Oxalates, calcium oxalate, oxalate stones

The Enemy of Football

Oxalic acid is an anti-nutritional factor present in many foods, including spinach, rhubarb, whole grains and cabbage. Once ingested it combines with different minerals (iron, magnesium and above all calcium) forming salts, called oxalates, which prevent it from being absorbed. Because of their ability to reduce the minerals available to the body, oxalates promote the onset of deficiency states (osteoporosis, anemia etc.).

The consumption of oxalic acid becomes even toxic when it reaches doses equal to or greater than 1500 mg. In such situations the ingested oxalates are rapidly absorbed in the small intestine and go to bind with serum calcium. The consequent decrease in the concentration of the mineral in the blood causes severe disorders, such as involuntary muscle contractions, tremors, cramps and tetanic crises.

Foods rich in oxalates can be harmful even if ingested in non-lethal doses. Combined with calcium, oxalic acid gives rise to calcium oxalate, an insoluble salt that tends to precipitate in the form of crystals and to accumulate in the urinary tract (kidney stones). When these hard and crystalline formations reach significant dimensions, disorders such as irritation of the urinary tract, haematuria (presence of blood in the urine) and kidney damage arise. For this reason, in the presence of oxalate stones, the diet should not provide more than 100 mg of oxalic acid a day. To learn more about the topic: diet and kidney stones.

Food Oxalic Acid Content
Type of food	mg / 100g	Type of food	mg / 100g
Beets	690	strawberries	15
spinach	676	Raspberries	15
Cocoa powder	450	blueberries	15
Red beet (roots)	338	apricots	14
Bitter chocolate	80	Eggplant	12
Cauliflower	60	You	10
Celery (coasts)	50	tomatoes	7.5
Milk chocolate	35	Green cabbage (cabbage)	7.3
Celery of Verona	34	Bananas	6.4
carrots	33	Pineapple in syrup	6.3
Green beans	30	Brussels sprouts	5.9
Curly chicory	27	Potatoes	5.7
Envy	27	Oats (flakes)	5.6
escarole	27	Asparagus	5.2
Cucumbers	25	beans	4.3
oranges	24	Currant	4
onions	23	Fresh peas	1.3
Blackberries	18	Peaches in syrup	1.2
peppers	16	Coffee	1

In addition to the presence of oxalic acid in a given food, it is also necessary to evaluate the bioavailability of the calcium contained in it. This parameter is obtained from the ratio between the quantities of oxalic acid and those of calcium (g / kg). Foods in which this ratio exceeds 2.25 may be considered "descaling agents", as well as a bad source of calcium. This ratio is less than one in lettuce, cabbage, pea and onion; it is around the unity in the potato and in the currant, while it reaches values ​​of 7 in the beet, in the spinach and in the cocoa.