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Information about Appetite

For the mineral, see .
The appetite is the desire to eat food, felt as hunger. Appetite exists in all higher lifeforms, and serves to regulate adequate energy intake to maintain metabolic needs. It is regulated by a close interplay between the digestive tract, adipose tissue and the brain. Decreased desire to eat is termed anorexia, while polyphagia (or "hyperphagia") is increased eating. Disregulation of appetite contributes to anorexia nervosa, bulimia nervosa, cachexia, overeating, and binge eating disorder.

Regulation

The regulation of appetite 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.

Effector

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.

Sensor

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.

Role in disease

A limited or excessive appetite is not necessarily pathological. Abnormal appetite could be defined as eating habits causing malnutrition on the one side or obesity and its related problems on the other.

Both genetic and environmental factors may regulate appetite, and abnormalities in either may lead to abnormal appetite. Poor appetite (anorexia) may have numerous causes, but may be a result of physical (infectious, autoimmune or malignant disease) or psychological (stress, mental disorders) factors. Likewise, hyperphagia (excessive eating) may be a result of hormonal imbalances, mental disorders (e.g. depression) and others.

Dysregulation of appetite lies at the root of anorexia nervosa, bulimia nervosa and binge eating disorder. In addition, decreased response to satiety may promote development of obesity.

Various hereditary forms of obesity have been traced to defects in hypothalamic signalling (such as the leptin receptor and the MC-4 receptor), or are still awaiting characterisation (Prader-Willi syndrome).

Pharmacology

Mechanisms controlling appetite are a potential target for weight loss drugs. Early anorectics were fenfluramine and phentermine. A more recent addition is sibutramine (Reductil®, Meridia®), which increases serotonin and noradrenaline levels in the central nervous system. In addition, recent reports on recombinant PYY 3-36 suggest that this agent may contribute to weight loss by suppressing appetite.

Given the epidemic proportions of obesity in the Western world, developments in this area are expected to snowball in the near future, as dieting alone is ineffective in most obese adults.

Further reading

  • Neary NM, Goldstone AP, Bloom SR. Appetite regulation: from the gut to the hypothalamus. Clin Endocrinol (Oxford) 2004;60:153-60. PMID 14725674.
  • Wynne K, Stanley S, Bloom S. The gut and regulation of body weight. J Clin Endocrinol Metab 2004;89:2576–82. PMID 15181026.
Desire may refer to:

Feelings

  • Interpersonal attraction
  • Preference, on which microeconomic theory is based
  • Motivation, thought that leads to an action
  • Tanha in Buddhist psychology, as described in the Four Noble Truths

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eating (formally, ingestion) is the process of consuming nutrition, i.e. food, for the purpose of providing for the nutritional needs of an animal, particularly their energy requirements and to grow.
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Food is any substance, usually composed primarily of carbohydrates, fats, water and/or proteins, that can be eaten or drunk by an animal or human being for nutrition or pleasure.
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Hunger is a feeling experienced when the glycogen level of the liver falls below a threshold, usually followed by a desire to eat. The usually unpleasant feeling originates in the hypothalamus and is released through receptors in the liver.
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Metabolism is the complete set of chemical reactions that occur in living cells. These processes are the basis of life, allowing cells to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories.
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gastrointestinal tract (GI tract), also called the digestive tract, or the alimentary canal, is the system of organs within multicellular animals that takes in food, digests it to extract energy and nutrients, and expels the remaining waste.
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adipose tissue or fat is loose connective tissue composed of adipocytes. Its main role is to store energy in the form of fat, although it also cushions and insulates the body.
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In animals, the brain or encephalon (Greek for "in the skull"), is the control center of the central nervous system, responsible for behavior. The brain is located in the head, protected by the skull and close to the primary sensory apparatus of vision, hearing,
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Anorexia
Classifications and external resources

ICD-10 R 63.0
ICD-9 783.0

Anorexia (deriving from the Greek "α(ν)-" (a(n)-, a prefix that denotes absence) + "όρεξη'' (orexe)
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Polyphagia
Classifications and external resources

ICD-10 R 63.2
ICD-9 783.6

In biology, "polyphagia" is a type of phagy, referring to an animal that feeds on many kinds of food.

