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From a biological perspective overeating may be viewed as resulting from a dysregulation of appetite
The regulation of appetite (the appestat) has been the subject of much research in the last decade. Breakthroughs included the discovery, in 1994, of leptin, a hormone that appeared to provide negative feedback. Later studies showed that appetite regulation is an immensely complex process involving the gastrointestinal tract, many hormones, and both the central and autonomic nervous systems.
The hypothalamus, a part of the brain, is the main regulatory organ for human appetite. The neurons that regulate appetite appear to be mainly serotonergic, although neuropeptide Y (NPY) and Agouti-related peptide (AGRP) also play a vital role. Hypothalamocortical and hypothalamolimbic projections contribute to the awareness of hunger, and the somatic processes controlled by the hypothalamus include vagal tone (the activity of the parasympathetic autonomic nervous system), stimulation of the thyroid (thyroxine regulates the metabolic rate), the hypothalamic-pituitary-adrenal axis and a large number of other mechanisms. Opioid receptor-related processes in the nucleus accumbens and ventral pallidum effect the palatability of foods.
The hypothalamus senses external stimuli mainly through a number of hormones such as leptin, ghrelin, PYY 3-36, orexin and cholecystokinin; all modify the hypothalamic response. They are produced by the digestive tract and by adipose tissue (leptin). Systemic mediators, such as tumor necrosis factor-alpha (TNFα), interleukins 1 and 6 and corticotropin-releasing hormone (CRH) influence appetite negatively; this mechanism explains why ill people often eat less.
In addition, the biological clock (which is regulated by the hypothalamus) modifies hunger. Processes from other cerebral loci, such as from the limbic system and the cerebral cortex, project on the hypothalamus and modify appetite. This explains why in clinical depression and stress, energy intake can change quite drastically.
- ↑ Wassum KM, Ostlund SB, Maidment NT, Balleine BW. (2009). Distinct opioid circuits determine the palatability and the desirability of rewarding events. Proc Natl Acad Sci U S A. 106:12512–12517 PMID 19597155 DOI:10.1073/pnas.0905874106
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