About 1 million Americans get kidney stones every year. Kidney stones can put you at risk for loss of renal function. Depending on the type of kidney stone, limiting certain foods, including those high in oxalates or containing uric-acid forming purines, can help lower your chances of recurring stones.
What Are Oxalates?
Oxalates are natural substances contained in many foods, including fruits and vegetables, nuts and seeds, grains, legumes and even chocolate and tea. Oxalates bind to calcium during digestion and normally leave the body in your stool. If oxalates are not bound to calcium, they travel as waste to your kidneys where they typically leave the body in the urine.
However, if there are too many oxalates and other crystal-forming substances, which can include calcium and uric acid, and not enough fluid in the urine, the result is the creation of mineral and salt fragments that can stick together. These fragments can eventually form a larger hard crystal known as a kidney stone, according to the National Kidney Foundation.
Eating foods containing oxalates is not a concern if you are healthy and do not have a history of kidney stones or already have a kidney stone. A report in the journal of Clinical Nutrition Research in July 2015 determined that it's safe to eat food containing oxalates and often helpful for anyone with diabetes, hypertension or high blood cholesterol. However, the report emphasizes that patients with developed kidney stones should change to a low-oxalate diet.
Symptoms of Kidney Stones
If you have a kidney stone you may not notice any symptoms until the stone moves around in your kidney or passes from your kidney to your bladder. When this happens, you may experience some symptoms such as:
- Severe pain in your side and back, below the ribs
- Pain radiating to the lower abdomen and groin
- Fluctuation in intensity of pain
- Pain on urination
- Pink, red, brown, cloudy or foul-smelling urine
- Nausea and vomiting
- Persistent need to urinate or urinating small amounts more often
- Fever and chills indicating an infection
Small kidney stones often pass through your system on their own. To encourage this, drink at least six to eight glasses of water per day to produce a large amount of urine.
Types of Kidney Stones
While most kidney stones are formed as a result of oxalates, some are formed from excessive uric acid. Some less-common types may contain different mineral salts. Knowing which type of kidney stone you have can help determine your treatment options and how to prevent the risk of getting another stone.
If you already have a kidney stone, try to save it after passing and take it to your doctor for analysis. Modifying your diet and eliminating certain foods is one of the key factors to treat and reduce stone formation.
The two main types of kidney stones are: calcium stones, specifically calcium oxalate stones and uric acid stones.
Calcium Oxalate Stones
Calcium oxalate stones are the most common type of kidney stone and are most likely to form in men between the ages of 20 and 30. As the name implies, the stones consist of calcium and oxalates. Since oxalates are present in certain foods, a modified meal plan that includes a low-oxalate diet may help to clear kidney stones or prevent them from forming.
It is important that you increase your calcium when eating an oxalate-restricted diet. A low intake of calcium can raise oxalates and may increase your chances of forming calcium oxalate kidney stones. Including calcium-rich foods in your low-oxalate diet helps reduce the amount of oxalate absorbed by your body. Strive for the recommended daily amount of calcium — 1,000 milligrams for adults — from dairy foods or other calcium-rich foods.
If you are on a low-oxalate diet, consuming less than 100 milligrams of oxalates is good but less than 50 milligrams daily is ideal. Typical diets contain upward of 200 to 300 milligrams of oxalate from food.
According to a chart compiled by University of Chicago, some food groups that contain the highest amount of oxalates that you should try to avoid or limit include:
Fruits: Raspberries have the highest oxalate content of fruits with 48 milligrams per cup but oranges, dates, avocado, kiwi and grapefruit are high in oxalate and should be consumed with caution. Some canned fruit, including pineapple, should be avoided. Some dried fruit, especially figs, pineapple and prunes have a lot of oxalate. For example a half-cup of dried pineapple contains 30 milligrams.
