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. I have always had a whitening method. I don't know if you like it or not, but if you can stick to it. That is … keep exercising and drink pure milk every day!