[Chronobiology, nutrition and metabolism].

The "nutrition" function is fulfilled by a succession of physiologic actions of which the first is eating and the last is the intracellular metabolism of nutrients. These actions involve not only sensory processes subjected to neurocentral regulation but also peripheral metabolic, and hormonal processes. The physiologic "nutrition" function involves a number of parameters for which fundamental rhythms have been demonstrated, such as eating behaviors, intra- and extracellular metabolisms, hormone secretions and their effects on target organs, and use of food and nutrients. Each of these rhythms can be demonstrated under physiologic conditions but can be modified by environmental factors (temperature, light, seasons, physical and mental activity), disease states (many diseases can produce profound alterations in nutritional regulation processes), and drugs. Interactions between these rhythms also exist; for instance, eating behavior rhythms can be modified by sociocultural pressures and this can, in turn, modify the fundamental rhythms of biologic parameters. The unit of time that allows the study of these rhythms varies: in addition to circadian and ultradian rhythms, weekly (cisaseptian) and annual (circannual) cyclical changes should be taken into account when investigating human nutrition.