Oxalic acid, or dicarboxylic acid, is a naturally occurring substance found in plants, animals and in humans. In chemical terms, oxalates belong to a group of molecules called organic acids and the body’s cells routinely convert other substances into oxalates such as vitamin C.
Oxalic acid is a chemical compound of hydrogen, carbon and oxygen. It is a colourless, crystalline substance that is poisonous to humans in its pure form or when it is dissolved in a liquid to make a concentrated solution. Toxic levels of oxalic acid are found in products such as certain wood cleaners, metal cleaners, rust treatments, bleaches, disinfectants and pesticides.
Oxalic acid is found in many plants, but at much lower concentrations than in synthetic products. Most of these plants are completely safe for human consumption, but some contain enough oxalic acid to cause health problems in certain people such as the formation of calcium oxalate kidney stones.
Without oxalic acid, foods such as spinach and kale would have a much higher, bio-available calcium content than they do because it is bound up with oxalic acid and, in most people, it is passes out through the urine.
Oxalic acid often exists in the form of oxalates in plants. When an oxalic acid molecule loses its two hydrogen atoms it forms an oxalate ion. Oxalate ions join with certain metal ions to form oxalate salts, such as calcium oxalate and magnesium oxalate.
Calcium oxalate kidney stones
Calcium oxalate has very low solubility in water and tends to form crystals instead of dissolving and this is why, in some people, these crystals form large stones in the kidneys that cause excruciating pain and require medical attention.
People at risk for forming calcium oxalate kidney stones are generally advised to follow a low oxalate diet. However, the formation of kidney stones containing oxalate is an area of controversy in clinical nutrition with respect to dietary restriction of oxalate.
Recent research studies have shown that intake of protein, calcium and water influences calcium oxalate stone formation as much as, or more than, the intake of oxalate. Some foods, that have traditionally been assumed to increase stone formation because of their oxalate content (like black tea) actually appear, in more recent research, to have a preventive effect.
When the oxalic acid has become inorganic by cooking or processing the foods that contain it, then this acid forms an interlocking compound with the calcium even combining with the calcium in other foods eaten during the same meal, destroying the nourishing value of both.
Therefore, in its raw form, oxalic acid is beneficial and not going to cause kidney stones and when oxalic acid is in the blood it kills bacteria and viruses and decalcifies the material in plaque in arteries and is present in the blood of all warm-blooded mammals.
Oxalic acid encourages the cellular production of energy and is a natural preservative. There has also been some evidence to suggest that having adequate levels of oxalic acid in the blood eliminates abnormal cells in the body effectively with no harmful side effects which may reduce the risks of tumours and cancer.
Foods rich in oxalic acid in alphabetical order
- Almonds
- Aubergine
- Beans (green, runner)
- Beetroot
- Bell peppers (green)
- Berries
- Blackcurrants
- Bran
- Cabbage
- Carrots
- Cashews
- Celery
- Citrus peel
- Chives
- Chocolate
- Cinnamon
- Cocoa
- Coffee
- Collard greens
- Corn silk
- Dandelion
- Figs
- Fizzy drinks
- Grapes (purple)
- Gooseberries
- Kale
- Kiwifruit
- Leeks
- Legumes
- Mustard (greens)
- Nuts
- Okra
- Parsley
- Parsnips
- Peanuts
- Pecans
- Pepper
- Plums
- Potatoes
- Prunes
- Quinoa
- Red currants
- Rhubarb
- Sesame butter (tahini)
- Sorrel
- Soya beans
- Spinach
- Squash
- Strawberries
- Swede
- Sweet potatoes
- Swiss chard
- Tangerines
- Tea (black)
- Tomatoes
- Walnuts
- Watercress
- Wheat
- Yams
Related subjects
- A-Z of nutrients
- Calcium
- Magnesium
- Urinary system disorders (kidney stones)
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