CASC Knowledge Essentials10 · Eating disorders: diagnosis, starvation and medical risk
10 · Eating disorders: diagnosis, starvation and medical risk
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Written by Resident Doctor Committee · Published
10.1 Separate the main syndromes
Syndrome | Core pattern | Distinction |
|---|---|---|
Anorexia nervosa | Significantly low weight, or qualifying rapid loss, maintained by weight-control behaviour; disturbed weight/shape evaluation or failure to recognise low weight as problematic | Can include bingeing and purging |
Bulimia nervosa | Recurrent loss-of-control eating, repeated compensation and excessive importance of weight/shape | Does not meet anorexia criteria |
Binge eating disorder | Recurrent distressing loss-of-control binges | No regular compensation defining bulimia |
ARFID | Restriction causing nutritional, growth or functional consequences | Sensory aversion, low interest or fear of consequences; no drive to change weight/shape |
Anorexia nervosa does not require loss of appetite. Hunger may be present and resisted. Equally, eating a forbidden food is not automatically a binge: loss of control and the episode's pattern matter.
Classification details
For ICD-11 anorexia, adult BMI below 18.5 kg/m² generally indicates significantly low weight. Children need developmental assessment, commonly BMI-for-age below the fifth centile; failure to gain expected weight matters. Exclude a medical explanation or lack of food.
Rapid major loss, for example over 20% in six months, can meet the weight requirement when the rest of the syndrome is present. Adult BMI below 14 is the dangerously low weight specification. These are diagnostic descriptors, not admission thresholds.
Amenorrhoea is no longer required. Nor must the person verbally acknowledge fear of fatness if characteristic behaviour and disturbed weight evaluation are evident.
ICD-11 bulimia: recurrent binge eating and compensatory behaviour, for example weekly for at least one month. A binge involves loss of control while eating notably more or differently than usual; the amount need not be objectively large.
10.2 How anorexia maintains itself
Restriction may initially feel like achievement, control or safety. Starvation then worsens rigidity, concentration, mood and food preoccupation, making change harder. This is why nutrition and psychological treatment belong together.
Genetic vulnerability, temperament, anxiety, adversity, social pressures and development interact. Perfectionism and low self-esteem are common, but neither is essential. Some depressive/obsessional symptoms improve with nutrition; independent depression, OCD or autism-related needs may remain. Autism can affect sensory preferences, routines and treatment accessibility without preventing recovery.
Family therapy does not mean the family caused anorexia. “Anorexogenic family” theories are not a basis for blame. Responses can maintain difficulties, but families are often valuable partners in recovery.
10.3 Starvation physiology: connect the sign to its cause
Finding | Mechanism |
|---|---|
Bradycardia, hypotension, postural symptoms | Low energy intake and reduced cardiovascular reserve; dehydration may contribute |
Cold intolerance, hypothermia, lanugo | Reduced heat production and insulation |
Weakness; difficulty rising from a squat | Muscle loss, sometimes electrolyte disturbance |
Constipation, bloating, early satiety | Slowed GI function; discomfort may persist initially during restoration |
Amenorrhoea, low libido | Reproductive-axis suppression; low sex hormones contribute to bone loss |
Anaemia/other cytopenias | Nutritional and marrow effects; severe illness can blunt inflammatory responses |
Hypoglycaemia | Depleted stores and inadequate glucose availability |
A slow pulse may be malnutrition, not athletic fitness. A normal or raised pulse in a usually bradycardic patient may indicate dehydration, infection or deterioration. A calm, articulate person can still be medically unstable.
Bone health
Undernutrition and hormonal suppression reduce bone density. Adolescents may fail to build peak bone mass. Fractures, prolonged low weight and endocrine suppression remain relevant as weight improves.
Nutritional recovery is fundamental. Calcium or an oral contraceptive alone cannot correct the illness. Periods, fertility and bone density may recover slowly or incompletely; amenorrhoea is not contraception. DXA and hormone/bone treatment depend on age, duration, fracture risk and specialist assessment.
10.4 Why purging is medically dangerous
Compensation can cause harm independently of body weight.
Behaviour | Consequences | Remember |
|---|---|---|
Vomiting | Hypokalaemia, dehydration, metabolic alkalosis, dental erosion, parotid swelling, reflux/oesophageal injury | Gastric acid loss causes alkalosis; secondary renal potassium loss worsens depletion |
Laxatives | Diarrhoea, dehydration, potassium loss; variable acid-base disturbance | Do not reliably remove calories already absorbed in the small intestine |
Diuretics | Volume/electrolyte depletion | Lose water, not fat; potassium effects depend on the drug |
Excessive exercise | Further energy deficit, syncope, injury, cardiovascular stress | Harmful when reserve is inadequate |
Insulin omission | Hyperglycaemia, ketosis, dehydration, ketoacidosis | Can be fatal without low BMI |
Russell's sign is knuckle callus/abrasion from repeated contact with teeth during vomiting. Its absence does not exclude purging. Parotid enlargement is not necessarily infection.
Brushing immediately after vomiting can worsen acid-damaged enamel. Rinse with a non-acidic mouthwash and arrange dental review.
Low potassium causes weakness and arrhythmias. Low magnesium makes potassium harder to replace. QT-prolonging drugs add risk. One normal ECG or electrolyte result cannot establish safety while purging continues.
10.5 What makes an eating disorder a medical emergency?
MEED replaced MARSIPAN. Adult red-flag examples include:
Pulse below 40/min or temperature below 35.5°C.
BMI below 13, or loss exceeding about 1 kg/week for two weeks.
Severe weakness, recurrent syncope, dehydration or organ dysfunction.
