Definition and epidemiology
Anorexia nervosa (AN) is a psychiatric eating disorder defined by self-imposed caloric restriction resulting in a body weight significantly below what is expected for age, sex, and developmental trajectory, combined with an intense fear of gaining weight and a disturbance in how body weight or shape is experienced.
- Lifetime prevalence is approximately 0.5-1% in women and roughly 10 times lower in men.
- Typical onset is in adolescence, with peaks around ages 14-18, though presentations in children and adults also occur.
- Female-to-male ratio is roughly 10:1, though male and non-binary cases are increasingly recognized and may be underdiagnosed.
- It has the highest mortality rate among psychiatric disorders, from both medical complications (cardiac arrhythmia, electrolyte disturbance) and suicide.
- Higher prevalence is seen in industrialized countries and in activities emphasizing leanness (ballet, gymnastics, modeling, wrestling).
- AN has the highest mortality rate of any psychiatric disorder.
- Bradycardia and hypotension reflect a hypometabolic starvation adaptation.
- Refeeding syndrome: watch phosphate, potassium, magnesium when reintroducing calories.
- Amenorrhea results from hypothalamic suppression of LH/FSH, not a diagnostic requirement in DSM-5.
- Family-based therapy is first-line for adolescents; CBT-E for adults.
- No drug is approved to treat core anorexia; low-dose olanzapine is sometimes adjunctive.
- Lanugo hair and parotid swelling are classic exam findings.
- Distinguish from ARFID: ARFID lacks fear of weight gain or body image disturbance.
Etiology and risk factors
The etiology is multifactorial, involving genetic, neurobiological, psychological, and sociocultural contributions.
Risk factors
- Female sex and adolescence/young adulthood.
- Family history of eating disorders, depression, or substance use.
- Personal traits: perfectionism, obsessionality, high anxiety, low self-esteem.
- Participation in weight-sensitive sports or professions (gymnastics, ballet, wrestling, modeling).
- Sociocultural pressure toward thinness and weight-related teasing or bullying.
- History of childhood trauma or sexual abuse (nonspecific but increases risk).
- Type 1 diabetes mellitus (insulin omission used for weight control, sometimes termed "diabulimia").
Pathophysiology
Chronic caloric restriction produces a hypometabolic state as the body adapts to starvation, affecting nearly every organ system.
- Endocrine: Hypothalamic-pituitary-gonadal axis suppression causes functional hypothalamic amenorrhea, low LH/FSH, and low estrogen; growth hormone resistance and low IGF-1 contribute to bone loss; sick euthyroid pattern (low T3) conserves energy.
- Cardiovascular: Loss of cardiac muscle mass, bradycardia, hypotension, and QT prolongation increase arrhythmia risk.
- Skeletal: Low estrogen plus relative energy deficiency causes decreased bone mineral density and increased fracture risk (female athlete triad overlap).
- Hematologic: Bone marrow hypoplasia can cause anemia, leukopenia, and thrombocytopenia.
- Metabolic: Starvation shifts metabolism toward fat and protein breakdown; purging behaviors (if present) cause hypokalemic, hypochloremic metabolic alkalosis.
- Refeeding risk: Chronic starvation depletes intracellular phosphate; reintroducing carbohydrates triggers an insulin surge that drives phosphate, potassium, and magnesium into cells, risking refeeding syndrome.
Clinical features
Presentation combines physical signs of starvation with characteristic cognitive and behavioral features.
Core features
- Restriction of energy intake leading to significantly low body weight.
- Intense fear of weight gain or persistent behavior that interferes with weight gain, despite being underweight.
- Disturbance in self-perceived body weight or shape, or denial of the seriousness of low body weight.
Physical signs
- Emaciation, lanugo (fine downy body hair), dry skin, brittle hair and nails.
- Bradycardia, hypotension, hypothermia, orthostatic symptoms.
- Parotid gland swelling and dental erosion if self-induced vomiting is present.
- Amenorrhea or irregular menses (no longer a required diagnostic criterion but commonly present).
Behavioral features
- Food rituals, calorie counting, excessive exercise, denial of hunger.
- Social withdrawal, especially around meals.
- Two subtypes: restricting type (dieting/exercise only) and binge-eating/purging type (recurrent binge eating and/or purging).
Diagnosis
Diagnosis is clinical, based on history, physical exam, and exclusion of other causes of weight loss, supported by DSM-5 criteria.
DSM-5 criteria (summary)
- Restriction of energy intake relative to requirements, leading to significantly low body weight.
- Intense fear of gaining weight or persistent behavior interfering with weight gain.
- Disturbance in body image or denial of the medical seriousness of low weight.
Workup
| Test | Purpose |
|---|---|
| CBC | Anemia, leukopenia from marrow suppression |
| Electrolytes, phosphate, magnesium | Baseline and refeeding syndrome risk |
| ECG | Bradycardia, QT prolongation |
| TSH, LH/FSH, estradiol/testosterone | Rule out other causes, assess hypothalamic suppression |
| Bone density (DEXA) | If amenorrhea greater than 6-12 months |
- Severity (DSM-5) is graded by BMI (mild, moderate, severe, extreme) in adults.
- Collateral history from family is often essential, since insight is frequently limited.
Differential diagnosis
- Bulimia nervosa: binge-purge cycles without the sustained low body weight criterion.