Vegetables: Spinach and rhubarb have the highest oxalate content of vegetables. Potatoes are not ideal for preventing stone formations. Also be aware of tomato sauce, turnips, okra, and yams and beans. Choose salad vegetables instead – they have almost no oxalate.
Pasta, rice and grains: Stay away from buckwheat groats — one cup cooked has 133 milligrams of oxalate. Other grains with a high content include corn grits, rice bran, cornmeal, bulgur, brown rice flour, millet and wheat berries.
Nuts and seeds: Most nuts are very high in oxalates. And it's easy to eat a lot of them in one sitting. Limit your consumption of almonds, mixed nuts, walnuts, peanuts and cashews.
Desserts: When satisfying your sugar cravings, moderate your portion size when eating chocolate syrup, brownies, fudge sauce and cake.
Beverages: A cup of hot chocolate contains 65 milligrams and carrot juice has 27 milligrams of oxalates per cup. The longer you steep your tea, the more oxalate it will have. However, coffee contains no oxalate.
Uric Acid Stones and Gout
Uric acid stones are another type of kidney stone that is common. It can form if your urine is too acidic. Gout, a painful arthritic condition, is a well-established risk factor for uric acid stone formation.
A study in the American Journal of Kidney Diseases that was published in August 2017 reported the results of a previous study concluding that a history of gout may double the risk for forming kidney stones. Symptoms of gout often exhibit low urine pH levels, which increases the concentration of uric acid.
Uric acid is naturally produced as a waste byproduct from digestion of protein, which contain purines. Typically, your body filters out uric acid through your kidneys and then excretes it in urine. Concentrations of uric acid can result if your body is unable to excrete uric acid fast enough and deposits build up in your blood, kidneys or joints.
An excessive intake of foods containing purine can lead to a higher production of uric acid and result in a larger acid load for your kidneys to excrete. A high concentration of acid can make it easier for uric acid stones to form. If you have a predisposition to uric acid kidney stones or gout, you should limit foods that contain purines.
- Fish, seafood and shellfish: anchovies, sardines, herring, mussels, codfish, scallops, trout and haddock
- Meat: bacon, turkey, veal, venison and organ meats like liver
- Beverages: all types alcohol.
- Sugary drinks such as soda, and sugary foods, especially with high fructose corn syrup
Foods that contain a moderate level of purines are:
- Meat: beef, chicken, duck, pork and ham
- Shellfish: crab, lobster, oysters and shrimp
- High-purine vegetables: According to a study, published in January 2014 in Annals of the Rheumatic Diseases, vegetables high in purines, such as asparagus and spinach, don't increase the risk of gout or recurring gout flares.
- UPMC Nutrition Services: "Low Oxalate Diet"
- Advances in Urology: "Kidney Stone Disease: An Update on Current Concepts"
- National Kidney Foundation: "6 Easy Ways to Prevent Kidney Stones"
- National Kidney Foundation: "What Are Oxalates and Why are They a Concern for Kidney Disease Patients?"
- Clinical Nutrition Research: "Nutritional Management of Kidney Stones (Nephrolithiasis)"
- Mayo Clinic: "Kidney Stones"
- Wake Forest Baptist Health: "Kidney Stones"
- Health.gov: "Dietary Guidelines for Americans, 2015-2020: Appendix 7. "Daily Nutritional Goals for Age-Sex Groups Based on Dietary Reference Intakes and Dietary Guidelines Recommendations"
- University of Chicago: "How to Eat a Low Oxalate Diet"
- University of Chicago: "The 179 High Oxalate Foods and Products"
- American Journal of Kidney Diseases: "Serum Uric Acid and Risk of Kidney Stones"
- International Kidney Stone Institute: "Uric Acid Stones"
- Arthritis Foundation: "Safe Foods for Gout"
- American Kidney Fund: "Foods and Drinks to Avoid When You Have Gout"
- Annals of the Rheumatic Diseases: "Purine-Rich Foods Intake and Recurrent Gout Attacks"