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# Anorexia nervosa

An eating disorder in which intense fear of weight gain drives severe food restriction and dangerously low weight. It can be fatal but is treatable.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Hypothalamus](https://durgical.com/en/anatomy/hypothalamus/)
- [Pituitary gland](https://durgical.com/en/anatomy/pituitary-gland/)
- [Insula](https://durgical.com/en/anatomy/insula/)
- [Amygdala](https://durgical.com/en/anatomy/amygdaloid-body/)
- [Frontal lobe](https://durgical.com/en/anatomy/superior-frontal-gyrus/)

## Why it happens

- [Severe acute malnutrition: marasmus and kwashiorkor](https://durgical.com/en/general-pathology/severe-acute-malnutrition-marasmus-and-kwashiorkor/)
- [Cachexia, anorexia nervosa and bulimia](https://durgical.com/en/general-pathology/cachexia-anorexia-nervosa-and-bulimia/)
- [Prolonged fasting and starvation](https://durgical.com/en/physiology/prolonged-fasting-and-starvation/)
- [Fed, fasting and starvation states](https://durgical.com/en/biochemistry/topics/fed-fasting-and-starvation-states/)

## What it is

An eating disorder marked by restriction of energy intake leading to a significantly low body weight, an intense fear of gaining weight or behaviour that prevents weight gain, and a disturbed perception of body weight or shape. It has one of the highest mortality rates of any psychiatric disorder.

## Who gets it

Typically begins in adolescence or early adulthood and is much more common in girls and women, although boys and men are also affected and often diagnosed late. It is seen across Latin America, including Colombia, and social pressure toward thinness and social media are recognised contributors.

## Causes

- Genetic predisposition and family history of eating disorders
- Personality traits: perfectionism, rigidity, anxiety
- Sociocultural pressure toward thinness
- Triggers such as dieting, puberty, stress or sports that emphasise weight

## Risk factors

- Female sex and adolescence
- Family history of eating, mood or anxiety disorders
- Perfectionism and obsessive-compulsive traits
- Weight-focused sports or activities (ballet, gymnastics, modelling, endurance running)
- Type 1 diabetes (insulin omission)
- History of bullying about weight or of abuse

## Pathophysiology

Altered reward and anxiety circuits make eating aversive and restriction rewarding, and starvation itself worsens rigid thinking. Energy deficit suppresses the hypothalamic–pituitary–gonadal [axis](https://durgical.com/en/anatomy/axis/) (low GnRH, LH and FSH, causing amenorrhoea), lowers T3 and raises cortisol. The body adapts with slow heart rate, low blood pressure and temperature, and bone loss; purging adds hypokalaemia and metabolic alkalosis.

## Classification

- Restricting type: weight loss by dieting, fasting or excessive exercise
- Binge-eating/purging type: recurrent binge eating or purging (self-induced vomiting, laxatives, diuretics)
- Severity by BMI in adults (mild to extreme) or BMI percentile in children and adolescents

## Symptoms and signs

- Marked weight loss or failure to gain expected weight in children
- Intense fear of weight gain and distorted body image; denial of the seriousness of low weight
- Food rituals, calorie counting and excessive exercise
- Amenorrhoea, cold intolerance, fatigue, dizziness and constipation
- Bradycardia, hypotension, hypothermia, dry [skin](https://durgical.com/en/anatomy/skin/), lanugo hair and brittle nails
- With purging: dental erosion, enlarged parotid glands and calluses on the knuckles (Russell sign)

## Red flags

- Severe bradycardia, hypotension, orthostatic changes or syncope
- Prolonged QTc or arrhythmia on ECG
- Low potassium, phosphate, magnesium or glucose
- Very low BMI or rapid weight loss, or refusal of all food
- Suicidal thoughts

## Diagnosis

**Clinical**
Clinical diagnosis with DSM-5 or ICD-11 criteria: low weight from restriction, fear of weight gain and body-image disturbance. Weight, height, BMI (or percentile in youth), vital signs including orthostatic changes and temperature, and assessment of medical risk and suicide risk. The SCOFF questionnaire is a quick screening tool.

