appetite n : a feeling of craving something; "an appetite for life"; "the object of life is to satisfy as many appetencies as possible"- Granville Hicks [syn: appetency, appetence]

English

Etymology

Old English appetit, French appétit, from Latin appetitus, from appetere to strive after, long for; ad + petere to seek. See Petition, and compare with Appetence.

Pronunciation

• WEAE ˈæp.ə.taɪt

Noun

1. Desire for, or relish of, food or drink; hunger.
2. Any strong desire; an eagerness or longing.

   If God had given to eagles an appetite to swim. --Jer. Taylor.

   To gratify the vulgar appetite for the marvelous. --Macaulay.

3. The desire for some personal gratification, either of the body or of the mind.

   The object of appetite is whatsoever sensible good may be wished for; the object of will is that good which reason does lead us to seek. --Hooker.

Derived terms

• appetitive
• appetizer
• appetizing
• appetizingly

Synonyms

• craving; longing; desire; appetency; passion

Quotations

“And I return with an excellent appetite. There can be no question, my dear Watson, of the value of exercise before breakfast. But I am prepared to bet that you will not guess the form that my exercise has taken.”

—Sir Arthur Conan Doyle in The Adventure of Black Peter

Translations

• Croatian: apetit
• Danish: appetit
• French: appétit
• German: Appetit
• Greek: όρεξη
• Japanese: 食欲 (shokuyoku)
• Slovak: chuť
• Spanish: apetito
• Portuguese: Apetite

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 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.

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