood institute at the National Institutes of Health has been found to reduce the risk of stone formation. It focuses on including ample fruits and vegetables, moderate dairy, low sodium and low animal protein. More can be found on this diet at www.nih.gov. Lastly, and most importantly, stay well hydrated by consuming enough fluids to keep the hinges busy on the bathroom door. I may just have to wear my shirttail untucked from now on.
Laurel MacKenzie, RD, LDN, CDE is a registered dietitian at Vidant Beaufort Hospital.