There is a two-part allegorical saying called "spring onion mixed with tofu-clear and white". Onion mixed with tofu is an ordinary home-cooked dish, and many people like it. But this way of eating is not scientific. Because tofu is rich in nutrients such as protein and calcium. Onion contains a lot of oxalic acid. When tofu is mixed with onion, the calcium in tofu combines with oxalic acid in onion to form white precipitate calcium oxalate, which destroys the calcium in tofu. Calcium oxalate is an object that is difficult for human body to absorb. If long-term consumption of shallots mixed with tofu will cause calcium deficiency in human body, which will lead to cramps and chondrosis.

According to nutritionists' research, tofu contains calcium and shallots contain oxalic acid, and the two are fused to form a white precipitate-calcium oxalate, which is not easily absorbed by the human body. This not only destroys the nutritional value of tofu, but also may form stones in the body, endangering human health.