Anorexia Nervosa is characterized by severe food restriction, intense fear of weight gain, and body image disturbance resulting in significantly low weight. The restrictive type involves caloric restriction and exercise; the binge-eating/purging type involves compensatory behaviors (self-induced vomiting, laxative abuse). Anorexia has serious medical sequelae (cardiac arrhythmias, bone loss, electrolyte imbalance) and the highest mortality rate of eating disorders.
Building on your overview of eating disorders, anorexia nervosa stands apart from other eating pathology in a critical and counterintuitive way: the defining feature is not the eating behavior itself but the cognitive distortion that drives it. A person with anorexia does not primarily experience their restriction as suffering — they experience thinness as necessary, even virtuous, and weight gain as catastrophically threatening. This ego-syntonic quality (the disorder is consistent with how the person sees themselves) distinguishes anorexia from most other mental disorders and explains why it is so resistant to treatment: people do not seek help because they do not experience their behavior as a problem.
The diagnostic triad is worth understanding individually. Caloric restriction or compensatory behaviors (purging, excessive exercise) are the behavioral expressions. Intense fear of weight gain persists even as the person becomes dangerously underweight — the fear does not diminish as weight falls, which differentiates this from rational caloric management. Body image disturbance means the person genuinely perceives their body as larger, fatter, or less acceptable than it appears to others; this is a perceptual and cognitive distortion, not conscious lying. Together, these three features create a self-reinforcing system: the fear motivates restriction, the restriction produces weight loss, the weight loss intensifies the cognitive distortion, and the distortion amplifies the fear.
The medical consequences escalate as the disorder progresses and are directly caused by starvation physiology. The body, depleted of glycogen and fat stores, breaks down muscle for fuel — including cardiac muscle. Bradycardia (abnormally slow heart rate) and arrhythmias reflect cardiac compromise. Bone density falls due to estrogen loss and cortisol elevation. Most critically, electrolyte imbalances — particularly low potassium (hypokalemia) from purging — can trigger fatal cardiac events. The highest mortality rate among psychiatric disorders reflects not only suicide risk but direct medical mortality from starvation.
Treatment is accordingly complex. Medical stabilization (refeeding) is often the first priority, but refeeding itself carries risks (refeeding syndrome: a dangerous shift of phosphate and other electrolytes as the starving body resumes processing carbohydrates). Weight restoration is necessary but not sufficient — the cognitive distortions that drive the behavior persist after weight recovery if not directly targeted. This is why evidence-based approaches combine nutritional rehabilitation with psychotherapy aimed at the distorted beliefs about weight, body, and self-worth, and why family-based treatment (particularly for adolescents) has the strongest evidence base: restructuring the eating behavior environment while the patient's own motivation to change remains compromised.