Oxalate — or oxalic acid — is a natural component of many plant foods.
Oxalate is generally harmless for most people, but others — especially those with kidney stones — can benefit from a low-oxalate diet.
This article explains what to eat and avoid on a low-oxalate diet and for which conditions the diet may be beneficial.
What is oxalate?
Oxalate is a molecule naturally found in many plant foods, including vegetables, fruits, grains, beans, and nuts.
The function of oxalate in plants is unclear, but it’s thought to be involved in seed germination, calcium storage and regulation, structural strength, and insect repulsion (1).
In contrast to plants, oxalate has no known function in humans (2).
However, the body can produce oxalate from the breakdown of vitamin C and the metabolism of certain amino acids — the building blocks of protein (3).
You can absorb around 10–15% of oxalate from foods, but other factors increase its absorption (2).
Low-calcium diets, for example, have been shown to increase oxalate absorption. This is because calcium binds to oxalate in the intestines and reduces its absorption, so without adequate calcium, your body absorbs more oxalate.
Conditions that decrease the absorption of fat like inflammatory bowel disease or procedures like gastric bypass can also increase oxalate absorption (3).
When improperly absorbed, fat binds to calcium, preventing calcium from binding oxalate and reducing its absorption.
The more oxalate your body absorbs, the more oxalate you excrete through your kidneys in urine.
As such, following a low-oxalate diet can reduce how much oxalate your body excretes through urine, which can help protect against kidney stones and may offer benefits for other conditions.
Foods to limit and eat
A low-oxalate diet includes primarily foods and drinks that contain low to moderate amounts of oxalate and limits those high in oxalate.
Foods to limit
- Vegetables: beets, cauliflower, celery, potatoes, rhubarb, spinach, swiss chard
- Fruits: oranges and raspberries
- Cereals and grains: amaranth, cornmeal, rice bran, tofu, and whole-grain flour
- Legumes: beans, boiled lentils, raw peas, and soybeans
- Nuts and seeds: almonds, hazelnuts, peanuts, and pistachios
- Chocolate and cocoa
Since the breakdown of vitamin C in your body produces oxalate, high intakes of the vitamin have been linked with an increased risk of kidney stones, particularly in men (6).
However, it’s unclear whether limiting vitamin C-rich foods is beneficial for reducing the risk of kidney stones based on the amount of vitamin C most people consume.
In either case, it may be wise to avoid vitamin C supplements, unless your doctor recommends one (7).
Foods to eat
Many foods are low in oxalates, allowing you to enjoy a varied diet.
Here are foods to eat on a low-oxalate diet:
- Fruits: apples, apricots, bananas, blueberries, cherries, grapes, nectarines, pears, watermelon
- Vegetables: artichokes, asparagus, broccoli, brussels sprouts, cauliflower, leeks, onions, zucchini
- Grains: corn flour, oats, popcorn, white rice
- Proteins: eggs, fish, poultry, meats
- Dairy: butter, cheese, milk, yogurt
- Beverages: coffee, fruit juice, and water
Because calcium binds to oxalate in the intestines and reduces its absorption, you should make sure to include plenty of calcium-rich foods and beverages in your diet.
The best sources of calcium are dairy products like yogurt, milk, and cottage cheese.
If you’re a vegan or lactose intolerant, many vegetables, including turnip greens, kale, and bok choy contain calcium.
A calcium supplement can help you meet your needs if you can’t get enough through diet alone.
Sample low oxalate diet
Here’s a one-day sample low oxalate diet menu rich in calcium:
- Breakfast: scrambled eggs, oatmeal cooked with milk, and black coffee
- Snack: Greek yogurt with blueberries and granola
- Lunch: turkey breast sandwich with cheese on white bread and a tossed salad
- Snack: apple slices and mozzarella cheese sticks
- Dinner: baked salmon, white rice, and parmesan-roasted broccoli
A low-oxalate diet for kidney stones
There are various types of kidney stones, but calcium oxalate stones are the most common (8).
These stones can occur due to high levels of oxalate in the urine, which may be caused by a genetic disorder, an intestinal disease, or consuming too much oxalate from foods (2).
Following a low oxalate diet reduces the excretion of oxalate in the urine and can therefore help prevent kidney stones.
Increasing your intake of calcium also reduces the absorption of oxalate and helps protect against kidney stones.
However, it’s unclear whether a higher excretion of oxalate contributes to kidney function decline or if it’s a consequence of kidney function decline.
Although a low-oxalate diet is primarily used to prevent kidney stones, it may be beneficial for other conditions.
Vulvodynia is a condition that causes chronic pain or discomfort of the vulva — the outer part of the female genitals (10).
Treatments for vulvodynia vary in effectiveness but focus on alleviating pain and discomfort.
Treatment options include medications, physical therapy, and eliminating things like certain soaps or creams that may irritate the vulva.
Too much oxalate in the urine is also believed to irritate the vulva and contribute to pain or discomfort.
As such, a low-oxalate diet may be beneficial with vulvodynia.
In one study, 14 of 59 women with vulvodynia who followed a low-oxalate diet and supplemented with calcium for three months reported pain relief, and of those 14 women, 6 could have pain-free sex (11).
Still, there’s limited research on the effectiveness of a low oxalate diet for vulvodynia, but it may be worth trying if other treatments haven’t offered relief.
Lichen sclerosus is a chronic inflammatory skin disorder that causes the skin around the genital and anal areas to become thin, whitened, and wrinkled (12).
The inflammation from the condition can also cause itching and pain, symptoms that are commonly treated with corticosteroid ointments and creams.
Although there is little-to-no research on the impact of diet on lichen sclerosus, following a low-oxalate diet is also believed to offer symptom relief by reducing inflammation and irritation around the affected areas — similar to vulvodynia.
Symptoms of IC can include painful urination, frequent urination at night, loss of bladder control, and pain during sex.
Although the best diet treatment for IC is an elimination diet, a low-oxalate diet has been suggested to reduce bladder irritation and relieve symptoms.
However, many oxalate-rich foods like spinach, potatoes, and nuts tend not to trigger IC symptoms according to some research (14).
In either case, you may choose to eliminate oxalate-rich foods and reintroduce them to determine whether they contribute to bladder irritation.
The bottom line
A low-oxalate diet limits oxalate-rich foods like spinach, whole grains, rhubarb, and beets.
Increasing your intake of calcium on a low-oxalate diet helps reduce oxalate absorption and excretion in the urine.
A low oxalate diet is primarily used to prevent kidney stones, but it may also offer symptom relief in people with vulvodynia, lichen sclerosus, and IC.