Research on the regulation of food intake has been carried out for many years, but the mechanism of the human regulation of food intake has not been elucidated yet. Three main levels of food intake regulation may be distinguished. These include the level of the gastrointestinal tract and the level of the hypothalamus in the brain. These first two levels will provide input to the cortex resulting in behavior after further integration with cognitive processes (third level).
The gastrointestinal tract and nervous system, both central and enteric, are involved in two-way extrinsic communication by parasympathetic and sympathetic nerves, each comprising efferent fibers and afferent sensory fibers required for gut-brain signaling. Afferent nerves are equipped with numerous sensors at their terminals in the gut related to visceral mechano-, chemo- and noci-receptors, whose excitations may trigger a variety of visceral reflexes regulating gastrointestinal functions and appetitive behavior. Food intake depends upon various influences from the central nervous system as well as from the body energy stores.
The complexity and the central level of integration of food intake regulatory signals are the reason for the lack of full understanding of food intake regulation in humans. Animal research has unraveled part of this central regulation which takes place mainly in the hypothalamus. However, the regulation of food intake in humans may be different from animals but investigating these central mechanisms is extremely difficult in humans. Apart from the complexity and limited technological possibilities, new hormonal factors involved in food intake regulation are still being identified (e.g. ghrelin and obestatin). Lastly, humans do not eat solely in response to a metabolic need for nutrients, but also in response to non-physiological factors that are hard to control in a research setting.
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