Dietary prevention of kidney stones

Basic kidney stone diet:

Almost all kidney stone patients will benefit from simple dietary changes which include increasing their fluid intake and limiting certain types of food. Together, these simple steps have been shown to decrease the risk of forming another stone by 50% or more and will also improve overall health and well-being. A handout outlining these steps is available for download below. For more detailed information on dietary prevention read on further.

Specific dietary guidelines:

Fluid intake

Salt intake

Protein intake

Oxalate intake

Calcium intake

Fluid intake

A high fluid intake is one of the most important cornerstones of kidney stone dietary prevention. A sufficiently dilute urine will prevent the individual chemical components of stones from becoming concentrated enough to precipitate out of solution, keeping them instead in their dissolved state. A high urine output also may reduce stone from forming through “flushing” out of stone components and prevention of urine stagnation. In addition to stone benefits, increased water intake has been shown to have a multitude of other benefits, including improved alertness, better skin appearance, enhanced physical performance, reduced constipation, and enhanced weight loss.

The average daily urine output of normal healthy adults is 1.2 liters a day, ranging from 1 to 2 liters in most individuals and varying with body weight and gender. In stone formers, however, a higher daily urine output is required for stone prevention and achieving a daily volume of at least 2.0 to 2.5 liters a day can significantly reduce the recurrence of future stones. In a randomized study of stone formers who were given specific instructions to increase their fluid intake compared to stone formers told to not change their diet, those given specific fluid instructions achieved a high urine output of 2.6 liters a day versus 1.0 liters a day in those not given dietary instructions. Over a period of five years, the high fluid intake group was half as likely to form new stones as compared to the normal fluid intake group (Borghi et al, J Urol 1996).

We recommend that most stone formers increase their daily fluid intake by one liter (an additional two 16 oz water bottles or two tall glasses a day) in order to achieve a urine output of 2.5 liters a day. (One liter = 4.2 8-oz glasses or 34 oz).Alternatively, a 24 hour urine collection can be performed to guide fluid intake to achieve 2.5 liters of urine output in a specific patient.

Type of fluid intake

The type of fluid intake is generally less important that the total intake. While drinking water is our preferred recommendation because it is inexpensive and contains no calories, for stone patients who do not enjoy drinking water, any beverage will be beneficial in reducing stone risk.

Contrary to popular belief, studies have found that an increased intake of tea, coffee, and alcoholic beverage actually reduces the risk of stones, possibly because of an associated increase in urine output (Curhan et al, Am J of Epidemiology, 1996). While tea contains high levels of oxalate, this does not appear to result in increased stone formation for the reasons discussed below in our discussion on oxalate.

Soda intake (including colas) and milk intake also do not appear to increase the risk of stones.

Citrus fruit juices

Citrus juices, including lemon juice and orange juice, contain citrate, which acts as a stone inhibitor for calcium based stones. Citrate seems to do this by binding calcium, making it unavailable to combine with oxalate or phosphate: a necessary first step in the formation of stones. Citrate also seems to make it more difficult for stones to grow once they’ve formed.

Drinking citrus juice in the form of concentrated lemon juice mixed with water has been shown to effectively increase urinary citrate levels and reduce urinary calcium levels, both of which will reduce stone risk. Orange juice will similarly increase urinary citrate levels. However, orange juice appears to also increase urinary oxalate levels (a stone promoter). Other sources of citrate, including grapefruit juice, have had less research completed confirming their beneficial effects on urinary citrate levels. Therefore, lemon juice is typically favored over other citrus juices as a natural method to increase urinary citrate levels.  Many patients find drinking citrus juices to be an attractive alternative to pharmaceutical treatment with potassium citrate.

We recommend that stone formers consider supplementing their daily fluid intake with a mixture of 60 ml of concentrated lemon juice in one liter of water to increase their urinary citrate levels.

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Salt

A high sodium intake increases the risk of stone formation by increasing calcium levels and decreasing citrate (a stone inhibitor) levels in urine. Additionally, high sodium intake will impair the ability of medications such as hydrochlorothiazide to effectively reduce calcium levels in urine. A study of stone formers who were kept on a strict diet with a maximum daily sodium intake of 50 mmol (1200 mg) in addition to a reduced protein diet demonstrated that the low sodium diet was effective in reducing stone recurrence by 50% as compared to the low calcium diet.

We recommend that stone formers aim to follow the FDA’s guideline of limiting salt intake to 2300 mg of sodium a day in the general population and 1500 mg of sodium a day in those with hypertension, African Americans, or middle aged and older adults. 2300 mg is equivalent to about 1 teaspoon of table salt.

