Three meals a day and eating on time are related to the biological rhythm of the human body. Three meals a day are served in the morning, noon and evening respectively. During these three times, digestive enzymes in human gastrointestinal tract are particularly active, which is ready for digesting food. Eating at this time is very beneficial to food digestion and absorption. When to eat is related to the adjustment of human biological clock. Once disturbed, the function of gastrointestinal tract will be affected first.