What is the harm of combining oxalic acid with calcium? In fact, it is harmless to combine in a pot, in a bowl or in the mouth. Because combination is precipitation, precipitation will not be absorbed by the body, and it is only a waste of calcium at most. What is more troublesome is that oxalic acid is absorbed by human body, and then meets calcium in blood to form calcium oxalate with low solubility, especially in kidney. In the case of concentrated urine, it may cause kidney calculi, bladder stones or urethral stones.
Kidney calculi is kidney calculi, and gallstones are not diseases. According to medical statistics, about 75% of kidney calculi is precipitated by calcium oxalate, but it is also precipitated by phosphate and urate. Cholelithiasis is the precipitation of cholesterol, which has nothing to do with calcium oxalate. Some patients with gallstones are afraid to eat vegetables because they are afraid of oxalic acid, which is really a big mistake, because the prevention of gallstones needs to increase dietary fiber, and vegetables must be eaten more.
But there are still many common misunderstandings about calcium oxalate and kidney calculi. If you are impatient, please go straight to the conclusion. )
Many people think that green leafy vegetables have the highest oxalic acid content, because spinach is the representative. Some people with kidney calculi even cook every dish because they are afraid of oxalic acid. So, do all vegetables contain oxalic acid? Which is more? Let's take a look at the measurement data that can be found so far.
Oxalic acid is a common ingredient in vegetables, but its content varies greatly, up to 100 times. Generally speaking, vegetables of Chenopodiaceae, Umbelliferae and Amaranthaceae contain a little more oxalic acid. For example, the oxalic acid content of spinach is 0.97%, amaranth is 1.09%, and the coriander used to decorate plates in restaurants is as high as 1.70%. The content of oxalic acid in most wild vegetables such as Portulaca oleracea is high, reaching 1.3 1% (all the above data are measured by USDA). Therefore, many wild vegetables must be scalded with boiling water first to squeeze out bitter water before eating.
In contrast, the content of oxalic acid in vegetables belonging to Cruciferae Chinese cabbage, especially crispy vegetables, such as Chinese cabbage, Chinese cabbage, cabbage, kale, mustard greens, etc., is very, very low, below 0. 1%. The recent gas chromatographic determination in our laboratory also shows that the oxalic acid content in Chinese kale samples is lower than the detection limit. Tomatoes, cucumbers, pumpkins, potatoes and sweet peas are all low oxalic acid vegetables.
There are many vegetables, such as radish, carrot, sweet potato, watercress, eggplant, celery stalk, leek, garlic, broccoli and so on. The content of oxalic acid is between 0.2% and 0.5%.
I usually want to identify which vegetables contain more oxalic acid. In fact, the method is very simple, as long as I carefully taste whether it has astringency. The content of oxalic acid in fresh bamboo shoots, bitter gourd, water bamboo and sweet apricot (called wild vegetables in some shops) is high, which is an important reason for their astringency. Fresh bamboo shoots, in particular, are almost unpalatable if they are simply fried. It's better to boil it before cooking, it will taste much better.
At the same time, the content of oxalic acid is also greatly influenced by the differences of varieties and cultivation conditions, because oxalic acid is a defensive substance in vegetables and is related to their "resistance". Generally speaking, when there is more water, more fertilizer, better climate and fewer pests and diseases, there will be less oxalic acid in vegetables.
In addition to vegetables, many plant foods contain oxalic acid. For example, apples, apricots, plums, mangoes, cherries, pineapples and oranges all contain a small amount of oxalic acid. Blueberries, blackberries and kiwis contain more vitamins. If the fruit feels a little astringent, besides polyphenols, oxalic acid is probably also a reason.
In addition, all kinds of beans, oilseeds and nuts also contain oxalic acid, such as peanuts, melon seeds, almonds, almonds, walnuts and hazelnuts. The germ of various grains also contains oxalic acid, such as wheat germ contains a lot of oxalic acid. Soybeans and cocoa beans are even foods with high oxalic acid content, and some spices such as cinnamon are also rich. Therefore, if you drink a lot of soy milk or coffee, it is a source of oxalic acid that cannot be ignored. Oxalic acid is also found in green tea and flower and fruit tea, but I haven't seen the specific data yet.
