Eating Disorders: The Biology and Psychology of Anorexia and Bulimia

Anorexia Nervosa Has the Highest Mortality Rate of Any Psychiatric Disorder

Anorexia nervosa kills approximately 5–10% of those affected over 10 years — a mortality rate that includes both medical complications (cardiac arrhythmias, organ failure, electrolyte disturbances) and suicide, which accounts for roughly 25–50% of eating disorder deaths. These figures exceed those of depression, schizophrenia, and most other serious mental illnesses. The eating disorders — anorexia nervosa, bulimia nervosa, binge eating disorder, and related conditions — affect an estimated 9% of the global population at some point in their lives, predominantly but not exclusively women, and are among the most medically serious and treatment-resistant conditions in psychiatry.

Anorexia Nervosa: Restriction as Control

Anorexia nervosa is characterized by severe caloric restriction leading to low body weight, intense fear of gaining weight, and distorted body image — perceiving oneself as fat despite being significantly underweight. The DSM-5 identifies two subtypes:

The psychological experience of anorexia is not simply a desire to be thin. Research using neuroimaging has identified characteristic patterns: hyperactivity in neural circuits related to threat detection and disgust when viewing food; impaired interoception (awareness of internal body signals including hunger); enhanced cognitive control that in this context is deployed against the body's hunger signals. These neural differences appear to be both trait (present before illness onset) and state (worsened by starvation) characteristics, making recovery neurologically complex.

Medical Consequences of Starvation

The body responds to severe caloric restriction with comprehensive physiological adaptations. When prolonged, these adaptations cross from compensatory to pathological:

• Cardiovascular: Bradycardia (slow heart rate) is present in ~80% of anorexia patients; hypotension; prolonged QT interval on ECG; increased risk of sudden cardiac death; cardiac muscle mass decreases proportionally to skeletal muscle
• Endocrine: Suppression of reproductive hormones causing amenorrhea; elevated cortisol; hypothyroidism; growth hormone resistance; low IGF-1
• Skeletal: Bone density decreases significantly within 6 months of low weight; fracture risk increases; bone loss may be permanent even after recovery
• Neurological: Cortical gray matter volume decreases with malnutrition; partially reversible with weight restoration
• Gastrointestinal: Gastroparesis (delayed stomach emptying); constipation; early satiety that makes refeeding uncomfortable

Bulimia Nervosa: The Binge-Purge Cycle

Bulimia nervosa is defined by recurrent episodes of binge eating (consuming abnormally large amounts of food with a sense of loss of control) followed by compensatory behaviors to prevent weight gain. Unlike anorexia, individuals with bulimia are typically within or above normal weight range — which contributes to under-recognition and late diagnosis.

The binge-purge cycle has a characteristic neurochemical structure. During restriction, food cue salience increases and inhibitory control over eating decreases — both mediated by neural changes including altered opioid and dopamine signaling. Bingeing itself temporarily relieves emotional distress; purging (self-induced vomiting, laxatives, excessive exercise) reduces the anxiety and guilt triggered by the binge. The cycle is self-reinforcing: restriction increases binge risk; bingeing triggers purging; purging enables continued restriction.

Physical consequences of purging include:

• Dental enamel erosion from stomach acid (perimolysis) — characteristic and often irreversible
• Parotid gland enlargement giving a "chipmunk cheek" appearance
• Electrolyte disturbances (particularly hypokalemia from vomiting) — the primary cause of cardiac arrhythmias in bulimia
• Esophageal irritation and, rarely, Mallory-Weiss tears or esophageal rupture from repeated vomiting
• Calloused knuckles (Russell's sign) from using hands to induce vomiting

Risk Factors: Biology, Psychology, and Culture

Eating disorders arise from the interaction of biological vulnerabilities with psychological and sociocultural risk factors:

Evidence-Based Treatments

Treatment approaches differ by disorder type and severity:

For anorexia nervosa: Medical stabilization and weight restoration are the first priority — the malnourished brain is neurologically compromised, making psychotherapy less effective below a threshold weight. Family-based treatment (FBT, also called the "Maudsley approach") has the strongest evidence base for adolescents, temporarily externalizing food decisions to parents until weight restoration enables greater autonomy. No medication reliably treats anorexia's core symptoms, though atypical antipsychotics (olanzapine) may support weight restoration in some patients.

For bulimia nervosa: Cognitive-behavioral therapy specifically adapted for bulimia (CBT-E) is the most evidence-based treatment, targeting the restrictive-binge cycle, food rules, and body image distortion. Interpersonal therapy shows comparable outcomes over longer time horizons. Fluoxetine (Prozac) at 60 mg/day is FDA-approved for bulimia and can reduce binge-purge frequency.

Recovery is achievable but often prolonged. Approximately 50–70% of individuals with bulimia achieve full recovery; full recovery from anorexia is estimated at 30–50%, with many requiring years of treatment and support. Higher duration of illness, lower minimum weight, and older age at onset are associated with poorer outcomes.

This article is for informational purposes only. Consult a qualified healthcare professional for medical advice regarding any health condition.