Coffee contains caffeine, which will stimulate sympathetic nerves after entering the body, thus eliminating drowsiness, improving blood circulation and making the body feel warmer without fatigue, so it has a "refreshing" effect. But the stimulation and excitement of sympathetic nerve has a negative effect on appetite, that is, appetite will decrease, so drinking coffee before meals will make you unwilling to eat. In addition, because the stomach is stimulated, the secretion of gastric juice increases, which stimulates fasting, which is not good for patients with gastric ulcer. This can be said to be the negative effect of coffee. But drinking after meals will help digestion, because the secretion of gastric juice will increase. So it's absolutely no problem to drink after meals. In addition, some people think that adding some milk can alleviate its stimulating effect, but how much caffeine can a small amount of milk neutralize? Unless it is half milk and half coffee, making coffee milk or milk coffee may be effective. For example, drinking coffee and milk for breakfast, because milk is more than coffee, although it is drunk on an empty stomach, it still has the effect of relieving gastric juice. The ideal thing is to drink it after meals, which is beneficial and harmless. If you drink coffee in the morning, you should drink it half an hour after breakfast. Of course, the so-called "too much is too late", even the best things should be "enough is enough". Otherwise, whether drinking before or after meals, excessive caffeine will cause palpitations (heart beating badly), and even side effects such as trance and unstable walking center of gravity. In principle, two or three cups of coffee a day are appropriate. Most people will feel sick if they drink four or five cups, so be careful. In principle, no matter what kind of stimulating drinks, it is better not to exceed three cups a day.