Anorexia
Specialty	Endocrinology
Symptoms	Not wanting to eat, no hunger, dizziness, weakness

Anorexia is a medical term for a loss of appetite. While the term outside of the scientific literature is often used interchangeably with anorexia nervosa, many possible causes exist for a loss of appetite, some of which may be harmless, while others indicate a serious clinical condition or pose a significant risk.

Anorexia is a symptom, not a diagnosis. Anorexia is not to be confused with the mental health disorder anorexia nervosa. Because the term 'anorexia' is often used as a short-form of anorexia nervosa, to avoid confusion a provider must clarify to a patient whether they are simply referring to a decreased appetite or the mental health disorder. Anyone can manifest anorexia as a loss of appetite, regardless of their sex, age, or weight.

The symptom also occurs in other animals, such as cats,^[1][2] dogs,^[3][4] cattle, goats, and sheep.^[5] In these species, anorexia may be referred to as inappetence. As in humans, loss of appetite can be due to a range of diseases and conditions, as well as environmental and psychological factors.^[2][4]

Etymology

The term is from Ancient Greek: ανορεξία (ἀν-, 'without' + όρεξις, spelled órexis, meaning 'appetite').^[6]

Common manifestations

Anorexia simply manifests as a decreased or loss of appetite. This can present as not feeling hungry or lacking the desire to eat.^[7] Sometimes people do not even notice they lack an appetite until they begin to lose weight from eating less. In other cases, it can be more noticeable, such as when a person becomes nauseated from just the thought of eating. Any form of decreased appetite that leads to changes in the body (such as weight loss or muscle loss) that is not done intentionally as part of dieting is clinically significant.^[8]

Physiology of anorexia

Appetite stimulation and suppression is a complex process involving many different parts of the brain and body by the use of various hormones and signals. Appetite is thought to be stimulated by interplay between peripheral signals to the brain (taste, smell, sight, gut hormones) as well as the balance of neurotransmitters and neuropeptides in the hypothalamus.^[8] Examples of these signals or hormones include neuropeptide Y, leptin, ghrelin, insulin, serotonin, and orexins (also called hypocretins). Anything that causes an imbalance of these signals or hormones can lead to the symptom of anorexia. While it is known that these signals and hormones help control appetite, the complicated mechanisms regarding a pathological increase or decrease in appetite are still being explored.^[8]

Common causes

• Acute radiation syndrome
• Addison's disease
• Alcoholism
• Alcohol withdrawal
• Anemia
• Anorexia nervosa
• Anxiety
• Appendicitis
• Babesiosis
• Benzodiazepine withdrawal
• Bipolar disorder
• Cancer^[9][10]
• Cannabinoid hyperemesis syndrome
• Cannabis withdrawal
• Celiac disease^[11]
• Chronic kidney disease
• Chronic pain
• Common cold
• Constipation
• COPD
• COVID-19
• Crohn's disease
• Dehydration
• Dementia
• Depression
• Ebola
• Fatty liver disease
• Fever
• Food poisoning
• Gastroparesis
• Hepatitis
• HIV/AIDS
• Hypercalcemia
• Hyperglycemia
• Hypervitaminosis D
• Hypothyroidism and sometimes hyperthyroidism
• Irritable bowel syndrome
• Ketoacidosis
• Kidney failure^[12]
• Low blood pressure
• Mania
• Metabolic disorders, particularly urea cycle disorders
• MELAS syndrome
• Nausea
• Opioid use disorder
• Pancreatitis
• Pernicious anemia
• Psychosis
• Schizophrenia
• Side effect of drugs
• Stimulant use disorder
• Stomach flu
• Stress
• Sickness behavior^[13][14]
• Superior mesenteric artery syndrome
• Syndrome of inappropriate antidiuretic hormone secretion^[15]
• Tuberculosis
• Thalassemia
• Ulcerative colitis
• Uremia^[16]
• Folate deficiency
• Vitamin B12 deficiency
• Zinc deficiency
• Infection: 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).^[17]

Complications

Complications of anorexia may result due to poor food intake. Poor food intake can lead to dehydration, electrolyte imbalances, anemia and nutritional deficiencies. These imbalances will worsen the longer that food is avoided.^[8]

Management

Anorexia can be treated with the help of orexigenic drugs.^[20][21]

"Anorexia" vs "anorexic" vs anorexia nervosa

Anorexic can be a description of somebody with the stereotypical thin, frail, malnourished appearance. The appearance is classically associated with anorexia, although in rare cases do patients end up becoming anorexic in appearance. An anorexic or anorectic is also a description given to substances that cause anorexia for weight loss purposes.

Anorexia nervosa is an eating disorder characterized by food restriction due to the strong desire to remain thin. It is considered a mental health diagnosis where people see themselves as obese regardless of their weight or appearance.^[22] The person does not necessarily exhibit anorexia as a symptom in their quest to restrict food intake.^[22]

References