Spinach contains a lot of potassium oxalate, into the human body after electrolytic oxalate ions will precipitate calcium ions, not only prevent the absorption of calcium, but also easy to generate calcium oxalate stones. Experts suggest that spinach should not be eaten within 2 hours before and after taking calcium tablets, or the spinach should be boiled before potassium oxalate is dissolved in water, and the water should be poured away before eating.