So, how harmful is it? There are two popular sayings: (1) wasting calcium in tofu; (2) The combination of oxalic acid and calcium will lead to kidney calculi.
There is no doubt that the combined precipitation of oxalic acid and calcium does waste some calcium. Indeed, some elderly friends reported that after eating spinach and tofu, they went to the hospital for testing and found that oxalate crystals in urine increased.
However, another aspect of the problem is: if you don't eat it with tofu, won't the oxalic acid in spinach be absorbed? Will absorption not affect the utilization of calcium and promote the formation of stones? If you are worried about oxalic acid, can't you eat spinach? Then, there are many other vegetables rich in oxalic acid in the diet, such as bamboo shoots, water spinach, fungus, amaranth, cowhide, water bamboo, green garlic and so on. This may also bring the problem of increasing oxalate. Can't they eat either?
Moreover, since oxalic acid in these foods can combine with calcium, can't it be eaten with soy products? Other foods rich in calcium, such as sesame sauce, milk, shrimp skin, seafood, nuts, etc., can't you eat with them?
Analysis of these problems can be considered from four aspects.
First, can oxalic acid be removed? Without oxalic acid, all problems would be solved. Whether spinach and tofu will cause trouble depends first on how this dish is cooked. If spinach is fried directly with tofu without boiling water, it can really increase the absorption of oxalic acid. The experiment showed that the urine oxalate of blanched spinach increased less than that of directly fried spinach. When blanching, use more water and drain enough water to fully remove oxalic acid. Stir-fry the tofu first, then add the blanched spinach, turn it over a few times, the trouble caused by oxalic acid can be greatly reduced, and the delicious spinach tofu can be maintained.
Secondly, it depends on the total amount of oxalic acid consumed in one day. If spinach is cooked, but all vegetables containing a lot of oxalic acid are eaten except spinach, together, it may still bring the problem of oxalate exceeding the standard and increase the oxalate content in urine.
Third, look at the state of human digestion and absorption function and acid-base balance. Intestinal dysfunction will increase the absorption of oxalate intake, and physical acidity will also promote the formation of oxalate crystals. Studies have proved that vegetarians without animal protein have high oxalate content, but the risk of stones is very low; Eating too much meat, polished rice flour and sugary foods will promote the body to be acidic, thus increasing the risk of stones.
Fourthly, whether eating vegetables rich in oxalic acid together with tofu will increase the risk of stones. Medical investigation in China has proved that calcium supplementation is beneficial to prevent the formation of kidney and urethral stones. In other words, after eating spinach, if you don't eat bean products rich in calcium, the risk of stones is even greater. American experts even suggested that high-calcium food and oxalic acid food should be eaten together to promote the precipitation of oxalic acid in the intestine and avoid being absorbed by the human body in large quantities.
In fact, tofu rich in calcium and protein and blanched spinach rich in vitamin K, potassium and magnesium are a perfect match for supplementing calcium and strengthening bones!
This article is transferred from Sohu Health Blog: Original Nutrition Information