Oxalates, also called oxalic acid, are compounds that naturally occur in plants. When you eat plants, you take in oxalates. Your body make oxalates as well.
Foods high in oxalates include spinach, almonds, peanuts, chocolate, whole-wheat bread and tofu. Although these foods provide beneficial nutrients, the oxalates can bind to minerals like calcium. Although most folks can discard these compounds in their urine, the accumulation of these compounds can result in calcium oxalate kidney stones, the most common type of kidney stone.
If you are prone to kidney stones, your doctor or registered dietitian nutritionist may recommend following a low oxalate diet. In this article you will find information about a low oxalate diet, how a high oxalate diet can lead to kidney stones, tips for eating a low oxalate diet and steps to take to help avoid kidney stones.
What Is a Low Oxalate Diet?
Oxalate is a natural substance found in many common foods in your diet, many of which are healthy foods. As your body uses food for energy, waste products travel through the blood to the kidneys and are removed from the body in the form of urine. If you have too much waste that needs to pass through the urine and not enough liquid to carry it out, crystals begin to form. These crystals stick together and create a stone (or a mass). Oxalate is one substance that can form into crystals in the urine. This can happen several ways: if there is too much oxalate, too little liquid and if the oxalate sticks to the calcium while the urine is being made by the kidneys.
“A typical diet is estimated to have about 200 to 300 mg of oxalate per day,” explains Christy Wilson, a Tucson, Arizona-based dietitian and owner of Christy Wilson Nutrition. A low oxalate diet is typically defined as under 100 mg to 50 mg per day.
There are certain risk factors that may increase your chances of forming calcium oxalate stones. According to the National Kidney Foundation, these risk factors include:
— Dehydration from not drinking enough fluids.
— A diet that is too high in protein, oxalate, sodium (salt) and added sugar.
— Having obesity.
— Medical conditions like dent disease (a rare genetic disorder that affects the kidneys) and hyperparathyroidism.
— Digestive diseases like inflammatory bowel disease, ulcerative colitis and Crohn’s disease.
— Having had gastric bypass surgery.
If your calcium oxalate stones keep returning, your healthcare provide may choose to test you for any of the above conditions. Your healthcare provider may also examine your lifestyle to see if there are any modifiable risk factors to help lower your risk of forming calcium oxalate stones.
[READ: Kidney Function Tests: Purpose, Types and Procedure.]
What Is a Kidney Stone?
Typically oxalate and calcium bind together in the intestines and are excreted together in your stool. If there is not enough calcium in your diet, the extra oxalate has nothing in the intestines to bind to, so it ends up in your kidneys, which excrete it in the urine.
A calcium oxalate kidney stone forms when crystals of oxalate in your kidneys stick together and form a stone (or a mass). This can happen when you have too much waste that needs to be passed through the urine but not enough liquid to carry it out.
[SEE: 10 Symptoms of a Kidney Problem.]
Does Too Much Oxalate Lead to Kidney Stones?
Although moderating intake of high oxalate foods is recommended for folks who tend to get calcium oxalate stones, this dietary change alone isn’t the most beneficial. Typically, kidney stones are formed when oxalate binds to calcium while urine is produced by the kidneys. That is why the most effective solution is to consume calcium and oxalate foods together during a meal.
[SEE: 8 Calcium-Rich, Nondairy Foods.]
What Causes Oxalate Levels to Increase?
There are other factors that can contribute to high oxalate levels in the urine. Vitamin C supplements can cause high amounts of oxalate in the urine. A 2022 published study looked at over 23,000 Swedish men taking vitamin C supplements over an 11-year period. The results found that men who reported taking vitamin C supplements were twice as likely to have kidney stones. It should be noted that the increased risk is associated with vitamin C supplementation, and not through diet. If you are at a high risk for calcium oxalate kidney stones, speak with a healthcare provider before taking vitamin C supplements.
