Kidney Stone Prevention

The kidneys form the first part of the urinary system. They filter the blood to extract excess fluid and waste products. Urine, once made in the kidneys, travels through a tube on each side called a ureter to the bladder where it is stored until emptied to the outside.

Included within the materials filtered by the kidneys are minerals. Minerals are present in many of the foods that we eat. These minerals are absorbed during the process of digestion. The body uses the minerals that it needs, and the excess are excreted by the kidneys. Calcium, oxalate and uric acid are some of the minerals excreted by the kidneys.

Stones can form in the kidneys if an excess amount of calcium, oxalate or uric acid reaches the kidney at one time. If there is too much of one of these substances, it will not stay in solution in the urine. Rather, the minerals can join together and form crystals. Crystals can then join together to form a stone.

There are three core concepts to prevent stone formation: dietary awareness, adequate hydration and the use of inhibitors of stone formation. Dietary awareness can help reduce the risk for stones.

Adequate hydration means taking in plenty of water or other liquids so that there is enough fluid to reach the kidneys. The kidneys can then make a dilute urine (not a concentrated urine) and stone formation is less likely. One needs to make sure that there is adequate fluid reaching the kidney to keep the urine dilute. A good rule of thumb is to drink two large glasses of water with each meal. The majority of calcium, oxalate or uric acid reaches the kidney after eating a meal. Two glasses of water with each meal allows plenty of fluid to reach the kidney so that these materials do not become too concentrated and crystallization does not begin.

A third concept available for preventing stone formation is to increase the level of inhibitors of stone formation. There are some medications which can be used which will raise citrate (not citric acid) level in the urine. A high level of urinary citrate is a natural inhibitor to stone formation. Recent studies have suggested that lemonade made from real lemon juice raises urinary citrate levels and may lessen the risk for stone formation.

Finally, for patients with uric acid stones, treatment with Allopurinol may be recommended. Allopurinol reduces the level of uric acid formed by the body, which reduces the amount that the kidney has to filter. Allopurinol treatment is effective for lessening the potential for uric acid stone formation, but does not provide any benefit for patients who form calcium oxalate stones.

General Stone Prevention Diet

Hydration Recommendations

Drink a 12 ounce beverage with each meal (your choice).

Drink 20 ounces of water with 2 ounces of lemon juice (or Lemonade) three times per day between meal (low- calorie powered lemonade mix also OK).

Drink more in summer, when exercising, if flying frequently, or if you live in a hot/dry environment.

Rationale: Lemon juice contains citrate. Citrate acts as a shield against new stone formation.

A 4 ounce glass of orange juice or low sodium tomato juice can also be a good source of citrate. Avoid more than 4 ounces on a regular basis because these juices also contain oxalates.

Calcium Recommendations

Your daily diet should have 800 -1200 mg of calcium. A serving of liquid dairy (milk, ice cream, yogurt) would be 8-10 ounces. A serving of solid dairy like cheese is 1-2 ounces. Skim milk has as much calcium as whole milk and hard cheese has more calcium than soft. It is better to have dairy servings with meals. Avoid dairy after 8 pm. Dairy is the most common dietary source of calcium.

Rationale: Studies have shown that low- calcium diets will increase calcium oxalate stone risk. Oxalates and calcium bind together in your intestines and leave the body together thus reducing the amount of oxalate found in the urine.

Protein Recommendation

Decrease animal protein (beef, poultry, fish, eggs) to 8-10 ounces per day. A good example would be two decks of cards side by side = your daily animal protein. Have one animal-protein-free day each week.

Rationale: A diet high in protein increases your body’s acidity. To combat this, your body releases calcium from your bones into your bloodstream that is eventually expressed into your urine.

Salt / Sodium Recommendations

Limit daily consumption of sodium to 2,500 mg per day.

Keep the salt shaker off the table. Read food labels.

Replace sodium- rich foods with potassium-rich vegetables such as avocado broccoli, romaine lettuce, and bell peppers.

Rationale: Sodium and calcium leave the kidneys together. Diets high in sodium lead to more calcium ending up in your kidneys and in your urine. The higher calcium level may increase your risk of forming new stones.

Oxalate Recommendations

Six (6) servings of oxalate-containing foods is OK daily. Limit your fat intake to decrease your oxalate levels. Careful consumption of foods with higher oxalate is required. Oxalate levels in foods are affected by time of year and growing conditions.

Rationale: Excess fat binds with calcium in food leaving oxalate by itself to be reabsorbed by the colon and back into the bloodstream. If too much oxalate is absorbed, it will combine with calcium in the kidney and can lead to calcium oxalate stones.

Frequently Asked Questions: (FAQs)