When you eat foods containing oxalic acid, this substance can interfere with the absorption of minerals in those foods, such as calcium, magnesium and potassium. Oxalic acid also can combine with minerals in the body, creating oxalate crystals that may cause problems for people prone to kidney stones or gout. The U.S. Department of Agriculture lists oxalic acid content in foods by parts per million (ppm), as compiled by Jim Duke, Ph.D.
Leafy Green Vegetables
Leafy green vegetables contain high amounts of oxalic acid. They include lambsquarter with 300,000 ppm, purslane at nearly 17,000 ppm, spinach at 6,580 ppm and mustard greens at about 1300 ppm. OxalicAcidInfo.com also lists beet greens, endive and Swiss chard as high in oxalic acid.
Other Vegetables
Many other vegetables contain oxalic acid. Sweet potatoes and many types of peppers contain about 1000 ppm, including bell, green and sweet peppers. Beets and pumpkin have about 400 ppm. Eggplant, tomatoes, cassava, potatoes, okra, corn, parsnips, radishes and cauliflower also contain over 60 ppm oxalic acid.
Beans
Beans are another source of oxalic acid. Soybeans have 770 ppm and lentils about 200 ppm. Other beans containing oxalic acid include kidney, navy, snap, string and wax beans, all with over 200 ppm.
Fruit
Star fruit (carambola) contains up to 95,800 ppm oxalic acid. Eating this fruit poses other health risks for patients with kidney dysfunction, as explained by a study published in a 2003 issue of the journal "Nephrology Dialysis Transplantation." Star fruit contains a neurotoxin that can lead to severe neurological problems for people whose kidneys do not provide proper filtration. The study notes that star fruit also has a high oxalic acid content that may cause severe, although reversible, toxic effects on the kidneys in these patients. Other fruits containing oxalic acid include bananas at 5,240 ppm, and mangoes, black currants, pomegranates and oranges at over 80 ppm.
Grains, Nuts and Herbs
Some grains, nuts and herbs contain oxalic acid. The highest amounts occur in buckwheat, at 111,000 ppm. Almonds and cashews contain over 3000 ppm oxalic acid. Black pepper and white pepper have 34,000 ppm, poppyseeds 16,200 and ginger 5000 ppm. Parsley, chives, oats and wheat also contain oxalic acid.
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