How are the feeding and eating disorders classified?
The main eating disorders are anorexia nervosa, bulimia nervosa and binge eating disorder. The same DSM-5 chapter also covers avoidant or restrictive food intake disorder (ARFID), pica and rumination disorder. Eating disorders are more common in females, and anorexia nervosa typically begins in late adolescence or early adulthood.
| Disorder | Core feature | Body weight |
|---|---|---|
| Anorexia nervosa | Restriction of energy intake, fear of weight gain, disturbed body image | Significantly low |
| Bulimia nervosa | Binge eating followed by inappropriate compensatory behaviour | Often normal, slightly low or high |
| Binge eating disorder | Recurrent binges without compensatory behaviour | Often overweight or obese |
| ARFID | Food restriction with failure to meet nutritional needs; criteria for anorexia nervosa are not met | Often underweight, but does not meet anorexia criteria |
| Pica | Chronic ingestion of non-food substances | Variable |
| Rumination disorder | Repeated regurgitation of food for one month with no other medical cause | Variable |
What are the DSM-5 diagnostic criteria for anorexia nervosa?
Anorexia nervosa is an eating disorder defined by restriction of energy intake relative to requirements, leading to significantly low body weight, with intense fear of gaining weight and a distorted body image. The patient cannot recognise the seriousness of the low weight.
- Criterion A: restriction of energy intake relative to requirements, leading to a significantly low body weight for age, sex, developmental trajectory and physical health.
- Criterion B: intense fear of gaining weight or becoming fat, or persistent behaviour that interferes with weight gain, even at a significantly low weight.
- Criterion C: disturbance in how body weight or shape is experienced, undue influence of weight or shape on self-evaluation, or persistent lack of recognition of the seriousness of the current low weight.
| Subtype | Definition |
|---|---|
| Restricting type | Weight loss through dieting, fasting or excessive exercise; no recurrent binge eating or purging in the last 3 months |
| Binge-eating/purging type | Recurrent binge eating or purging (self-induced vomiting, laxatives, diuretics, enemas) in the last 3 months |
How is severity of anorexia nervosa graded by BMI?
DSM-5 grades the severity of anorexia nervosa in adults by current body mass index (BMI) in kg/m². Studies applying these bands in clinical samples describe them as follows.
| Severity | BMI (kg/m²) |
|---|---|
| Mild | 17 or above |
| Moderate | 16 to 16.99 |
| Severe | 15 to 15.99 |
| Extreme | Below 15 |
Researchers have questioned how well these BMI bands separate patients by eating pathology or impairment, and shape/weight overvaluation has been proposed as an alternative severity marker. For examinations, the BMI bands remain the answer. Atypical anorexia nervosa, classified under other specified feeding or eating disorder, describes patients who meet the criteria but have a BMI above 18.5.
What are the complications and investigations in anorexia nervosa?
Patients report amenorrhoea, cold intolerance, constipation, oedema, fatigue and irritability, and may count calories, purge or exercise compulsively. Complications result from starvation and purging. Basic workup includes full blood count, metabolic panel, coagulation tests, vitamin D, thyroid-stimulating hormone, pregnancy and drug screening, and an ECG to find life-threatening arrhythmias.
| System | Findings |
|---|---|
| Cardiovascular | Bradycardia, hypotension, dilated cardiomyopathy, mitral valve prolapse, pericardial effusion, electrolyte-induced arrhythmias |
| Constitutional | Arrested growth, hypothermia, muscle wasting |
| Dermatologic | Carotenoderma, lanugo, xerosis |
| Endocrine | Hypothalamic hypogonadism, osteoporosis |
| Gastrointestinal | Constipation, gastroparesis |
| Haematologic | Cytopenias including normocytic anaemia, bone marrow hypoplasia |
| Neurologic | Brain atrophy, peripheral neuropathy |
| Renal and metabolic | Hypokalaemic metabolic acidosis (laxatives) or alkalosis (diuretics or vomiting), prerenal failure, refeeding syndrome |
Further studies depend on the case: an echocardiogram for haemodynamic compromise, CT abdomen to exclude superior mesenteric artery syndrome when BMI is below 14, and DEXA after more than 9 months of amenorrhoea. Anorexia nervosa has one of the highest mortality rates among eating disorders because of medical complications, substance abuse and suicide.
What are the diagnostic criteria and findings in bulimia nervosa?
Bulimia nervosa involves episodes of binge eating (eating an amount definitely larger than most people would in a similar period, usually under 2 hours, with loss of control) followed by inappropriate compensatory behaviour to prevent weight gain: self-induced vomiting, laxative or diuretic misuse, extreme exercise or fasting. Binge eating and compensation both occur on average at least once a week for three months, and self-evaluation is unduly influenced by body shape and weight. The disturbance does not occur only during episodes of anorexia nervosa.
| Domain | Findings |
|---|---|
| Examination | Parotid gland swelling, dental erosion, hypotension, dry skin, calluses on the back of the hand (Russell sign) |
| Laboratory | Hypokalaemia, hypokalaemic hypochloraemic metabolic alkalosis, hyponatraemia, transaminitis |
| Drug treatment | Fluoxetine is the only FDA-approved drug; 60 mg is better than placebo for reducing binge and vomiting frequency. Bupropion must be avoided because of seizure risk |
| Psychotherapy | Cognitive-behavioural therapy and interpersonal psychotherapy show benefit |
How does binge eating disorder differ from bulimia nervosa?