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Anorexia Nervosa
Classification & external resources

ICD-10 F 50.0 -F 50.1
ICD-9 307.1

OMIM 606788
DiseasesDB 749

eMedicine emerg/34   med/144

For the symphonic black metal band, see Anorexia Nervosa (band)''

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Bulimia nervosa
Classification & external resources

ICD-10 F50.2
ICD-9 307.51

Bulimia nervosa, commonly known as bulimia , is an eating disorder and psychological condition in which the subject engages in recurrent binge eating followed by
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Cachexia
Classifications and external resources

ICD-10 R64
ICD-9 799.4

Cachexia (pronounced IPA: /kəˈkɛksiə/
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Overeating is a behavior that, while generally not a medical problem, in some cases is a symptom of binge eating disorder or bulimia. In more general terms it refers to the persistent consumption of excess food in relation to the energy that the person expends, leading to weight
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citation, footnoting or external linking.
Binge eating disorder (BED), is a psychiatric disorder in which a subject shows the following symptoms.
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20th century - 21st century - 22nd century
1970s  1980s  1990s  - 2000s -  2010s  2020s  2030s
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Identifiers
Symbol LEPR

Entrez 3953
HUGO 6554
OMIM 601007

RefSeq NM_002303
UniProt P48357
Other data

Locus Chr. 1 p31 Leptin
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gastrointestinal tract (GI tract), also called the digestive tract, or the alimentary canal, is the system of organs within multicellular animals that takes in food, digests it to extract energy and nutrients, and expels the remaining waste.
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hormone (from Greek όρμή - "to set in motion") is a chemical messenger that carries a signal from one cell (or group of cells) to another. All multicellular organisms produce hormones (including plants - see phytohormone).
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The central nervous system (CNS) represents the largest part of the nervous system, including the brain and the spinal cord. Together with the peripheral nervous system, it has a fundamental role in the control of behavior.
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autonomic nervous system (ANS) (or visceral nervous system) is the part of the peripheral nervous system that acts as a control system, maintaining homeostasis in the body. These maintenance activities are primarily performed without conscious control or sensation.
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The hypothalamus links the nervous system to the endocrine system via the pituitary gland (hypophysis). The hypothalamus, (from Greek ὑποθαλαμος = under the thalamus) is located below the thalamus, just above the brain stem.
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Neurons (also known as neurones and nerve cells) are electrically excitable cells in the nervous system that process and transmit information. In vertebrate animals, neurons are the core components of the brain, spinal cord and peripheral nerves.
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Serotonin (pronounced IPA: /ˌsɛrəˈtoʊnən/) (5-hydroxytryptamine, or 5-HT) is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system (CNS) and
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Neuropeptide Y (NPY) is a 36 amino acid peptide neurotransmitter found in the brain and autonomic nervous system. It augments the vasoconstrictor effects of noradrenergic neurons.
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Agouti-related protein also called Agouti-related peptide (AgRP) is a neuropeptide produced in the brain (in the arcuate nucleus of the hypothalamus) by the AgRP/NPY neuron that increases appetite and decreases metabolism and energy expenditure.
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The vagus nerve (also called pneumogastric nerve or cranial nerve X) is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem (within the medulla oblongata) and extends, through the jugular foramen, down below the head, to the
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parasympathetic nervous system (PSNS) is one of three divisions of the autonomic nervous system (ANS). The ANS -a subdivision of the peripheral nervous system (PNS)- is subdivided into the sympathetic (SNS), parasympathetic (PSNS) and enteric (bowels) nervous system (ENS).
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autonomic nervous system (ANS) (or visceral nervous system) is the part of the peripheral nervous system that acts as a control system, maintaining homeostasis in the body. These maintenance activities are primarily performed without conscious control or sensation.
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