- Avoidant/restrictive food intake disorder (ARFID): restriction without fear of weight gain or body image disturbance.
- Major depressive disorder: appetite loss and weight loss but without body image distortion.
- Hyperthyroidism: weight loss with increased appetite, tachycardia rather than bradycardia.
- Inflammatory bowel disease, celiac disease, malignancy: organic causes of weight loss, usually without fear of weight gain.
- Addison disease: weight loss, hypotension, but with hyperpigmentation and hyperkalemia.
- Type 1 diabetes mellitus: weight loss with polyuria/polydipsia and hyperglycemia.
Management
Treatment requires a multidisciplinary team (medical, nutritional, psychiatric) and focuses on weight restoration plus psychotherapy.
Medical stabilization
- Hospitalize if severe bradycardia, electrolyte derangement, syncope, BMI critically low, or suicidality.
- Gradual, supervised refeeding with close monitoring of phosphate, potassium, and magnesium to prevent refeeding syndrome; thiamine supplementation is often given before/with refeeding.
Psychotherapy (first-line)
- Family-based therapy (Maudsley approach) is first-line for adolescents, with strong guideline support (NICE, APA).
- Cognitive behavioral therapy (CBT-E) and specialist supportive clinical management are preferred for adults.
Pharmacotherapy
- No medication is approved specifically to treat the core restriction/weight-gain refusal of AN.
- Olanzapine (low-dose, off-label) may help weight gain and reduce anxiety/obsessionality in some guidelines (APA notes modest evidence).
- SSRIs do not treat acute anorexia effectively but may help comorbid depression/anxiety once weight is partially restored.
- Guideline consensus (APA, NICE) agrees psychotherapy and nutritional rehabilitation are central; pharmacotherapy is adjunctive only.
Monitoring
- Regular weight, electrolytes, ECG, and bone density assessment during recovery.
Complications and prognosis
- Cardiac: arrhythmia, QT prolongation, sudden cardiac death — the leading cause of AN-related mortality.
- Osteoporosis and increased fracture risk from prolonged estrogen deficiency.
- Infertility and menstrual irregularity from hypothalamic suppression.
- Refeeding syndrome: hypophosphatemia, hypokalemia, hypomagnesemia, fluid overload, cardiac failure during early nutritional treatment.
- Suicide: markedly elevated risk, contributing to AN having the highest mortality of any psychiatric disorder.
- Prognosis is variable: roughly half of patients achieve full recovery, a third show partial improvement, and a subset develop a chronic, relapsing course; early intervention improves outcomes.
SCOFF screening questionnaire: Sick (make yourself vomit), Control (loss of control over eating), One stone (lost over 14 lb/6.4 kg in 3 months), Fat (believe you are fat when others say you are thin), Food (food dominates your life) — 2 or more "yes" answers suggests an eating disorder warranting further assessment.
Practice questions
1. A 16-year-old girl is brought in by her mother for a 20-lb weight loss over 6 months. She exercises for 2 hours daily, eats only salads, and insists she is "still too fat" despite a BMI of 15.5 kg/m2. Vital signs show HR 48/min and BP 88/56 mmHg. Which of the following is the most appropriate first-line treatment?
2. A 19-year-old woman with anorexia nervosa is admitted for severe malnutrition (BMI 13 kg/m2) and started on a structured refeeding plan. Two days into refeeding, she develops confusion, muscle weakness, and new peripheral edema. Which electrolyte abnormality is most likely responsible?
3. A 22-year-old woman with a 3-year history of anorexia nervosa has not menstruated for 18 months. Which of the following best explains her amenorrhea?
Frequently asked questions
What causes anorexia nervosa?
Anorexia nervosa results from an interplay of genetic predisposition, neurobiological vulnerability, personality traits like perfectionism and anxiety, and sociocultural pressure toward thinness. There is no single cause; family history of eating disorders or mood disorders, participation in weight-sensitive activities, and adolescent-onset stress often contribute. It is not caused simply by dieting choice or vanity.
What are the first signs of anorexia?
Early signs include noticeable weight loss, skipping meals, excessive calorie counting, rigid food rules, increased exercise, and social withdrawal around mealtimes. Physical clues can include feeling cold, fatigue, and in females, irregular or absent periods. Family members often notice behavioral changes before the person acknowledges a problem.
How is anorexia nervosa diagnosed?
Diagnosis is clinical, using DSM-5 criteria: restricted intake causing significantly low body weight, intense fear of weight gain, and body image disturbance or denial of the problem's seriousness. Clinicians also obtain labs, an ECG, and sometimes bone density scans to assess medical severity and rule out organic causes of weight loss.
Is anorexia nervosa curable?
Yes, many people recover fully, especially with early treatment; roughly half of patients achieve full recovery, a third improve substantially, and a smaller group develop a chronic course. Treatment combining nutritional rehabilitation and psychotherapy, such as family-based therapy or CBT, gives the best outcomes, particularly when started early in adolescence.
Anorexia nervosa vs bulimia nervosa — what is the difference?
Anorexia nervosa involves sustained restriction leading to significantly low body weight, while bulimia nervosa involves recurrent binge eating followed by compensatory behaviors (vomiting, laxatives, excessive exercise) in a person who is typically normal weight or overweight. Some anorexia patients also binge/purge (binge-eating/purging subtype), but the defining feature separating the two diagnoses is the presence of significantly low body weight.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: F50.0
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.