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Kidney stones can form when substances in the urine such as calcium, oxalate, and phosphorus become highly concentrated. The body uses food for energy and tissue repair. After the body uses what it needs, waste products in the bloodstream are carried to the kidneys and excreted as urine. Diet is one of several factors that can promote or inhibit kidney stone formation. Other factors that affect kidney stone formation include genes, environment, body weight, and fluid intake. Few simple dietary modifications will help to reduce its recurrences.
Four major types of kidney stones :
• Calcium stones are the most common type of kidney stone and occur in two major forms: calcium oxalate and calcium phosphate. Calcium oxalate stones are more common. Calcium oxalate stone formation may be caused by high calcium and high oxalate excretion. Calcium phosphate stones are caused by the combination of high urine calcium and alkaline urine, meaning the urine has a high pH.
• Uric acid stones form when the urine is persistently acidic. A diet rich in purines substances found in animal protein such as meats, fish, and shellfish may increase uric acid in urine. If uric acid becomes concentrated in the urine, it can settle and form a stone by itself or along with calcium.
• Struvite stones result from kidney infections. Eliminating infected stones from the urinary tract and staying infection-free can prevent more struvite stones.
• Cystine stones result from a genetic disorder that causes cystine to leak through the kidneys and into the urine, forming crystals that tend to accumulate into stones.
How much fluid should a person drink to prevent kidney stone formation?
People who have had a kidney stone should drink enough water and other fluids to produce at least 2 liters of urine a day. The amount of fluid each person needs to drink depends on the weather and the person’s activity level people who work or exercise in hot weather need more fluid to replace the fluid they lose through sweat. A 24-hour urine collection may be used to determine the volume of urine produced during a day. If the volume of urine produced is too low, the person can be advised to increase fluid intake. Drinking enough fluid is the most important thing a person can do to prevent kidney stones. 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.
How does animal protein in the diet affect kidney stone formation?
Meats and other animal protein such as eggs and fish, contain purines, which break down into uric acid in the urine. Foods especially rich in purines include organ meats, such as liver. People who form uric acid stones should limit their meat consumption to 160 grams each day. Animal protein may also raise the risk of calcium stones by increasing the excretion of calcium and reducing the excretion of citrate into the urine. Citrate prevents kidney stones, but the acid in animal protein reduces the citrate in urine.
How does sodium in the diet affect kidney stone formation?
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 preferred to reducing calcium intake. Foods that contain high levels of sodium include canned soups and vegetables, processed frozen foods, fast food etc.
How does oxalate in the diet affect kidney stone formation?
Some of the oxalate in urine is made by the body. However, eating certain foods with high levels of oxalate can increase the amount of oxalate in the urine, where it combines with calcium to form calcium oxalate stones. Foods that have been shown to increase the amount of oxalate in urine include spinach, rhubarb, nuts, wheat bran and beer. Avoiding these foods may help reduce the amount of oxalate in the urine.
How does calcium in the diet affect kidney stone formation?
Calcium from food does not increase the risk of calcium oxalate stones. Calcium in the digestive tract binds to oxalate from food and keeps it from entering the blood, and then the urinary tract, where it can form stones. People who form calcium oxalate stones should include 800 mg of calcium in their diet every day, not only for kidney stone prevention but also to maintain bone density. A cup of low-fat milk contains 300 mg of calcium. Other dairy products such as yogurt are also high in calcium. Calcium supplements may increase the risk of calcium oxalate stones if they are not taken with food.
Points to Remember
• Kidney stones can form when substances in the urine such as calcium, oxalate, and phosphorus become highly concentrated. Diet is one of several factors that can promote or inhibit kidney stone formation.
• Four major types of kidney stones can form: calcium stones, uric acid stones, struvite stones, and cystine stones.
• Drinking enough fluid at regular interval is the most important thing a person can do to prevent kidney stones. People who have had a kidney stone should drink enough water and other fluids to make at least 2 liters of urine a day.
• 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 preferred to reducing calcium intake.
• Meats and other animal protein—such as eggs and fish—contain purines, which break down into uric acid in the urine.