Oxalate is a naturally occurring molecule found in abundance in plants and humans. It’s not a required nutrient for people, and too much can lead to kidney stones.
In plants, oxalate helps to get rid of extra calcium by binding with it. That is why so many high-oxalate foods are from plants.
When we eat foods with oxalate, it travels through the digestive tract and passes out in the stool or urine.
As it passes through the intestines, oxalate can bind with calcium and be excreted in the stool. However, when too much oxalate continues through to the kidneys, it can lead to kidney stones.
Calcium oxalate kidney stones are the most common type of kidney stone in the U.S. The higher your levels of oxalate, the greater your risk of developing these kinds of kidney stones.
If you are at high risk for kidney stones, lowering the amount of oxalate that you eat may help reduce this risk.
However, recent research indicates that boosting your intake of calcium-rich foods when you eat foods that are high in oxalate may be a better approach than simply eliminating it from the diet.
As they digest, oxalate and calcium are more likely to bind together before they get to the kidneys, making it less likely that kidney stones will form.
Foods that are high in vitamin C can increase the body’s oxalate levels. Vitamin C converts to oxalate. Levels over 1,000 milligrams (mg) per day have been shown to increase oxalate levels.
Taking antibiotics, or having a history of digestive disease, can also increase the body’s oxalate levels. The good bacteria in the gut help get rid of oxalate, and when the levels of these bacteria are low, higher amounts of oxalate can be absorbed in the body.
Drinking enough fluid each day can help clear kidney stones or even keep them from forming. Spreading your intake of liquids throughout the day is ideal. Choosing water over other drinks is preferable.
Avoid eating too much animal protein, as this can cause stones to form.
Getting enough calcium is also helpful. Getting too little calcium can increase the amount of oxalate that gets to the kidneys, which will increase the risk of kidney stones.
Lowering your salt intake can also lower your risk of kidney stones. High-salt diets tend to cause more calcium to be lost in the urine. The more calcium and oxalate in the kidneys, the greater the risk of kidney stones.
Lists that provide the oxalate content in foods can be confusing. The oxalate levels reported in foods can vary depending on the following factors:
- when the foods are harvested
- where they are grown
- how their oxalate levels were tested
These foods should be avoided when lowering oxalate intake. Generally foods that contain 10 mg or more per serving are considered high oxalate foods. Oxalates are found in plants.
Foods that are highest in oxalate include:
High-oxalate fruits include:
- purple grapes
Vegetables that contain high levels of oxalate include:
- Swiss chard
To reduce how much oxalate you get, avoid:
- soy products
Some grain products are also high in oxalate, including:
- bran flakes
- wheat germ
The following foods are also high in oxalates:
It may seem that many foods contain oxalate, however, this does not mean that everything needs to be avoided.
With careful planning and a balanced diet with proper portion sizes, you can enjoy oxalate containing foods. It’s best to consult your doctor or dietitian to go over what you can and cannot consume to fit your needs.
Dairy contains no oxalate; however, watch for sodium content (think cheese) and chocolate/cacao (they contain oxalate).
Increasing your calcium intake when eating foods with oxalate can help lower oxalate levels in the urine. Choose high-calcium dairy foods such as milk, yogurt, and cheese.
Vegetables can also provide a good amount of calcium. Choose among the following foods to increase your calcium levels:
High-calcium legumes that have a fair amount of calcium include:
- kidney beans
- baked beans
- navy beans
Fish with a lot of calcium include:
- sardines with bones
Meats are safe to eat as they do not contain oxalate. However, eating large portions can increase the risk of kidney stones. Keep proper portion sizes in mind, 2-3 servings a day, or 4 to 6 ounces.
To lower your risk of kidney stones, add a high-calcium food to a meal that contains a food with higher levels of oxalate. It’s more important to focus on pairing a high-oxalate food with a high-calcium food, and then to look at the nutrients individually.
Some foods will be both moderately high in calcium and high in oxalate, so adding a second source of calcium may be warranted.
For example, if you add wheat germ to your oatmeal, be sure to add some milk.
If you’re cooking spinach, don’t feel guilty about combining it with pizza or lasagna. If you have a craving for a berry smoothie, add some regular or Greek yogurt to help provide balance.