Most kidney stones are made up of calcium oxalate. To prevent them, it is necessary to know the list of foods richest in oxalates and reduce their consumption.
Oxalates, salts of oxalic acid, are substances present in foods of plant origin that, in high doses, can be harmful to health, since they favor the formation of kidney stones and can hinder kidney function.
It is also known that although oxalates and uric acid are different substances, by acting both on the function of the kidney they can have a synergistic effect, and the presence of one aggravate the problems derived from the other.
It is known that up to 80% of the stones are formed of calcium oxalate, but only 10-20% of the oxalate present in the urine is of dietary origin, the rest is generated by the body itself. Thus, although it is popularly said that foods with oxalates are prohibited for kidney stones, it is not really necessary to eliminate them completely from the diet. Simply do not abuse foods that contain them in remarkable quantities.
Therefore, when there is a tendency to form oxalate stones, it is important to know which foods have oxalate and how they are produced, to adopt some measures to prevent its accumulation in the body.
OXALATE KIDNEY STONES: WHY THEY OCCUR
Kidney stones are a common pathology: in most underdeveloped countries their incidence is estimated at 5% of the population; in Europe, around 10%; in the US, 12%; and in Saudi Arabia up to 20% of the population suffers from this problem.
The stones are produced by the presence of abnormal urine (modified in its composition for metabolic reasons), which causes a greater amount of uric acid, calcium and oxalates, which increases the predisposition to form saline microcrystals that, when agglutinated, generate kidney stones.
It is also known that certain substances present in the urine (citrates, nephrocalcin and glycolysis) act as inhibitors of stone formation.
Of these figures, 60%-80% of cases are calcium oxalate stones; Thus, the incidence of oxalate stones has almost doubled in the last 50 years and has gone hand in hand with the increase in spending on the shopping basket.
Interestingly, the increase by food groups has not been on par with that of dietary oxalates, since most vegetables with oxalates were considered foods of “poor people” (spinach, chard …). Therefore, it is not yet known whether there is a direct relationship between oxalic stones and oxalates ingested with diet.
Kidney stones are linked to genetic conditioning and aspects such as the accumulation of substances in the kidney, such as uric acid.
There are families of stone formers, reinforcing the idea that there is a family predisposition and a matter of transmission of habits, such as drinking more or less liquids, an important dietary factor in the formation of kidney stones.
Therefore, in addition to moderating the consumption of foods rich in oxalates, it is convenient to follow a diet low in purines, which are rich in uric acid.
FOODS WITH OXALATES THAT ARE NOT SUITABLE FOR KIDNEY STONES
This table shows the oxalate content per 100 g of feed. Data Source Provider: Justus von Liebig University of Giessen (Germany).
| Spinach | 571 mg |
| Rhubarb | 537 mg |
| Cocoa powder | 385 mg |
| Beetroot | 72.2 mg |
| Green bean | 43.7 mg |
| Brown bread | 20.9 mg |
| Raspberry | 16.4 mg |
| Strawberry | 15.8 mg |
| Tea | 12.5 mg |
| Blackberry | 12.4 mg |
| Plum | 11.9 mg |
| Milk chocolate | 11.2 mg |
| Redcurrant | 9.9 mg |
| Eggplant | 9.5 mg |
| Artichoke | 8.8 mg |
| Grape | 7.9 mg |
| Red cabbage | 7.4 mg |
| Cherry | 7.2 mg |
| White bread | 6.9 mg |
| Apricot | 6.8 mg |
| Celery | 6.8 mg |
| Cauliflower | 6.6 mg |
| Orange | 6.2 mg |
| Pear | 6.2 mg |
| Brussels sprouts | 6.1 mg |
| Carrot | 6.1 mg |
| Parsley | 5.7 mg |
| Jam | 5.7 mg |
| Kale | 4.9 mg |
| Wine | 3.1 mg |
DIET TO AVOID OXALATE STONES
If the above is taken into account, it can be recommended that if you have ever suffered from kidney stones due to accumulation of oxalates, the most appropriate diet should be based mainly on the consumption of plant foods. In addition, other considerations must be taken into account:
- The consumption of proteins of animal origin, however, does favor the appearance of stones, so its consumption should be moderated. It is advisable to reduce meat foods as much as possible (red meat, sausages …).
- Cooking can reduce oxalates by 10-15%, but also reduces vitamin content.
- When there is a predisposition to suffer from oxalic stones, it is recommended not to abuse foods rich in oxalic acid salts. However, this relationship is not widely proven. In addition, oxalic acid salts are hardly soluble in water, so they remain in the feed and can form stones. If these salts had a high solubility in water, they would simply be eliminated in the urine.
- Vitamin C is ascorbic acid, and ascorbates, metabolically, can be transformed into oxalates. This pathway is only important when consuming large amounts of vitamin C, as happens when following a supplementation of 500 mg to 1 g daily, for example, to treat a cold.
- It is advisable to drink 2.5 to 3 liters of fine water daily (between 400 mg and 1 g of dry residue), preferably at night to prevent salts from accumulating in the kidneys. Drinking plenty of fluids helps expel oxalate stones, although oxalic acid stones are sharp and thorny, so their expulsion is quite painful.
- Does too much calcium cause kidney stones? The excessive expulsion of calcium may be due to an increase in the consumption of proteins, which need this mineral for metabolic absorption, which can generate kidney stones, cramps due to a calcium deficit or osteoporosis. But this can happen whether there is an excess of calcium in the body or not.