**Tests**
Electrolytes (potassium, phosphate, magnesium), glucose, [kidney](https://durgical.com/en/anatomy/kidney/) and [liver](https://durgical.com/en/anatomy/liver/) function, complete blood count, thyroid function and ECG for bradycardia and QTc. Pregnancy test when relevant.

**Imaging**
Bone densitometry (DXA) after several months of amenorrhoea or low weight, to detect osteopenia or osteoporosis. Brain imaging only when atypical features suggest a hypothalamic lesion.

## Differential diagnosis

- Hyperthyroidism, type 1 diabetes, coeliac disease or inflammatory bowel disease
- Malignancy, tuberculosis or HIV causing weight loss
- Hypothalamic or pituitary tumour
- Major depressive disorder with loss of appetite
- Bulimia nervosa or avoidant/restrictive food intake disorder (ARFID)

## Goal of treatment

Restore weight and normal eating safely, correct medical complications, avoid refeeding syndrome, and treat the distorted thinking about weight and shape to prevent relapse.

## Treatment

**Acute**
Hospital admission for medical instability (bradycardia, hypotension, electrolyte disorders, syncope), very low weight, refusal to eat or suicide risk; feeding is increased gradually.

**Conservative**
Nutritional rehabilitation with a dietitian; family-based treatment is first-line for adolescents.

**Conservative**
Psychotherapy for adults, such as enhanced cognitive behavioural therapy (CBT-E) and other specialist eating-disorder therapies.

**Medical**
No medicine treats anorexia itself; second-generation antipsychotics such as olanzapine are sometimes added for weight gain and obsessive thinking, and coexisting depression or anxiety is treated. Hormonal contraceptives do not protect bone.

**Follow-up**
Nursing care: daily weight under consistent conditions, intake and output, supervised meals and the period after meals (purging), vital signs, and close monitoring of phosphate, potassium and magnesium during the first days of refeeding.

## Complications

- Refeeding syndrome (hypophosphataemia, heart failure, arrhythmia) when nutrition is restarted
- Arrhythmias and sudden cardiac death
- Osteopenia, osteoporosis and fractures
- Hypokalaemia and metabolic alkalosis with purging
- Infertility, delayed puberty and growth failure
- Suicide

## Prognosis

Many patients recover fully, especially with early, specialised treatment in adolescence, but a chronic course is common and relapse is frequent. Mortality from medical complications and suicide is among the highest in psychiatry.

## Prevention

- Early detection in primary care and schools (weight loss, amenorrhoea, food restriction)
- Less weight-focused messages in sport, school and media

## Test yourself

Think of the answer, then tap the question to see it.

## What are the two DSM-5 subtypes of anorexia nervosa?

Restricting type and binge-eating/purging type.

## Which electrolyte falls most characteristically in refeeding syndrome?

Phosphate (hypophosphataemia), often with low potassium and magnesium.

## What is the first-line treatment for adolescents with anorexia nervosa?

Family-based treatment combined with nutritional rehabilitation.

## Why do patients with anorexia develop amenorrhoea?

Energy deficit suppresses hypothalamic GnRH, lowering LH, FSH and oestrogen (functional hypothalamic amenorrhoea).

## Which three vital-sign findings are typical of severe anorexia nervosa?

Bradycardia, hypotension (often orthostatic) and hypothermia.

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## Related conditions

- [Refeeding syndrome](https://durgical.com/en/conditions/refeeding-syndrome/)
- [Osteoporosis](https://durgical.com/en/conditions/osteoporosis/)
- [Hypothyroidism](https://durgical.com/en/conditions/hypothyroidism/)
- [Type 1 diabetes mellitus](https://durgical.com/en/conditions/type-1-diabetes-mellitus/)
- [Graves disease (hyperthyroidism)](https://durgical.com/en/conditions/graves-disease/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Anorexia](https://medlineplus.gov/ency/article/000362.htm) (MedlinePlus (U.S. National Library of Medicine), 2025); [Eating Disorders](https://www.nimh.nih.gov/health/topics/eating-disorders) (National Institute of Mental Health (NIMH), 2024).

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Source: https://durgical.com/en/conditions/anorexia-nervosa/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/anorexia-nervosa/