Black coffee contains caffeine and other substances, and moderate drinking can improve metabolism to some extent. Because the high content of caffeine in black coffee can stimulate sympathetic nerve, make the gastrointestinal tract secrete more digestive juice to promote digestion, prevent bloating, and also promote gastrointestinal peristalsis, which has a laxative effect. In addition, caffeine in black coffee has the function of invigorating the spirit and diuresis, which is beneficial to fat decomposition, reducing fat accumulation and reducing weight.