The kidneys play a crucial role in removing waste products and excess fluid from the body. Urine is the end- product of this filtering activity of the kidneys. Substances such as calcium, oxalate and phosphate are normally dissolved in the urine. Sometimes these substances separate out as crystals in the urinary tract and accumulate there over a period of time forming kidney stones. Heredity, environment, weight, fluid intake and diet all play an important role in determining the risk of developing kidney stones. A stone may stay in the kidney or break loose and travel down the urinary tract. A small stone may pass all the way out of the body without causing too much pain. A larger stone may get stuck in a ureter, the bladder, or the urethra. A problem stone can block the flow of urine and cause great pain.
People who have had a kidney stone before are more likely to have a new kidney stone. Thus it is very important for these people to determine the cause of their stone and plan their diet and do some lifestyle changes that reduce the risk of forming stones. Medications may also be prescribed depending on the type of stone a person had to reduce the risk of developing a new stone.
Simple dietary changes that may reduce a person’s risk of kidney stones include:
- Drinking water and other fluids: Drinking enough water dilutes the urine and flushes away the substances that form stones in the kidneys.
- Reducing salt intake: The more sodium you consume, the more calcium is excreted in the urine, thus increasing the risk for kidney stones. Foods rich in sodium should be avoided including fast foods, packaged or canned foods, salty snacks, softened water and sports drinks. Some food ingredients have hidden salt content. These include monosodium glutamate (MSG), baking soda, baking powder, disodium phosphate, sodium alginate and sodium nitrate or nitrite. Use of such food ingredients should also be avoided. Sodium intake should be less than 2 g per day.
- Decrease animal protein intake: Excess consumption of foods rich in animal proteins such as meats, eggs and fish increases the risk of uric acid stone formation. Daily meat consumption should be less than 170g per day.
- Consuming adequate calcium through foods: Calcium supplements in the form of tablets and capsules should be avoided. However, the calcium from food binds the oxalate from food in the digestive tract and prevents it from entering the blood and the urinary system, thus preventing kidney stone formation. Two servings of dairy or other calcium rich foods per day are generally recommended. This also helps to maintain bone density. People who had calcium oxalate stones in the past should have 800mg of calcium per day in their diet to reduce the risk of new kidney stone formation.
- Avoid certain foods: Avoid eating foods containing high amounts of oxalate such as spinach, rhubarb, nuts and wheat bran.
- Avoiding intake of nutritional supplements containing Vitamin C or Vitamin D: A person with a tendency to form kidney stones should consult a doctor before taking any nutritional supplements.
Being overweight may also increase the risk of developing kidney stones. Thus maintaining a healthy weight through healthy food choices and exercise may help reduce the risk of stone formation.