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Parklands Kidney Centre > Kidney Education > Diet and Kidney Stones

If you have kidney stones, you may need to follow a special diet. First, your doctor will run tests to find out what type of stones you form. From these, the doctor can determine which diet changes may be right for you. A registered dietitian can help you make the necessary changes in your diet.

What is a kidney stone?

A kidney stone is a hard mass that forms from crystals in the urine. In most people, natural chemicals in the urine stop stones from forming.

Are all kidney stones the same?

No. The most common types of kidney stones are made from calcium and oxalate. Individual treatment for kidney stones depends on the type of kidney stones that are formed.

Is there a diet I can follow to prevent me from having more kidney stones?

Sometimes following a special diet may be enough to prevent you from forming more kidney stones. Other times, medications, in addition to a special diet, may be needed. Please note that not all dietary recommendations benefit all types of stone formers.

What kind of diet will I have to follow?

You may be asked to make changes to the amount of salt (sodium), calcium, oxalate, protein, citrate, potassium and fluid in your diet. A registered dietitian can help you with making these changes.

My doctor told me to drink a lot of fluids. How much is “a lot”? Does it matter what kind of fluid I drink?

Staying well hydrated by drinking enough water is one of the best measures you can take to avoid kidney stones. To lessen your risk of forming a new stone, it is very important that you drink at least three quarts (12 cups) of fluid throughout the day. In hotter weather, you may need to drink more to make up for fluid loss from sweating. This will help keep your urine less concentrated. Less concentrated urine reduces the risk of stone formation. Most of the fluid you drink should be water. Try to drink a glass of water before bed and if you wake during the night to use the bathroom, drink another glass before going back to bed.

I had a calcium stone. What type of diet should I follow? Will I have to avoid high calcium foods?

Calcium is not the enemy. If you have high calcium in the urine then sodium reduction is helpful for stone prevention. Instead of reducing your calcium intake, focus on limiting the sodium in your diet and pair calcium-rich foods with oxalate-rich foods. Extra sodium causes you to lose more calcium in your urine, putting you at risk for developing another stone. Your doctor will probably advise you to limit sodium to 2,000 milligrams each day. There are many sources of “hidden” sodium such as canned or commercially processed foods as well as restaurant-prepared and fast foods. A dietitian helps you understand food labels and make changes in the amount of sodium that you eat. If you do not have high calcium in the urine then for stone reduction you might be better off focusing on other dietary changes. Your doctor or a registered dietitian can help determine if you need more or less calcium and help you plan a diet that is healthy.

I had an oxalate stone. What type of diet should I follow? Do I need to avoid foods high in oxalate?

Calcium oxalate kidney stones are the leading type of kidney stones. Oxalate is naturally found in many foods, including fruits and vegetables, nuts and seeds, grains, legumes, and even chocolate and tea. Some examples of foods that contain high levels of oxalate include peanuts, rhubarb, spinach, beets, chocolate and sweet potatoes. The oxalate content of food can vary due to differences in such things as soil quality and state of ripeness. There may be variation in published data, too, as different methods may be used to determine the oxalate content of food.

Some research suggests that limiting high oxalate foods may help reduce your chance of forming another oxalate stone. However, many high oxalate foods are healthful so it is wise to not overly restrict your diet if not necessary. Most kidney stones are formed when oxalate binds to calcium while urine is produced by the kidneys. New research indicates that eating and drinking calcium and oxalate-rich foods together during a meal is a better approach than limiting oxalate entirely because oxalate and calcium are more likely to bind to one another in the stomach and intestines before the kidneys begin processing, making it less likely that kidney stones will form.

Talk with your doctor about how strictly you need to avoid oxalate-containing foods.

I had a uric acid stone. What does that mean? What type of diet should I follow?

Another common type of kidney stone is a uric acid stone. Red meat and shellfish have high concentrations of a natural chemical compound known as a purine. High purine intake leads to a higher production of uric acid which then accumulates as crystals in the joints, or as stones in the kidneys.

To prevent uric acid stones, cut down on high-purine foods such as red meat, organ meats, and shellfish, and follow a healthy diet that contains mostly vegetables and fruits, whole grains, and low-fat dairy products. Limit sugar-sweetened foods and drinks, especially those that contain high fructose corn syrup. Limit alcohol because it can increase uric acid levels in the blood and avoid crash diets for the same reason. Eating less animal-based protein and eating more fruits and vegetables will help decrease urine acidity and this will help reduce the chance for stone formation.

You should also be sure to drink at least three quarts (12 cups) of water a day to help reduce the risk for stone formation. Making these healthy lifestyle changes can also help reduce your risk of developing gout because high uric acid is a leading risk factor for gout.

Is there anything else I can do with my diet to help prevent kidney stones?

Reducing the amount of animal protein may help. Sources of animal protein include beef, chicken, pork, fish and eggs. Most people need only four to six units of high protein foods and three servings of milk or cheese a day. Check with your doctor or dietitian to be sure your protein intake is enough, but not too much.

Chronic kidney stones are often treated with potassium citrate. Studies have shown that limeade, lemonade and other fruits and juices high in natural citrate may offer similar stone-preventing benefits. It is believed that citrate in the urine may prevent the calcium from binding with other constituents that lead to stones. Also, some evidence suggests that citrate may prevent crystals that are already present from binding with each other, thus preventing them from getting bigger. Please note that juices made from actual limes and lemons contain higher levels of citrate and beware of the sugar content in juices, because this can increase kidney stone risk.

Will it help/hurt me to take a vitamin or mineral supplement?

The B vitamins (which include thiamine, riboflavin, niacin, B6 and B12) have not been shown to be harmful to people with kidney stones. In fact, some studies have shown that B6 may actually help people with high urine oxalate. However, check with your doctor or dietitian for advice on the use of vitamin C, vitamin D, fish liver oils or mineral supplements containing calcium since some supplements can increase the chances of stone formation in some people.

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.

Specific dietary guidelines:

Fluid intake:-

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, 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 than 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.

SALT

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 contain 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, low sodium intake helps to control or prevent high blood pressure, which can lead to heart disease, stroke, heart failure, and kidney disease.

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

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 vegetables 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

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.

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