Body weight of man and animals is under homeostatic control mediated by the adjustment of food intake. It is discussed in this review that besides signals reporting energy deficits, optimized programs of body clocks take part in feeding behaviour as well. Circadian light- and food-entrainable clocks determine anticipatory adaptive behavioural and physiological mechanisms, promoting or inhibiting food intake. In fact these clocks form the constraints within which the homeostatic regulation of feeding behaviour is operating. Therefore, a strong interaction between circadian and homeostatic regulation must occur. In this homeostatic control, a wide variety of regulatory negative feedback mechanisms, or satiety signals, play a dominant role. In this respect several gut hormones and body temperature function as 'short-term' satiety factors and determine meal sizes and intermeal intervals. Leptin, secreted by fat cells in proportion to the size of adipose tissue mass, is probably an important determinant of the 'long-term' regulation of feeding behaviour by setting the motivational background level for feeding behaviour. Thus, initiation or termination of meals at any particular point in time, depends on the resultant of all satiety signals and on constraints imposed by circadian light- and food-entrainable oscillators.