The best way to determine the salt content of your food is to read the nutrition label. Processed foods tend to contain higher amounts of salt. Choose low sodium options whenever possible.

• 1 cup of canned chicken noodle soup contains 870 mg of sodium
• A fried chicken drumstick contains 310 mg of sodium
• A serving of shrimp contains 240 mg of sodium
• 2 slices of white bread contains 200 mg of sodium
• 15 potato chips contain 180 mg of sodium
• 1 container of strawberry yogurt contains 85 mg of sodium
• 1 tomato contains 20 mg of sodium
• 1 apple contains 0 mg of sodium

In addition to lowering the risk of stones, a low sodium intake helps to control or prevent high blood pressure, which can lead to heart disease, stroke, heart failure, and kidney disease.

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Animal Protein

Animal protein in meat products increases the risk of stone by increasing calcium, oxalate, and uric acid levels in urine. All three of these changes increase the risk of stones. In studies comparing high meat eaters versus low meat eaters, high meat eaters were found to be at increased risk of forming stones.  A randomized study of stone formers restricted  to a low meat intake of 52 grams a day (equivalent to 8 0z of beef) in combination with sodium restriction found that the combination reduced stone recurrence by 50% compared to calcium restriction alone (Borghi et al, NEJM 2002).

We recommend that most stone formers try to reduce their meat intake to 6 oz a day. This includes all types of meat: beef, pork, poultry, and seafood.

The USDA recommends a daily allowance of 5-6 oz of protein intake among adults. They also recommend choosing non-meat protein foods such as nuts and beans instead of meat sources. Protein from non-meat sources does not appear to increase the risk of stones.

• A small steak contains about 3-4 oz of protein.
• A quarter pound hamburger with cheese contains 4 oz of protein.
• A chicken breast contains about 5 oz of protein, a chicken thigh about 2.5 oz, a chicken drumstick about 1.5 oz.
• One 5 oz can of tuna contains 5 oz of protein.
• 1 medium egg contains 1 oz of protein.

Lowering your animal protein intake and eating more fruits and vegetables also benefits your overall health by limiting the amount of saturated fats and cholesterol in your diet. This helps to reduce your risk of cardiovascular disease.

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Oxalate

While oxalate plays an important role in the development of calcium oxalate stones, dietary restriction does not appear to be effective in reducing the risk of stones in the majority of patients. About 40% of urinary oxalate comes from dietary sources while the remainder is naturally made within the liver. Therefore, reducing oxalate dietary intake does not always have a significant impact on total urinary oxalate levels.

Oxalate is found in many vegetable and fruits, including many healthy dietary choices often making it difficult to achieve a low oxalate diet. Because of these issues, oxalate avoidance is beneficial primarily in those individuals with specific abnormalities that lead to high oxalate urinary levels.

We recommend that most stone formers should maintain a normal oxalate intake without the need for oxalate restriction. High oxalate intake should be avoided in individuals found to have high urinary oxalate levels on metabolic evaluation. Oxalate restriction may be beneficial in certain individuals with high urinary oxalate levels.

Oxalate rich foods

• Tea (black)
• Spinach
• Mustard greens
• Chard
• Beets
• Rhubarb
• Okra
• Berries
• Chocolate
• Nuts
• Sweet potatoes

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Calcium

Kidney stone formers often question whether to stop or reduce their calcium intake. Despite the fact that calcium is a major component of 75% of stones, excessive calcium intake is very rarely the cause of stone formation. In fact, several studies have shown that restricting calcium intake in most stone formers actually increases the number of stones they develop. This appears to happen because when less calcium is ingested, it becomes easier for oxalate (which normally binds with calcium in the gut) to be absorbed. Higher levels of oxalate in the urine then lead to an increase in stone risk. Calcium obtained from dietary sources appears to be better than calcium from supplements in regards to lowering stone risk because supplements can actually increase your risk of stones slightly (by 17%) while dietary calcium intake is instead associated with lower stone risk. If you need to take supplements, taking them during meals appears to be better in terms of stone risk.

We recommend that stone formers maintain a normal calcium intake, preferably from dietary sources. Female stone formers taking calcium supplementation to prevent osteoporosis experience a slightly increased risk of stones (17%) which needs to be balanced against their risk of osteoporosis.

For more on calcium intake and stones, see: Should I stop my calcium?

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Editors note: Oxalate and calcium sections updated on 5/23/12 to reflect information presented at the 2012 American Urological Association Meeting.