Our conventional wisdom is that spinach contains high levels of oxalic acid and tofu contains calcium, and that oxalic acid and calcium combine to produce water-insoluble calcium oxalate, which creates stones. In fact, the probability of stones forming when spinach and tofu are eaten together is very low. Because oxalic acid and calcium combined to produce calcium oxalate is required to reach a certain amount, and spinach in the production process after blanching, frying oxalic acid has been lost a lot, at the same time, oxalic acid is soluble in water, so spinach a tofu with eating the probability of forming stones is very small.