Another factor that can contribute to high oxalate levels are antibiotics, which can decrease the beneficial bacteria in your gut that help break down oxalates. This can lead to oxalate buildup. Other medications that can lead to increased oxalate levels include protease inhibitors, some diuretics and calcium-based antacids. Speak with your healthcare provider if you have any concerns.
[Read: How to Prevent Kidney Stones and Improve Kidney Health: Foods to Eat and Avoid]
Can a Low Oxalate Diet Prevent Kidney Stones?
The most common type of kidney stones is calcium oxalate kidney stones, when calcium combines with oxalates in the urine. However, another common type is uric acid kidney stones. This is caused by high purine intake which leads to monosodium urate production. Two lesser common kidney stones include struvite which is caused by infections in the upper urinary tract and cysteine which is rare and tend to run in families with a history of cystinuria (an amino acid which accumulates in the urine).
If you’re at risk for calcium oxalate kidney stones, Mascha Davis, registered dietitian nutritionist and author of “Eat Your Vitamins,” says that many factors like dehydration or certain health conditions (mentioned above) can determine if someone is susceptible for developing kidney stones.
In addition, a diet high in oxalates can also be a factor. The National Kidney Foundation suggests not cutting out all oxalate-containing foods, but rather eating less of these foods to decrease the chance of new stones from forming. In addition, the consumption of calcium during a meal with oxalate-containing foods along with maintaining proper hydration as recommended by a published 2019 paper on dietary oxalates and kidney stone formation.
How to Decrease Oxalate Levels
If you are at risk for the development of calcium oxalate kidney stones, the following is recommended in order to decrease oxalate levels.
Increase fluid intake
According to Wilson, “this may be the easiest and most effective way to avoid developing kidney stones.”
Increasing your fluids helps thin out your urine and makes it tougher for chemicals to build up and form crystals. Consult your healthcare provider for the amount of fluids that are recommended for you.
Avoid eating too much protein
Too much protein can lead to calcium oxalate stones to form, according to the National Kidney Foundation.
Lessen salt (sodium) intake
A diet that is high in sodium can cause calcium to build up in your urine. Having too much calcium in your urine can potentially cause new stones to form.
Consume calcium-rich foods
Calcium is found in milk and dairy foods like cheese and yogurt. It’s recommended to eat foods high in calcium over taking a supplement. Speak to a registered dietitian nutritionist to help find the best sources of calcium in your diet. Too much or too little calcium can lead to the formation of calcium oxalate kidney stones.
The National Kidney Foundation recommends consuming three servings of milk and dairy foods — one serving at each meal. However, a RDN will to look at your urine, blood tests and medical conditions before making a final recommendation that is customized to you and your needs. The following are calcium-rich foods that are recommended on a low-oxalate diet:
— Whole, reduced fat, low fat, and skim milk.
— Plain yogurt or with allowed fruit like cherry, peach, banana and mango.
— Soy, almond and rice beverages fortified with calcium.
— Sardines with soft bones.
— Plain soy-based yogurt or with allowed fruit cherry, peach, banana and mango.
— Cheese.
— Kefir.
— Lentils and beans.
Avoid vitamin C supplements
Too much vitamin C can lead to high oxalate levels in the urine, which can increase the risk of stone formation. Speak with your healthcare provider before taking a vitamin C supplement.
Consume less oxalate-rich foods
Although most oxalate-rich foods are nutrient-rich, the National Kidney Foundation recommends limiting how many oxalate-rich foods you eat daily. Foods with high oxalate levels that should be avoided include nuts, rhubarb, beets, chocolate soy milk, All Bran cereal, buckwheat flour, miso, tahini, sesame seeds, and Swiss chard.
Low Oxalate Foods
The following are low-oxalate foods:
Vegetables
— Asparagus.
— Broccoli.
— Carrots.
— Sweet or white corn.
— Peeled cucumber.
— Canned green peas.
— Lettuce.
— Lima beans.
— Parsnips.
— Tomatoes or tomato juice.
— Turnips.
— Brussel sprouts.
— Cauliflower.
— Cabbage.
