What is oxalate?
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. In humans, it may work as a “prebiotic,” feeding good bacteria in the gut.
How does the body process it?
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 North America. The higher your levels of oxalate, the greater your risk of developing these kinds of kidney stones.
What is a low-oxalate diet?
If you are at high risk for kidney stones, lowering the amount of oxalate that you eat may help reduce this risk.
However, new 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.
What causes oxalate buildup?
Foods that are high in vitamin C can increase the body’s oxalate levels. Vitamin C converts to oxalate, and 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.
What can reduce oxalate?
Drinking enough fluid each day can help clear kidney stones or even keep them from forming. Spreading liquids throughout the day is ideal. Choosing water over other drinks is preferable.
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.
How is oxalate measured?
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
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, minimize consumption of:
- soy products
Some grain products are also high in oxalate, including:
- bran flakes
- wheat germ
The following foods are also high in oxalates:
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 high in calcium include:
- sardines with bones
How to avoid kidney stones
To lower your risk of kidney stones, add a high-calcium food to a meal that contains a food with higher levels of oxalate.
For example, if you add wheat germ to your oatmeal, be sure to add some milk as well. If you are 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.
- Assimos, D. (2004). Vitamin C supplementation and urinary oxalate excretion. Reviews in Urology, 6(3), 167. Retrieved from ncbi.nlm.nih.gov/pmc/articles/PMC1472830/
- Diet and kidney stones. (n.d.) kidney.org/atoz/content/diet
- Mayo Clinic Staff. (2015, February 26). Kidney stones. Retrieved from mayoclinic.org/diseases-conditions/kidney-stones/basics/definition/con-20024829
- Your guide to a low oxalate diet. (2016). Retrieved from litholink.com/sites/default/files/LowOxalateDietBro_DRAFT1.pdf