Fish, shrimp and algae in seafood are rich in nutrients such as protein and calcium. If eaten with fruits containing tannic acid, it will not only reduce the nutritional value of protein, but also easily combine calcium in seafood with tannic acid into new indigestible substances, which will stimulate the stomach and cause discomfort, stomach pain, vomiting, nausea and other symptoms. Fruits with more tannic acid include persimmon, grape, pomegranate, hawthorn and olive.