Chronobiology deals with temporal changes in body functions. There is clear evidence for a ”body clock” which affects many aspects of physiology and biochemistry. Food intake is determined mainly by our habits ad lifestyle, and this is reflected in gut function and influenced also by the body clock, particularly when the hormonal control of metabolism slowly, the rhythms of food intake and metabolism will not adjust fully and immediately to time-zone transition and night work. Current knowledge provides a rationale for reducing these difficulties.