Eating Disorders

Eating disorders are psychiatric conditions involving an unhealthy and distorted obsession with body image and food. The main types are:

  • Anorexia nervosa
  • Bulimia nervosa
  • Binge eating disorder


Eating disorders are more common in females and young people.


Anorexia Nervosa

With anorexia nervosa, the person feels they are overweight despite evidence of normal or low body weight. It involves obsessively restricting calorie intake to lose weight. Often, the person exercises excessively and may use diet pills or laxatives to limit the absorption of food.

Features of anorexia nervosa include:

  • Weight loss (e.g., 15% below expected or BMI less than 17.5)
  • Amenorrhoea (absent periods)
  • Lanugo hair (fine, soft hair across most of the body)
  • Hypotension (low blood pressure)
  • Hypothermia (low body temperature)
  • Mood changes, including anxiety and depression


Amenorrhea (absence of periods) occurs due to disruption of the hypothalamic-pituitary-gonadal axis. There is a lack of gonadotrophins (LH and FSH) from the pituitary, leading to reduced activity of the ovaries (hypogonadism).

Cardiac complications include arrhythmia, cardiac atrophy and sudden cardiac death. Low bone mineral density is another complication.

Anorexia nervosa has the highest mortality of any psychiatric condition.


Bulimia Nervosa

Unlike anorexia, people with bulimia often have a normal body weight. Their body weight tends to fluctuate. The condition involves binge eating, followed by purging by inducing vomiting or taking laxatives to prevent the calories from being absorbed.

Features of bulimia nervosa include:

  • Erosion of teeth
  • Swollen salivary glands
  • Mouth ulcers
  • Gastro-oesophageal reflux
  • Calluses on the knuckles where they have been scraped across the teeth (called Russell’s sign)


Alkalosis can occur after repeated vomiting of hydrochloric acid from the stomach.

TOM TIP: Unique examination findings in bulimia make it a popular spot diagnosis in exams. A teenage girl with an average body weight that presents with swelling to the face or under the jaw (salivary glands), calluses on the knuckles and alkalosis on a blood gas may indicate bulimia. The presenting complaint may be abdominal pain or reflux.


Binge Eating Disorder

Binge eating disorder is characterised by episodes where the person excessively overeats, often as an expression of underlying psychological distress. The person typically feels a loss of control. It is not a restrictive condition like anorexia or bulimia, and patients are likely to be overweight.

Binges may involve:

  • A planned binge involving “binge” foods
  • Eating very quickly
  • Unrelated to feelings of hunger
  • Becoming uncomfortably full
  • Eating in a dazed state


Blood Results

Possible blood test findings in restrictive eating disorders include:

  • Anaemia (low haemoglobin)
  • Leucopenia (low white cell count)
  • Thrombocytopenia (low platelets)
  • Hypokalaemia (low potassium – due to vomiting or excessive laxatives)


Reduced bone marrow activity causes normocytic normochromic anaemia, leucopenia (with low neutrophils and low lymphocytes) and thrombocytopenia.



Eating disorders can be challenging to manage and will involve specialist services and a multidisciplinary team. Particularly with anorexia nervosa, the patient may not recognise the need or be motivated to treat the condition.

Management is centred around changing behaviour and addressing environmental factors:

  • Self-help resources
  • Psychological therapies (e.g., cognitive behavioural therapy)
  • Addressing other psychosocial factors, such as depression, anxiety and relationships


Severe cases may require compulsory admission for observed refeeding and monitoring for refeeding syndrome.


Refeeding Syndrome

Refeeding syndrome occurs when someone with an extended severe nutritional deficit resumes eating. The lower the BMI and the longer the period of malnutrition, the higher the risk. It should be suspected in anyone with minimal nutritional intake for more than five da

During prolonged starvation, intracellular potassium, phosphate and magnesium are depleted. These electrolytes move from inside the cells to the blood to maintain normal serum levels in the absence of dietary intake. Cell metabolism reduces to conserve energy, resulting in a loss of intracellular electrolytes. For example, the action of the sodium/potassium ATP-pump slows, which normally pumps potassium into the cell and sodium out of the cell.

During refeeding, various mechanisms shift magnesium, potassium and phosphate out of the blood and sodium into the blood. Carbohydrate intake causes an increase in insulin, which drives glucose, potassium and phosphate into cells. The sodium/potassium ATP-pump actively pumps potassium into the cells and sodium out of the cells. Insulin causes extra sodium reabsorption in the kidneys. The overall effects are:

  • Hypomagnesaemia (low serum magnesium)
  • Hypokalaemia (low serum potassium)
  • Hypophosphataemia (low serum phosphate)
  • Fluid overload (due to water following the extra sodium into the extracellular space)


There is a risk of arrhythmia and heart failure. Rarely, it can be fatal.

Management will be according to the local protocol under specialist supervision:

  • Slowly reintroducing food with limited calories
  • Magnesium, potassium, phosphate and glucose monitoring
  • Fluid balance monitoring
  • ECG monitoring in severe cases
  • Supplementation with electrolytes and vitamins, particularly B vitamins and thiamine


Last updated June 2024
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