For many Chinese people who know a little bit about nutrition, oxalic acid seems to be a very scary thing. Spinach and tofu cannot be eaten together, and shallots and tofu cannot be eaten together. These so-called food conflict statements mostly come from the fear of the combination of oxalic acid and calcium.
What are the harmful effects of combining oxalic acid with calcium? There’s actually no harm in combining them in a pot, in a bowl, or in your mouth. Because the combination is precipitated, and the precipitate will not be absorbed by the body. At most, it is just a waste of calcium. But if oxalic acid is absorbed by the body and then encounters calcium in the blood, it forms calcium oxalate with very low solubility. Especially in the kidneys, when the urine is concentrated, it may cause problems such as kidney stones, bladder stones, or urethral stones. There is a big difference between kidney stones and gallstones. About 75% of kidney stones are calcium oxalate precipitates, and there are also phosphate and urate precipitates; while gallstones are the precipitates of cholesterol substances and have nothing to do with calcium oxalate. Some gallstone patients dare not eat vegetables because they are afraid of oxalic acid. This is really a big mistake, because to prevent gallstones, you need to increase dietary fiber and you must eat more vegetables.
However, there are still many common misunderstandings about calcium oxalate and kidney stones.
Myth 1: All green leafy vegetables contain large amounts of oxalic acid
Many people believe that green leafy vegetables have the highest oxalic acid content, because spinach is a representative example. So, do all vegetables contain oxalic acid? Which vegetables contain more oxalic acid?
Oxalic acid is a ubiquitous component in vegetables, but the content varies widely. Generally speaking, vegetables from the Chenopodiaceae, Apiaceae, and Amaranthaceae families contain relatively more oxalic acid. For example, the oxalic acid content of spinach is 0.97%, amaranth is 1.09%, and the parsley used to garnish plates in restaurants is as high as 1.70%. Most thermoplastic elastomer wild vegetables have high oxalic acid content, such as purslane, with a content of 1.31%. In contrast, vegetables of the cruciferous family Brassica genus, especially common vegetables with crisp and tender texture, such as Chinese cabbage, Chinese cabbage, cabbage, kale, mustard greens, etc., have very low oxalic acid content, below 0.1%. Tomatoes, cucumbers, pumpkins, potatoes, sweet peas, etc. are all low oxalate vegetables. There are also radish, carrot, sweet potato, watercress, eggplant, broccoli, etc., the oxalic acid content is between 0.2% and 0.5%.
On weekdays, if you want to identify which vegetables contain more oxalic acid, the method is actually very simple. Just taste them carefully to see if they have astringent taste. Fresh bamboo shoots, bitter melon, and wild rice contain high oxalic acid content, which is an important reason for their astringent taste.
Myth 2: Except for vegetables, there is no oxalic acid in other ingredients
In addition to vegetables, there are many plant foods that contain oxalic acid. For example, apples, apricots, plums, mangoes, cherries, pineapples, citrus and other fruits contain small amounts of oxalic acid. Blueberries, blackberries, and kiwis contain slightly more. If your fruit tastes a bit astringent, in addition to polyphenols, oxalic acid is probably to blame.
In addition, various beans, oil seeds and nuts also contain oxalic acid, such as peanuts, melon seeds, almonds, almonds, walnut kernels, hazelnuts, etc., which all contain a certain amount of oxalic acid. The germ of various grains also contains oxalic acid. For example, wheat germ contains a lot of oxalic acid. Soybeans and cocoa beans are even foods that are quite high in oxalic acid. Therefore, if you drink a lot of soy milk or a lot of coffee, they are both sources of oxalic acid that cannot be ignored. Oxalic acid is also present in green tea and flower and fruit tea, but there is no specific experimental data yet.
Myth 3: If you don’t eat foods with high oxalic acid content, too much oxalic acid will not enter the kidneys
What is eaten from food is called exogenous oxalic acid; and what is produced by the body itself is called endogenous oxalic acid. In fact, oxalic acid is a normal metabolic substance of the human body, but the content in the body is very low. Glycine, glycolic acid, hydroxyproline, vitamin C and other substances may be converted into oxalic acid after metabolism in the body. Especially when the intake of vitamin B6 is insufficient, the body cannot metabolize oxalic acid precursors into other substances – such as helping to metabolize glyoxylic acid into glycine to prevent it from forming oxalic acid, then the risk of increased oxalic acid content in the urine will be greater.
