It's no secret that foods like spinach, broccoli and sweet potatoes are packed with health benefits. But did you know that they also contain a lot of oxalates?
Oxalates are organic compounds that can build up in the kidneys, increasing the risk of painful kidney stones. But while a low-oxalate diet was once the best treatment for kidney stones, new research now suggests that it may not be necessary to cut oxalates from your diet altogether.
So what are oxalates, how can they affect your health, and should you really cut back on your intake? Here's what you need to know.
What are oxalates?
Oxalates, also called oxalic acid, are a natural compound found in various food sources. Some of the most common oxalates in food are found in plant sources such as fruits, vegetables, nuts and seeds. Oxalate can also be produced naturally by your own body.
Oxalates often bind to minerals such as calcium and are excreted from the body through feces. However, large amounts of oxalate can build up in the kidneys, leading to the formation of kidney stones.
Kidney stones form when hard mineral deposits form in the inner lining of the kidneys, causing symptoms such as stomach pain, nausea and vomiting. Although there are several types of kidney stones, calcium oxalate stones are considered one of the most common.
A traditional kidney stone diet involves limiting the consumption of oxalate foods to prevent the formation of these painful mineral deposits. However, many oxalate foods are also rich in other nutrients and often double as fiber-rich, magnesium-rich foods.
Rather than cutting these foods out of your diet altogether, recent research has found that increasing your calcium intake may be just as effective for kidney stone prevention.
Are oxalates bad for you?
Oxalates are considered an antinutrient, meaning they can bind to certain minerals in the body and prevent their absorption. Calcium in particular binds to oxalate and is excreted from the body, which can be problematic for those who consume a diet high in oxalate and low in calcium.
However, most research generally suggests that consuming high-oxalate foods in moderation as part of a healthy diet is unlikely to have adverse health effects. Additionally, soaking or cooking foods can significantly reduce oxalate levels to maximize nutrient absorption.
Kidney stones are another common problem linked to oxalate consumption. This is because large amounts of oxalates can build up in the kidneys, which can contribute to the formation of kidney stones.
Although reducing your intake of foods high in oxalate may help reduce the risk of kidney stones, many of these foods are rich in other important vitamins and minerals that your body needs.
Additionally, studies show that combining oxalate foods with calcium-rich foods could promote the excretion of oxalate from the body, without having to remove oxalate-rich foods from your refrigerator.
Foods high in oxalate
Oxalates are found in varying amounts in most plant foods, including many fruits, vegetables, nuts and seeds. Meanwhile, most animal products such as meat, fish and poultry contain only trace amounts of oxalates.
Here are some of the best foods high in oxalates:
- Fruits: blackberries, blueberries, raspberries, kiwis, tangerines, figs
- Vegetables: broccoli, rhubarb, okra, leek, beets, potatoes, eggplant, sweet potatoes, zucchini, carrots, celery, olives, kohlrabi, chicory parsley, bell pepper
- Leafy vegetables: spinach, endive, beet greens, kale, kale, chard
- Nuts and seeds: almonds, cashew nuts, peanuts, sesame seeds
- Legumes and soy products: miso, tofu, soy milk, green beans and kidney beans
- Cereals: bulgur, corn grits, wheat germ, whole wheat bread, amaranth, buckwheat and quinoa
- Drinks: cocoa/chocolate, chocolate milk, black tea, instant coffee, dark beers
Some foods also contain moderate amounts of oxalates and can be included in a low-oxalate diet. Here are a few medium-oxalate foods:
- Fruits: apples, oranges, plums, pears, pineapple, peaches, apricots
- Vegetables: artichoke, fennel, canned peas, asparagus, tomato, lima beans, Brussels sprouts, mustard greens, turnips, onions, parsnips, corn
- Drinks: brewed coffee, carrot juice, tomato juice, orange juice
Low oxalate diet
If you want to learn how to prevent kidney stones, a low-oxalate diet is often recommended, especially if you are prone to kidney stones.
A low oxalate diet typically provides less than 40-50 milligrams of oxalates per day. In addition to limiting your oxalate intake, staying well hydrated, moderating your protein intake and increasing calcium consumption are other important aspects of a low-oxalate diet. It is normally recommended to follow the diet for at least 3 to 6 weeks to see if your symptoms improve.
Here are a few simple steps for following a low-oxalate diet:
1. Moderate consumption of foods high in oxalate
Minimizing your intake of high-oxalate foods from the list above may help prevent kidney stones.
However, it is not necessary to completely eliminate these foods from your diet. Recent research even suggests that increasing your calcium intake could boost oxalate excretion and possibly be more effective against kidney stones.
2. Enjoy a variety of low-oxalate foods
There are plenty of nutrient-rich, low-oxalate foods that you can enjoy as part of a healthy, well-rounded diet. Some of the best foods to include in a low-oxalate diet include:
- Fruits: bananas, cherries, mangoes, grapefruit, melons, grapes, nectarines, papaya
- Vegetables: cauliflower, kohlrabi, radish, chives, mushrooms, cucumbers, cabbage, peas, avocados
- Protein: meat, poultry, seafood and eggs
- Dairy products: milk, cheese, yogurt, butter
- Cereals: rice, corn bran, rye bread, egg noodles
- Drinks: water, herbal tea, wine
- Herbs and spices: rosemary, oregano, basil, turmeric, ginger, dill
3. Increase your intake of calcium-rich foods
Oxalate and calcium bind together, which can help prevent them from forming kidney stones. Therefore, it is recommended to combine oxalate foods with foods high in calcium, including sardines, yogurt, kefir, cheese and almonds.
Ideally, you should aim for 2-3 servings of calcium-rich foods per day.
4. Drink plenty of water
Water can help flush substances from the kidneys and thus help protect against kidney stones. To stay well hydrated, try to drink at least eight glasses of water or liquids per day.
5. Moderate protein intake
Eating too much animal protein can contribute to the formation of kidney stones. A healthy diet should provide between 10 and 35 percent of total daily calories from protein, which can come from sources such as meat, fish and poultry, as well as legumes, nuts and seeds.
6. Cook/soak oxalate foods
Boiling and steaming can help reduce oxalate levels in some foods, including greens and other vegetables. Try boiling vegetables for 6-10 minutes or steaming them for several minutes until soft.
Soaking grains and legumes can also help reduce oxalate levels while minimizing levels of other antinutrients such as phytate, protease inhibitors, lectins and tannins. For help with soaking and sprouting food, check out this handy sprouting guide.
7. Try supplementation
Some people choose to take calcium citrate, NAG (N-Acetyl-Glucosamine), CMO (cetyl myristoleate), or a combination of these supplements to deal with oxalic acid-related side effects or pain.
To manage your symptoms, ask your healthcare provider if these may be helpful to you.
Final thoughts
- Oxalates are natural compounds found in a variety of plant foods, including many fruits, vegetables, nuts and seeds.
- In large amounts, oxalates can build up in the kidneys, causing kidney stones.
- Although following a low-oxalate diet was once recommended to prevent kidney stones, recent research suggests that eating more calcium-rich foods to increase oxalate excretion may be more effective.
- It may also be helpful to enjoy a variety of low-oxalate foods, drink plenty of water, cook or soak oxalate foods, and limit animal protein intake.
