31st January 2024

Anorexia Nervosa

Anorexia nervosa is defined by a low body weight for an individual compared to their demographics, and not due to another health condition or due to the unavailability of food. A typical threshold for diagnosis is an adult BMI of 18.5kg/m2, or in adolescents, BMI-for-age of under the 5th percentile. However, this may miss many people in the early stages of the disorder, where psychological treatments are more likely to be effective, and so there is now recognition of rapid weight loss of 20% total body weight within 6 months. Presence of the starvation syndrome is not required to make a diagnosis.

The psychological symptoms can be split into cognitive and behavioural symptoms:

Cognitive symptoms 

• Fear of weight gain
• Body image distortion of seeing themselves as overweight when of a healthy or underweight
• Unrealistic concept of a healthy weight, often with an unachievable goal

These thoughts are overvalued (i.e., difficult to argue, but will show some insight) and obsessive, dominating the person’s thinking. Sometimes fear of being overweight is attributed to other cognitions, e.g., religious fasting, gastrointestinal complaints, or to pursue a more muscular appearance (often seen in men). Cognition drives the behavioural symptoms, which are aimed at reducing energy intake:

• Restricted eating
• Choosing lower calorie foods (or believed lower in calories)
• Slow eating, e.g., playing with food or trying to conceal it from being eaten 
• Purging (e.g., vomiting, laxative use)
• Increasing energy consumption: usually excessive exercise, but can be increasing exposure to cold
• Avoidance of insulin if diabetic
• Use of stimulants and thyroxine 
• Preoccupation with body image will lead to frequent checking behaviours (e.g., weighing frequently, checking in mirrors) or avoidance by wearing loose clothing or getting rid of mirrors at home 

There may be a depressive-type syndrome, often due to the psychological changes caused by starvation – the brain’s response to lack of food is to go into a “power save” mode similar to a mobile phone on low battery, which mimics depression. All these symptoms will often impact social functioning, e.g., being late for work due to checking appearance, causing arguments with friends and family and being unable to function due to poor concentration.