The history is unclear, but the collocation of this dish is not very scientific, because tofu is rich in protein, calcium and other nutrients, while 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 precipitated calcium oxalate, which destroys the calcium in tofu. Calcium oxalate is difficult to be absorbed by human body. If long-term consumption of shallots mixed with tofu will cause calcium deficiency in the human body and prone to cramps and rickets.