Anorexia (from Ancient Greek ανορεξία: ‘ἀν-‘ “without” + ‘όρεξις’, spelled ‘órexis’ meaning “appetite”) is the decreased sensation of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a decreased appetite, some of which may be harmless, while others indicate a serious clinical condition or pose a significant risk.
For example, anorexia of infection is part of the acute phase response (APR) to infection. The APR can be triggered by lipopolysaccharides and peptidoglycans from bacterial cell walls, bacterial DNA, and double-stranded viral RNA, and viral glycoproteins, which can trigger production of a variety of proinflammatory cytokines. These can have an indirect effect on appetite by a number of means, including peripheral afferents from their sites of production in the body, by enhancing production of leptin from fat stores. Inflammatory cytokines can also signal to the central nervous system more directly by specialized transport mechanisms through the blood–brain barrier, via circumventricular organs (which are outside the barrier), or by triggering production of eicosanoids in the endothelial cells of the brain vasculature. Ultimately the control of appetite by this mechanism is thought to be mediated by the same factors normally controlling appetite, such as neurotransmitters (serotonin, dopamine, histamine, norepinephrine, corticotropin releasing factor, neuropeptide Y, and α-melanocyte-stimulating hormone).
Clinically important causes
- Acute radiation syndrome
- Acute viral hepatitis
- Addison’s disease
- Atypical pneumonia (mycoplasma)
- Anorexia nervosa
- Chronic pain
- Chronic kidney disease
- Celiac disease
- Common cold
- Congestive heart failure, perhaps due to congestion of the liver with venous blood.
- Crohn’s disease
- Drug addiction
- Foodborne illness
- Hypervitaminosis D
- Hypothyroidism can cause weight gain despite loss of appetite.
- Kidney failure
- Mental disorders, such as depression, bipolar disorder, schizophrenia, etc.
- Metabolic disorders, particularly urea cycle disorders
- Stomach flu
- Sickness behavior
- Superior mesenteric artery syndrome
- Ulcerative colitis
- Zinc deficiency
- Stimulants, such as ephedrine, amphetamine, methamphetamine, MDMA, cathinone, methylphenidate, nicotine, cocaine, caffeine, etc.
- Narcotics, such as heroin, morphine, codeine, hydrocodone, oxycodone, etc.
- Antidepressants can have anorexia as a side effect
- Byetta, a Type II Diabetes drug, will cause moderate nausea and loss of appetite.
- Abrupt cessation of appetite-increasing drugs, such as cannabis and corticosteroids.
- Chemicals that are members of the phenethylamine group. (Individuals with anorexia nervosa may seek them to suppress appetite.)
- Topiramate may cause anorexia as a side effect.
- Other drugs may be used to intentionally cause anorexia in order to help a patient preoperative fasting prior to general anesthesia. It is important to avoid food before surgery to mitigate the risk of pulmonary aspiration, which can be fatal.
- During the post-operative recovery period for a tonsillectomy or adenoidectomy, it is common for adult patients to experience a lack of appetite until their throat significantly heals (usually 10–14 days).
- Altitude sickness
- Significant emotional pain caused by an event (rather than a mental disorder) can cause an individual to temporarily lose all interest in food.
- Experiencing grotesque or unappealing thoughts or conversations, or viewing similar images
- Being in the presence of unappealing things such as waste matter, dead organisms, or bad smells
Sudden cardiac death
Anorexia is a relatively common condition that can lead patients to have dangerous electrolyte imbalances, leading to acquired long QT syndrome which can result in sudden cardiac death. This can develop over a prolonged period of time, and the risk is further heightened when feeding resumes after a period of abstaining from consumption. Care must be taken under such circumstances to avoid potentially fatal complications of refeeding syndrome.
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- Taylor AK, Lebwohl B, Snyder CL, Green PHR (17 September 2015). “Celiac Disease”. GeneReviews®. Retrieved 24 September 2017.
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- Exton, M. S. (1997). “Infection-Induced Anorexia: Active Host Defence Strategy”. Appetite. 29 (3): 369–383. doi:10.1006/appe.1997.0116. PMID 9468766.
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- Home Care After Tonsillectomy and Adenoidectomy
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