Nursing care
Anorexia nervosa vs bulimia nervosa: weight, purging signs and medical risk
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated October 2026
Short answer
Body weight is the most differentiating cue. Anorexia nervosa involves restriction leading to significantly low weight, with bradycardia, hypotension and refeeding risk. Bulimia nervosa involves recurrent binge eating and compensatory purging in someone usually of normal or higher weight. Both can cause dangerous low potassium and heart rhythm problems, which shape nursing priorities.
Start with weight, then ask about behaviours
Anorexia nervosa is defined by restriction of intake leading to significantly low body weight, with intense fear of gaining weight and a distorted view of body shape. It has a restricting type and a binge-eating and purging type, so vomiting does not on its own mean bulimia. Low weight is the feature that keeps the diagnosis as anorexia.
Bulimia nervosa involves recurrent episodes of binge eating followed by compensatory behaviour such as self-induced vomiting, laxative misuse, fasting or excessive exercise, at least weekly over months. Weight is usually normal or above normal, so the illness can be hidden. Shame and secrecy around eating are common in both disorders. Because weight may look reassuring, purging can go unnoticed until complications appear.
Physical findings that point each way
Starvation in anorexia slows the body: bradycardia, orthostatic hypotension, low temperature, fine lanugo hair, oedema and absent periods are typical. Prolonged QT interval and electrolyte disturbance can predispose to dangerous arrhythmias and sudden cardiac death. Severe or rapid weight loss is one reason for hospital admission. Purging in the binge-purge type adds low potassium and sodium to these risks.
Repeated vomiting leaves its own marks: enlarged salivary glands, dental enamel erosion and calluses on the knuckles from inducing vomiting, known as Russell sign. Purging can drop potassium enough to trigger arrhythmias, and oesophageal or gastric rupture, though rare, is life threatening. People with binge-purge anorexia may show these signs too.
Refeeding risk belongs mainly to anorexia
When a severely malnourished patient starts eating again, shifts of phosphate, potassium and magnesium into cells can cause refeeding syndrome, with hypophosphataemia as a hallmark. It can lead to heart failure, arrhythmia and confusion. Nutrition is restored gradually under a prescribed plan, and electrolytes, weight, fluid balance and heart rhythm are monitored closely. Risk is greatest in the first days of nutritional restoration.
Report falling phosphate or potassium, new oedema, breathlessness, palpitations or confusion during the early days of refeeding. Weigh the patient consistently, using the same scale and clothing according to the unit's protocol. Supervised meals and observation after eating are commonly used to support intake and reduce concealed restriction or purging.
Nursing priorities and treatment for each disorder
In anorexia, physical stabilisation comes first: monitor vital signs including orthostatic changes, cardiac rhythm and electrolytes, and follow the nutrition plan. Family-based treatment is used for adolescents, and psychotherapy supports adults. Build trust with a consistent, non-judgemental approach that focuses on health rather than arguing about appearance. Olanzapine is sometimes used to help weight gain, but it does not replace nutrition and psychotherapy.
In bulimia, check potassium and heart rhythm, assess for dehydration and dental damage, and supervise the period after meals as the plan directs. Cognitive behavioural therapy is the first-line treatment, and fluoxetine can reduce binge and purge frequency but works best alongside therapy. In both disorders, ask about self-harm and suicidal thoughts. Encourage dental review and gentle mouth rinsing advice as the dental team recommends.
Worked scenario: which client is at greatest medical risk?
Picture four hypothetical clients. One has bulimia with stable weight and dental erosion. One has anorexia, a heart rate of 38 and dizziness on standing, starting her second day of refeeding with a falling phosphate. One has body image concerns without abnormal vital signs. One has bulimia and asks about therapy options. The refeeding client is the priority. Look first for the abnormal vital signs and laboratory values.
Her bradycardia, orthostatic symptoms and dropping phosphate signal immediate cardiac and refeeding danger. The bulimia client would rise in priority if her potassium were very low or she reported palpitations. The exam is testing whether you weigh physiological instability over the psychological features that both disorders share.
Sources and further reading
MSD Manual Professional: Anorexia Nervosa. Low body weight, restricting and binge-purge types, bradycardia, hypotension, lanugo, QT prolongation, electrolyte risk, refeeding hypophosphataemia, admission and treatment.
MSD Manual Professional: Bulimia Nervosa. Normal or above-normal weight, binge-purge cycle, salivary gland swelling, enamel erosion, Russell sign, hypokalaemia, oesophageal rupture, CBT and fluoxetine.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our mental health practice questions are the closest set to what this page covers.
Common questions
Can someone with anorexia nervosa also vomit after eating?
Yes. Anorexia has a binge-eating and purging type. Significantly low body weight keeps the diagnosis as anorexia even when purging occurs.
Why is potassium so important in bulimia?
Repeated vomiting or laxative misuse can lower potassium enough to cause dangerous heart rhythm problems. Monitoring electrolytes and the ECG is a priority.
What is refeeding syndrome?
It is a dangerous shift of electrolytes, especially phosphate, when a severely malnourished person begins eating again. It can cause heart failure, arrhythmia and confusion, so refeeding is gradual and closely monitored.
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