Will eating spinach without blanching cause kidney failure? The truth is...

Rumor: "Eating unblanched spinach can cause kidney failure"

Recently, the news that "a 61-year-old man suffered kidney failure after eating unblanched spinach" became a hot topic, causing many people to worry. The rumor is that spinach contains oxalic acid, and the content is relatively high, so eating unblanched spinach is very harmful.

Rumor analysis: Exaggerating the risks.

For normal people, eating unblanched spinach will not directly lead to kidney failure, but there is a potential health risk. Spinach is rich in oxalic acid, which combines with calcium in the body to form calcium oxalate crystals. If you consume a large amount of unblanched spinach, coupled with insufficient water intake or insufficient intake of high-calcium foods, you may increase the risk of calcium oxalate stones, especially kidney stones. If kidney stones are not treated for a long time, they may cause kidney damage, but this process is slow and is not equivalent to "kidney failure."

The fundamental reason why the man in the news suffered from kidney failure was not a simple plate of spinach, but that he had an underlying disease. Of course, oxalic acid is not a nutrient, and it is better for normal people to eat less. It is also easily soluble in water, so it is recommended that you blanch the spinach before eating it.

A few days ago, a piece of news became a hot search, saying that "a 61-year-old man suffered kidney failure after eating unblanched spinach." In this era when many people are accustomed to "not reading too long" and only get information through headlines, information such as "unblanched spinach can cause kidney failure" will naturally become a hot topic.

Simply put, this is a typical example of traffic media using the technique of "tailoring facts" to scare the public.

Spinach is a common vegetable. Like many plant foods, it contains oxalic acid. Among various foods, spinach does have a relatively high oxalic acid content. Oxalic acid is an organic acid that is not needed by the human body and cannot be used by the human body. After it is eaten, it is absorbed into the blood in the gastrointestinal tract and then filtered and excreted by the kidneys. As long as the kidney function is normal, the oxalic acid in general food can be excreted smoothly and has no effect on the human body. However, if the kidney function is damaged, such as renal failure or nephritis, oxalic acid is difficult to be excreted smoothly and accumulates in the kidneys. Excessive oxalic acid concentration in the kidneys can cause damage to kidney tissue, further deteriorate kidney function and lead to renal failure. In addition, excessive concentrations of oxalic acid can also react with calcium to form calcium oxalate crystals, which become kidney stones. Calcium oxalate is not the only cause of kidney stones, but most kidney stones are calcium oxalate stones.

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Therefore, people with impaired kidney function, such as the man with chronic kidney disease in the news, need to avoid oxalic acid intake. The root cause of his illness after eating "unblanched spinach" was the existing chronic kidney disease, not how "toxic" the spinach was. This is like a diabetic who gets sick after drinking a bottle of beverage, because "the sugary beverage causes the diabetic's blood sugar to go out of control", not because the beverage "causes diabetes". In short, oxalic acid is not a nutrient, and the less oxalic acid in the diet, the better. For people with healthy kidney function, the oxalic acid in the regular diet can be smoothly processed without causing harm, while for people with imperfect kidney function, the difficulty of oxalic acid being smoothly excreted may further worsen the kidney condition, so it is necessary to avoid "oxalic acid diet". Oxalic acid is easily soluble in water. Vegetables with relatively high oxalic acid content, such as spinach, amaranth, leek, celery, etc., can remove a considerable part of the oxalic acid by blanching them in boiling water. For people with kidney disease, if they like these vegetables, blanching is necessary; and for people with healthy kidneys, reducing oxalic acid intake is also beneficial and harmless, and can make these vegetables more delicious.

Looking in the mirror of rumors

We are often frightened by some shocking headlines in the news, but this is often a misunderstanding caused by only revealing part of the facts. For example, "A plate of unblanched spinach caused kidney failure" is such an example. When we click on the news, we will see that the man's underlying disease is the root cause of kidney failure, not spinach. Therefore, this also reminds us that we must receive information comprehensively and carefully, rather than being deceived by "headline parties".

Author: Yun Wuxin, PhD in Food Engineering, Science Writer

Review丨Ruan Guangfeng, Deputy Director of the Kexin Food and Health Information Exchange Center