— Mushrooms.
— Onions.
— Green peas.
— White potatoes.
— Radishes.
Fruits
— Avocado.
— Apple.
— Apricots.
— Red sour cherries.
— Cranberry juice.
— Grape juice.
— Orange (no peel) and orange juice.
— Peaches.
— Pears.
— Pineapple and pineapple juice.
— Plums.
— Prunes.
— Apple juice
— Banana.
— Mango.
— Melons including cantaloupe, cassava, honeydew, watermelon.
— Nectarines.
— Peaches.
Proteins
— Eggs.
— Beef, lamb, pork.
— Chicken and turkey
— Fish and shellfish.
— Beans.
— Cheese.
— Lentils.
— Kefir.
Starches
— Rice.
— Quinoa.
— All bread.
— All pasta.
Beverages
— Coffee.
— Bottled beer.
— Carbonated soda.
— Distilled alcohol.
— Lemonade.
— Wine.
— Buttermilk.
— Whole, reduced fat, low fat and skim milk.
— Plain yogurt or with allowable fruit.
— Soy, almond and rice beverages.
— Plain soy yogurt or with allowable fruit.
Other foods
— Black pepper.
— Sugar.
— Lemon and lime juice.
— Bacon.
— Mayonnaise.
— Butter.
— Margarine.
— Coconut.
— Jelly or preserves made with allowable fruits.
High Oxalate Foods to Avoid
The following are high oxalate foods that the National Kidney Foundation recommends to avoid:
Vegetables
— Beets including tops, roots and greens.
— Collards.
— Kale.
— Leeks.
— Mustard greens.
— Okra.
— Parsley
— Sweet potato
— Rutabagas
— Spinach
— Swiss chard
— Watercress
Fruits
— Red currants.
— Dewberries.
— Purple grapes.
— Gooseberries.
— Lemon peel.
— Lime peel.
— Orange peel.
— Rhubarb.
Proteins
— Peanut butter.
— Nuts like almonds, pecans, cashews.
— Tofu (if it is processed with calcium, then it is allowable in a small amount).
Starches
— Soybean crackers.
— Wheat germ.
— Fruit cake.
Beverages
— Draft beer.
— Ovaltine.
— Cocoa and chocolate beverages.
Other foods
— Chocolate.
When to See a Doctor
Signs and symptoms of kidney stones include severe pains in either side of your lower back, a stomach ache or vague pain that doesn’t go away, blood in the urine, nausea, vomiting, fever, chills and urine that smells bad or is cloudy. If you have any of these symptoms or are concerned, see you healthcare provider immediately.
Measurement of oxalate
In order to diagnose kidney stones, your physician will ask for a medical history, will most likely do a physical exam and imaging testing, and urine and blood tests. Image testing is done so your physician can know the exact shape and size of the stone. It can be done with high resolution CT scan, KUB x-ray or intravenous pyelogram.
The healthcare provider may also request a collection of 24-hour urine to test for levels of stone-forming minerals and stone-preventing substances. A blood test can check for calcium, phosphorus, and uric acid levels. In addition, a stone analysis is performed if a stone comes out of your body in order to determine the cause and plan to prevent it from happening again.
You healthcare provider will determine how often to collect urine samples in order to check how well limiting the amount of oxalate in your food is working.
Bottom Line
Calcium oxalate kidney stones can happen, but keeping hydrated and going to annual physicals is essential to keep on top of your health.
If you are at risk for calcium oxalate kidney stones or have been diagnosed with calcium oxalate kidney stones, then avoiding high oxalate foods while consuming lower oxalate foods together with high calcium foods is recommended.
Also, proper hydration, monitoring salt and protein intake also play a role in helping to keep symptoms at bay and decrease the change of the recurrence of stones. The proper diet for folks at high risk or diagnosed with kidney stones is rather individual, so it is best to consult with a healthcare professional to tailor the plan of action for you.
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Low Oxalate Diet: Can It Prevent Kidney Stones? originally appeared on usnews.com