What is eaten from food is called exogenous oxalic acid; What the body produces by itself is called endogenous oxalic acid. In fact, oxalic acid is a normal metabolite of human body, but its 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 human body cannot metabolize oxalic acid precursors into other substances, such as helping glyoxylic acid to metabolize into glycine and preventing it from forming oxalic acid, so the risk of increasing oxalic acid content in urine will be greater.
Therefore, for beauty beauty to eat too much collagen or take thousands of milligrams of vitamin C, we should be careful to increase the production of endogenous oxalic acid. A few people are keen on taking thousands of milligrams of VC every day, and no research can confirm the benefits of doing so. Increasing the risk of kidney calculi is a reliable concern (Massey L K, Liebman M, Kynast-Gales S A. Ascorbate increases the risk of human oxaluria and kidney calculi. Journal of Nutrition, 2005,135 (7):1673-1677. )。 Of course, if you only take two or three hundred milligrams of VC (2-3 small white tablets), there is no need to worry.
Because kidney calculi is mainly composed of calcium oxalate stones, the formation reason is that oxalic acid and calcium meet and combine in the kidney, so the measures to prevent kidney calculi are two aspects: reducing calcium excretion with urine or reducing oxalic acid excretion with urine.
Let's talk about ways to reduce oxalic acid first. Whether there is too much oxalic acid in the diet or too many substances metabolized into oxalic acid in the body, it may lead to an increase in the content of oxalic acid in urine. Theoretically, as long as the content of oxalic acid in urine increases, the combination of calcium and oxalic acid will increase, which may lead to an increase in the risk of calcium oxalate stones. At the same time, too high concentration of oxalic acid itself is harmful to kidney cells. Therefore, many people are very afraid of spinach and always think that there is oxalic acid in the dish, which is a health hazard.
However, a problem is neglected here: oxalic acid in spinach may not necessarily run into urine. It may be removed in cooking, or it may be combined with other substances in the gastrointestinal tract, and finally it is not absorbed into the blood, so naturally it does not necessarily bring stones. At the same time, the absorption capacity of oxalic acid in gastrointestinal tract of different people is very different. People with gastrointestinal dysfunction and "intestinal leakage syndrome" may have 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 spinach or vegetables are more likely to suffer from kidney calculi. How much food rich in oxalic acid can play a role in the formation of stones depends on what cooking method is used to cook vegetables, whether the individual's gastrointestinal tract is healthy, how the body metabolizes oxalic acid, and how many elements such as calcium and magnesium are ingested.
On the contrary, because vegetables are rich in potassium and leafy vegetables also contain more magnesium, these two elements are beneficial to reduce urinary calcium excretion, and the reduction of urinary calcium concentration is very beneficial to prevent kidney calculi. On the contrary, eating a lot of fish and seafood, taking too much protein, taking too much sodium and salt, or drinking too much sweet drinks will increase the excretion of urinary calcium and increase the risk of kidney calculi. People who use a high-protein and high-carbohydrate diet should pay special attention to the danger of kidney calculi, because this diet will lead to an increase in urine acidity, a substantial increase in calcium excretion, and a negative balance of bone calcium (Fieddy S T, Wang C Y, Khashayarsakhaee M D, et al. Effects of a low-carbohydrate and high-protein diet on acid-base balance, stone-forming tendency and calcium metabolism). American Journal of Kidney Diseases, 2002, 40(2): 265-274. )
Studies have found that excessive calcium supplementation may increase the risk of kidney calculi; But eating natural foods rich in calcium will only reduce the risk of kidney calculi. Researchers speculate that calcium in food can combine with oxalic acid in gastrointestinal tract to form calcium oxalate precipitate, which can prevent oxalic acid from being absorbed by small intestine and excreted through large intestine, which is the key to prevent kidney calculi's disease. Even if you lose some calcium, you can make up for it as long as you pay attention to eating more calcium-rich foods every day. ?
