The traditional saying that "onion mixed with tofu, one is clear and two are white" has been completely subverted in these "food-like" theories, and home-made preserved eggs and onion mixed with tofu are listed as one of the top diet killers. According to the book, tofu contains a lot of calcium and shallots contain a certain amount of oxalic acid. If eaten, it will combine into calcium oxalate, which is not easily absorbed by the human body and will lead to stones.

But I have eaten it for so many years, and there is nothing wrong with it.