Medical practice has proved that caffeine in black tea can promote fat metabolism during exercise. Black tea is mild in nature and mellow in taste. Drinking black tea with sugar or milk often can not only warm the stomach, but also diminish inflammation and protect the gastric mucosa, and also has a certain effect on treating ulcers. Side effects of black tea: black tea is warm and not suitable for people who get angry. Drinking black tea for a long time will make you feel cold, your stomach is no longer as strong as before, and sometimes your kidneys will be cold and painful. In addition, it will cause palpitations and slow down the absorption rate of calcium by the body.