Binge eating disorder is characterised by recurrent episodes of eating unusually large amounts of food with a sense of lost control, without the compensatory behaviours of bulimia nervosa. The binge eating occurs on average at least once a week for three months with marked distress. Patients are often overweight or obese, and the condition affects 25 to 30 per cent of patients seeking obesity treatment.
- Cognitive-behavioural therapy is first-line psychotherapy.
- Lisdexamfetamine is FDA-approved for moderate to severe binge eating disorder and produces both behavioural improvement and weight loss.
- Features include eating alone from embarrassment and feeling disgusted, depressed or guilty afterwards.
What is refeeding syndrome and who is at risk?
Refeeding syndrome is the group of medical complications caused by fluid and electrolyte shifts when nutrition is restarted after prolonged starvation. Hypophosphataemia is its hallmark, with hypokalaemia, hypomagnesaemia and thiamine deficiency also seen. It occurs commonly in patients with eating disorders, but also with chronic alcoholism, malabsorption, chronic malnutrition, poorly controlled diabetes and after surgery.
Feeding raises glucose, which stimulates insulin. Insulin drives phosphate and potassium into cells while stores are already depleted, and glucose phosphorylation uses phosphate to make ATP. Low phosphate reduces 2,3-DPG, shifting the oxygen-haemoglobin curve to the left and limiting oxygen release to tissues; it also weakens cardiac and respiratory muscle. Thiamine requirements rise with glucose metabolism, so deficiency can cause Wernicke and Korsakoff syndromes and cardiac dysfunction. Low magnesium and potassium both promote torsades de pointes.
| Category | Criteria |
|---|---|
| One or more of | BMI below 16 kg/m²; unintentional weight loss over 15 per cent in 3 to 6 months; little or no intake for over 10 days; low potassium, phosphate or magnesium before feeding |
| Two or more of | BMI below 18.5 kg/m²; unintentional weight loss over 10 per cent in 3 to 6 months; little or no intake for over 5 days; history of alcohol misuse or drugs including insulin, chemotherapy, antacids or diuretics |
How are eating disorders and refeeding managed?
Anorexia nervosa treatment centres on nutritional rehabilitation and psychotherapy. Family-based therapy benefits paediatric patients. Inpatient care is needed for medical instability (bradycardia, dehydration, hypoglycaemia, electrolyte abnormalities, hypothermia, hypotension), high suicide risk, persistent severe purging, a need for supervised or nasogastric feeding, or severe anorexia such as under 70 per cent of ideal body weight. Pharmacotherapy is not used initially; olanzapine is first-line for acutely ill patients who do not respond. SSRIs plus therapy suit non-acutely ill patients with comorbid depression or anxiety, tricyclics are less preferred because of cardiotoxicity, and bupropion is contraindicated because of seizure risk.
| Element | Recommendation |
|---|---|
| Starting energy | Maximum 10 kcal/kg/day, rising slowly to meet or exceed full needs by 4 to 7 days |
| Extreme cases | 5 kcal/kg/day (for example BMI below 14 or negligible intake for more than 15 days) |
| Monitoring | Continuous cardiac rhythm monitoring in those with arrhythmias; restore circulatory volume and monitor fluid balance |
| Thiamine and vitamins | Oral thiamine 200 to 300 mg daily, vitamin B co strong 1 or 2 tablets three times a day and a multivitamin or trace element supplement daily, immediately before and during the first 10 days of feeding |
| Electrolytes | Potassium 2 to 4 mmol/kg/day, phosphate 0.3 to 0.6 mmol/kg/day, magnesium 0.2 mmol/kg/day intravenously or 0.4 mmol/kg/day orally, unless pre-feeding levels are high |
What are the common traps in eating-disorder questions?
- Amenorrhoea is not a DSM-5 criterion for anorexia nervosa.
- Bulimia nervosa threshold is once weekly for three months, not twice weekly.
- Russell sign, parotid swelling and dental erosion point to bulimia nervosa (vomiting).
- Fluoxetine is the approved drug in bulimia; bupropion is avoided in both anorexia and bulimia.
- Hypophosphataemia is the hallmark of refeeding syndrome and thiamine is given before feeding.
- Normal-weight binge-purging patient = bulimia nervosa; low-weight binge-purging patient = anorexia nervosa, binge-eating/purging type.
- BMI bands: mild 17 or more, moderate 16 to 16.99, severe 15 to 15.99, extreme below 15.