Major electrolyte disturbance or hypoglycaemia.
One serious finding can be enough; they need not occur together. Children require age-appropriate assessment.
Severe purging at normal weight, acute food/fluid refusal or deteriorating diabetes can also require hospital care. Combine trajectory with observations, ECG, glucose, potassium, phosphate, magnesium, renal function and ability to maintain intake. Assess suicide and serious self-harm alongside physical risk.
NICE advises against a fixed BMI admission cut-off. The decision is whether medical compromise can be managed safely in the available setting. Medical stabilisation does not imply that all later psychological treatment must be inpatient.
10.6 Refeeding syndrome: the mechanism to remember
Starvation → low insulin → use of fat/protein stores. Total-body phosphate, potassium and magnesium become depleted, even when blood levels initially look normal.
Carbohydrate returns → insulin rises → electrolytes move into cells. Tissue synthesis and energy metabolism increase demand. Sodium/water retention and increased thiamine requirements add to the problem.
Hypophosphataemia is characteristic. Phosphate is needed for ATP, so severe depletion can impair respiratory muscles, myocardium and neurological function. Potassium/magnesium shifts promote arrhythmia; fluid retention can cause oedema and heart failure.
New finding after feeding increases | Concern |
|---|---|
Rapid weight gain and ankle oedema | Fluid retention |
Weakness, dysphagia or breathing difficulty | Phosphate depletion and muscle dysfunction |
Palpitations, collapse, ECG change | Electrolyte-mediated arrhythmia |
Confusion, seizures, reduced consciousness | Metabolic disturbance, thiamine deficiency or another acute illness |
Oedema alone does not establish the syndrome, and phosphate falls have other causes. Interpret the timing, nutritional history, biochemistry and deterioration together.
Avoid refeeding harm and underfeeding harm
Risk rises with severe malnutrition, prolonged low intake, electrolyte depletion and comorbidity. The plan combines nutrition, thiamine/vitamins, electrolyte replacement, glucose checks and fluid/clinical monitoring. A normal baseline phosphate does not exclude a later fall.
MEED uses different regimens according to risk. There is no calorie prescription suitable for every age or presentation: excessive caution can prolong dangerous malnutrition. Feeding and electrolyte correction generally proceed together under an experienced team, modified for severe instability.
10.7 Treatment knowledge for anorexia
Recovery includes nutrition, flexible eating, less preoccupation and restored function. Reaching a weight target is not the same as full recovery.
Group | Psychological treatment |
|---|---|
Adults | CBT-ED, MANTRA or SSCM |
If unsuitable/ineffective | Another recommended approach, including focal psychodynamic therapy where appropriate |
Children/young people | FT-AN; CBT-ED or adolescent-focused psychotherapy if unsuitable/ineffective |
CBT-ED links thoughts, feelings, eating and compensation. MANTRA targets thinking style, emotional/social difficulties and beliefs that make anorexia valuable. SSCM combines supportive work with active nutritional and clinical management.
No medicine replaces nutrition and psychological treatment. Olanzapine may be used off-label by specialists; potential weight gain does not make it a universal treatment. Sedation, metabolic effects and cardiac risk still matter. Treat comorbid depression/OCD where indicated, accounting for starvation-related symptoms and instability.
Early treatment, nutritional improvement and engagement support recovery. Chronic illness, relapse, severe compromise, purging and comorbidity complicate it. Both physical complications and suicide contribute to mortality; older recovery percentages vary too much to predict an individual's outcome.
10.8 Treatment knowledge for bulimia
Restriction → hunger/bingeing → shame/compensation → further restriction. Regular adequate eating interrupts this cycle. Treatment reduces binges and purging; it is not primarily a weight-loss programme.
Adults usually start with bulimia-focused guided self-help. Consider individual CBT-ED if unsuitable or ineffective after about four weeks. Young people usually receive bulimia-focused family therapy, with CBT-ED as an alternative. Treatment addresses restraint, overvaluation of weight/shape and maintaining emotions.
Fluoxetine 60 mg/day is the licensed adult dose alongside psychotherapy to reduce bingeing/purging. It exceeds the usual depression starting dose and is not a universal starting instruction. Remember nausea, sleep disturbance, agitation, sexual dysfunction, interactions and electrolyte risks. A paediatric depression licence is not an adolescent bulimia licence.
Bupropion is contraindicated in current or previous anorexia or bulimia because of seizures, including when prescribed for smoking cessation.
“Multi-impulsive bulimia” is an older description of accompanying self-harm, substance misuse and poorly controlled impulses. It is not a separate current diagnosis or proof of personality disorder.
10.9 Type 1 diabetes and eating disorders
Insulin restriction causes glycosuria and catabolism, producing weight loss but risking ketoacidosis, repeated admissions and accelerated long-term complications. “Diabulimia” is informal; the behaviour can occur within different diagnoses.
Insulin cannot simply be stopped. Diabetes and eating-disorder teams coordinate nutrition, insulin, ketone/glucose checks, fluids and electrolytes. Restoring insulin moves potassium into cells, adding risk in a depleted patient. DKA needs the acute emergency protocol, not an ordinary outpatient glucose-target adjustment.
10.10 Refusal, capacity and compulsory treatment
Anorexia can impair the weighing of food, weight and survival information. Diagnosis alone does not remove capacity; assess the particular decision. A capacitous refusal also does not automatically prevent mental health legislation being used where its criteria apply.
Serious danger can justify compulsory treatment without expressed suicidality. Feeding may constitute treatment of the mental disorder. Authority depends on age, status, capacity and jurisdiction; a parent's request alone cannot authorise an adult's detention or force-feeding. See Chapter 17.