So, if you eat too much collagen for beauty and beauty, or take thousands of mg of vitamin C every day, you must be careful about increasing endogenous oxalic acid production.
Myth 4: Eating less vegetables can prevent kidney stones
There are two main measures to prevent kidney stones: reducing the calcium to be excreted in the urine, or reducing the oxalic acid to be excreted in the urine.
Let’s first talk about the way to reduce oxalic acid. Whether there is too much oxalic acid in the diet or too many substances that can be metabolized into oxalic acid in the body, the oxalic acid content in the urine may increase. Theoretically, as long as the urinary oxalic acid content increases, the opportunity for calcium and oxalic acid to combine will increase, which may increase the risk of calcium oxalate stones. At the same time, excessively high concentrations of oxalic acid itself can also damage kidney cells.
However, one issue is overlooked here: the oxalic acid in food may not necessarily go into urine. It may be removed during cooking, or it may be combined with other substances in the gastrointestinal tract, and ultimately not absorbed into the blood. Naturally, it will be different.It will definitely bring about the trouble of stones. At the same time, the absorption capacity of oxalic acid in the gastrointestinal tract of different people varies greatly. People with gastrointestinal dysfunction and people with “leaky gut syndrome” may have a higher absorption rate of oxalic acid in food than healthy people.
In fact, there is no reliable survey data to prove that people who eat more vegetables have a greater chance of developing kidney stones. Because vegetables are rich in potassium, and green leafy vegetables also contain more magnesium, both of these elements are helpful in reducing urinary calcium excretion, and the decrease in urinary calcium concentration is very beneficial to preventing kidney stones. On the contrary, eating a lot of fish, meat, seafood, excessive protein intake, excessive sodium intake, or drinking too many sweet drinks will increase the excretion of calcium in the urine and increase the risk of kidney stones.
The fifth misunderstanding: excessive calcium supplementation will increase the risk of kidney stones
Research has found that taking too many calcium supplements may increase the risk of kidney stones; however, consuming natural foods rich in calcium will only reduce the risk of kidney stones. Researchers speculate that calcium in food can combine with oxalic acid in the gastrointestinal tract to form calcium oxalate precipitation, which can prevent oxalic acid from being absorbed by the small intestine and allow it to pass through the large intestine and be excreted from the body. This is the key to preventing kidney stones. .
In a 2009 study, researchers had kidney stone patients with high urinary oxalate levels eat a high-calcium diet in an attempt to reduce the amount of urinary oxalate through diet. Researchers recommend that patients drink milk (containing 300 mg of calcium, approximately equivalent to 250 g of low-fat milk), plus yogurt (containing 200 mg of calcium, approximately equivalent to 200 g of yogurt) every day. In addition, drink calcium-fortified soy milk and rice milk, or calcium-fortified fruit and vegetable juice, about 300 ml. Nutritionists tailor calcium supplement recipes for each person to ensure that they consume at least 300 mg of calcium in each meal. The result was that calcium-rich foods indeed reduced their oxalate concentration, while urinary calcium excretion did not change.
This shows that oxalic acid and calcium are combined in the gastrointestinal tract during the cooking process, and the combined calcium oxalate is excreted from the large intestine, which actually reduces the amount of oxalic acid absorbed in the meal. Because calcium is added to the supply, it will not reduce the body’s calcium intake. Researchers are convinced that eating more calcium to bind it to oxalic acid in the intestines is an effective measure to control hyperoxaluria. In short, the medical community currently believes that excessive intake of oxalic acid is not the main cause of kidney stones, but excessive intake of substances that can be metabolized into oxalic acid, too little dietary calcium intake, or too much protein intake can cause kidney stones. Possible causes of kidney stone formation.
There are even studies showing that eating a DASH diet (used for Effective in controlling high blood pressure), the risk of kidney stones not only does not increase, but is reduced by more than 40% compared with the traditional American diet. Therefore, eating less vegetables is not an effective measure to prevent kidney stones.
Of course, while eating as many calcium-rich foods as possible, appropriately controlling protein and sodium, and increasing vitamin B6 to deal with oxalic acid, you may also wish to reduce oxalic acid through reasonable cooking. Spinach, amaranth and other vegetables with high oxalic acid content can remove 40% to 70% of the oxalic acid by simply blanch them in boiling water. In short, there is no need to stay away from spinach and amaranth because of oxalic acid. Eating more green leafy vegetables is the last word for health. It is an essential dietary measure for preventing osteoporosis, heart disease, diabetes, gout, and Alzheimer’s disease!