In a study in 2009, researchers asked kidney calculi patients with high oxalic acid concentration in urine to eat a high calcium diet to reduce the oxalic acid content in urine. Researchers advise patients to drink milk (300 mg of calcium, equivalent to about 250 grams of low-fat milk) and yogurt (200-400 mg of calcium, equivalent to about 200-400 grams of yogurt) every day. In addition, drink calcium-fortified soybean milk, rice slurry (soybean milk and rice slurry originally contain little calcium and cannot replace milk), or calcium-fortified fruit and vegetable juice, about 300ml. Nutritionists tailor-made calcium supplement recipes for everyone to ensure that at least 300 mg of calcium is consumed per meal. Results After eating more foods rich in calcium, their oxalic acid concentration really decreased, and at the same time, their urinary calcium excretion did not change.
This shows that oxalic acid and calcium combine in the gastrointestinal tract during cooking, and the combined calcium oxalate is discharged from the large intestine through the intestine, which actually reduces the absorption of oxalic acid in the diet. Because calcium is an extra supply, it will not reduce calcium intake or promote calcium excretion (Penniston and Nakada, 2009). Researchers are convinced that eating more calcium and combining oxalic acid in the intestine are effective measures to control hyperoxaluria.
In short, at present, the medical community believes that excessive intake of oxalic acid is not the main reason for promoting the formation of kidney calculi, but excessive intake of substances that can be metabolized into oxalic acid, too little intake of dietary calcium, or too much intake of protein are all possible reasons for promoting the formation of kidney calculi. Some people think that it may be caused by the lack of oxalic acid-degrading microorganisms in the gastrointestinal tract or the abnormal function of the gastrointestinal tract, but these claims are still in the speculative stage.
Some researchers studied the oxalic acid intake of nearly 240,000 subjects and the occurrence of kidney calculi in three large-scale epidemiological studies. The results showed that during the 44-year follow-up, there were 4605 cases of kidney calculi. Among them, the average daily intake of oxalic acid is 2 14mg for men and 185mg for women, and more than 40% of oxalic acid comes from spinach (Westerners rarely blanch spinach, and most of the time it is cooked directly or even eaten raw in salads). There was no significant difference in oxalic acid intake between kidney calculi patients and patients without kidney calculi.
Data analysis shows that the risk of kidney calculi in men who eat the most oxalic acid is 22% higher than that in men who eat the least oxalic acid, and that in elderly women is 265,438+0% higher. Compared with people who don't eat spinach at all, the kidney calculi risk of men and elderly women increased by 30% and 34% respectively, but young women were completely unaffected by spinach and oxalic acid. Researchers do not believe that oxalic acid in the diet is the main risk factor for kidney calculi. Oxalate intake and kidney calculi risk. Journal of American Society of Nephrology, 2007, 18(7): 2 198-2204. )
Even research shows that compared with the traditional American diet, the risk in kidney calculi has not increased, but decreased by more than 40% (Taylor E N, Fung T T, Curhan G C. DASH diet is related to reducing the risk in kidney calculi. Journal of American Society of Nephrology, 2009,20 (10): 2253-2259. )。 Researchers believe that eating a lot of white staple food, eating a lot of meat, drinking a lot of drinks and eating less natural miscellaneous grains and fruits are not only the root causes of chronic diseases such as diabetes and heart disease, but also reduce the metabolic function of the kidney, which may be related to kidney calculi. The study also found that obese people and patients with metabolic syndrome have an increased risk of kidney calculi.
Therefore, eating less vegetables is not an effective measure to prevent kidney calculi. If you don't eat miscellaneous grains, beans and nuts, but only eat meaty white rice and flour and drink a lot of sweet drinks every day, the intake of oxalic acid is very low, but the risk of kidney calculi will rise.
Of course, while eating foods rich in calcium as much as possible, properly controlling protein and sodium, and increasing vitamin B6 to deal with oxalic acid, we might as well reduce oxalic acid through reasonable cooking. Vegetables with high oxalic acid content, such as spinach and amaranth, can remove 40-70% oxalic acid only by boiling water. Although you will lose a little vitamin C and folic acid, you can make up for it by eating more vegetables. As for eating green leafy vegetables with low oxalic acid such as small rapeseed and Chinese cabbage, there is no need to worry. Cooking with tofu is also beneficial and harmless.
In short, there is no need to alienate spinach and amaranth because of oxalic acid. Eating more green leafy vegetables is the last word of health and an essential dietary measure to prevent osteoporosis, heart disease, diabetes, gout and Alzheimer's disease!