Scientists once thought that the greater the oxalate level in a food, the more likely it was to increase the risk of forming a kidney stone. However, researchers have discovered that consumption of only certain oxalate-containing foods is likely to significantly increase urinary oxalate.
The foods reported by at least one group of researchers to cause a significant increase in urinary oxalate include:
- spinach
- rhubarb
- beets
- nuts
- chocolate
- wheat bran
- strawberries
- peanuts
- almonds
- tea (Not every study has found tea to significantly increase urinary oxalate.)
There remains no universal consensus on which oxalate-containg foods belong on this list. Nonetheless, there is a growing awareness that the important issue for people with a history of kidney stone formation is to avoid certain high-oxalate foods—those that are most responsible for increasing urinary levels of oxalate.
To avoid oxalate ask about ingredients at restaurants and others’ homes, and read food labels. The following list is not complete. Consult with a healthcare professional before making any significant changes to your diet.
These foods are high in oxalate (greater than 10 mg per serving):
- Beans in tomato sauce
- Beer
- Beets
- Blackberries
- Black and red raspberries
- Blueberries
- Celery
- Chard
- Chocolate
- Cocoa
- Coffee powder (Nescafe)
- Collards
- Concord grapes
- Crackers made from soy flour
- Currants
- Dandelion greens
- Eggplant
- Escarole
- Fruit cake
- Fruit salad (canned)
- Green bell pepper
- Grits (white corn)
- Juices containing berries
- Kale
- Leeks
- Lemon and lime peel
- Nuts (especially peanuts and pecans)
- Okra
- Ovaltine
- Parsley
- Pokeweed
- Rhubarb
- Rutabagas
- Soy (see below)
- Spinach
- Strawberries
- Summer squash
- Sweet potatoes
- Tea
- Tofu
- Tomato soup
- Wheat germ
These foods are moderately high in oxalate (2–10 mg per serving):
- Apple
- Apricots
- Asparagus
- Bottled beer (12 oz limit/day)
- Broccoli
- Carrots
- Chicken noodle soup (dried)
- Coffee (8 oz )
- Cola beverage (12 oz limit per day)
- Corn
- Cornbread
- Cucumber
- Lettuce
- Lima beans
- Marmalade
- Oranges
- Orange juice (4 oz tsp grams] per day)
- Pineapple
- Plums
- Prunes
- Sardines
- Soy products (most)
- Sponge cake
- Tomatoes
- Tomato juice (4 oz kidney stones in those prone to the painful condition. The researchers measured nearly a dozen varieties of soybeans for oxalate, a compound that can bind with calcium in the kidney to form kidney stones.
They also tested 13 types of soy-based foods, finding enough oxalate in each to potentially cause problems for people with a history of kidney stones, according to Linda Massey, Ph.D., at Washington State University in Spokane.
The amount of oxalate in the commercial products easily eclipsed the American Dietetic Association’s 10 milligram-per-serving recommendation for patients with kidney stones, with some foods reaching up to 50 times higher than the suggested limit, she noted.
“Under these guidelines, no soybean or soy- food tested could be recommended for consumption by patients with a personal history of kidney stones,” she said.
No one had previously examined soy foods for oxalate, thus the researchers are the first to identify oxalate in store-bought products like tofu, soy cheese and soy drinks. Other foods, such as spinach and rhubarb, also contain significant oxalate levels, but are not as widely consumed for their presumed health benefits, Massey said.
During their testing, the researchers found the highest oxalate levels in textured soy protein, which contains up to 638 milligrams of oxalate per 85-gram serving. Soy cheese had the lowest oxalate content, at 16 milligrams per serving. Spinach, measured during previous research, has approximately 543 milligrams per one-cup (2 oz. fresh) serving.