Kidney stones are formed when substances present in the urine such as calcium, oxalate, and phosphorus become highly concentrated. In the human body, food is used for energy and tissue repair. After the body has used what it requires, the waste products are carried to the kidneys and excreted as urine. Our diet plays an important role in the promotion and inhibition of kidney stones because the waste products excreted originate in our diet.
Types of Kidney Stones
The four major types of kidney stones are:
- Calcium stones – most common type of kidney stone and occurs as calcium oxalate and calcium phosphate.
- Uric acid stones – formed due to persistently acidic urine. Protein-rich diet contains purine, which can increase uric acid content in urine.
- Struvite stones – kidney infections cause this type of stone.
- Cystine stones – arise due to genetic disorder causing leakage of cystine through the kidneys into the urine.
Another important factor in kidney formation is urine volume. Very low volume of urine or highly concentrated urine contributes to the supersaturation of elements such as calcium oxalate.
Dietary Changes to Prevent and Reduce Kidney Stone Formation
Kidney stone formation can be reduced to some extent by increased urine volume that in turn reduces supersaturation of urine. The best fluid to increase urine volume is water. Water is non-caloric, non-caffeinated, and contains minute quantities of solutes. It is advisable to avoid high sugary beverages in large quantities. Black tea contains high amounts of oxalates and is not recommended for people with kidney stone problems. People with kidney stones must drink approximately two liters of fluid per day.
Limit dietary oxalates: Although only about 20 percent of urinary oxalates are derived from dietary sources, it is always recommended for people who tend to get oxalate kidney stones. Some common foods that contain high levels of oxalate include nuts, beans, rhubarb, spinach, beets, black tea, and chocolate.
Limit sodium intake: High-sodium diets are linked to greater calcium excretion because sodium and calcium compete for reabsorption in the renal vessels. This results in high calcium concentration in urine, which combines with oxalate and phosphorus to form kidney stones. Since processed and canned foods contain high amounts of sodium, it is better to avoid these foods.
Limit animal protein: Purines in animal protein are a major contributing factor for kidney stone formation. Excess protein creates concentrated urine and there is no inhibitor of uric acid crystallization. Dietary intake of 12 ounces of animal protein per day is recommended, which is sufficient to meet the dietary needs of adults. Plant proteins from beans and legumes can be included in the diet with no negative consequences.
A dietician can educate a person about dietary modifications that help reduce the occurrence of kidney stones. The Dietary Approach to Stop Hypertension (DASH) diet can reduce the occurrence of kidney stones. The DASH diet incorporates generous amounts of fruits and vegetables and moderate amounts of low-fat dairy products and animal protein.
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