Understanding eating disorders: anorexia, bulimia, and binge eating

Executive overview

No single definition of healthy eating applies to all people — culture, family, and individual biology shape what "normal" eating looks like. Anorexia nervosa is the deadliest psychiatric disorder, not because sufferers lack knowledge of their condition, but because the brain's habit and reward circuits are rewired to drive the disorder unconsciously. Bulimia and binge eating disorder involve the opposite failure: impaired impulse control rather than compulsive restriction.

The core insight: eating disorders are not failures of willpower or knowledge — they are disruptions of homeostatic and reward circuits that override conscious decision-making.

What we know (and don't know) about healthy eating

• No authority — government, clinician, or researcher — can define optimal eating for any individual.
• Useful proxies include liver enzymes, blood lipids, athletic output, mood stability, and gut function.
• Intermittent fasting benefits (improved insulin sensitivity, liver health) are real but modest; total caloric balance remains the dominant factor in weight.
• Cultural context strongly shapes what eating patterns feel normal or disordered.

How hunger and satiety work

• The gut sends two types of signals to the brain: mechanical (stomach volume) and chemical (blood glucose, hormones).
• AGRP neurons in the hypothalamus drive hunger and food-seeking; destroying them eliminates appetite entirely.
• POMC neurons suppress hunger via melanocyte-stimulating hormone.
• Leptin, secreted by body fat, suppresses appetite and enables reproductive function; low leptin shuts off ovulation and sperm production.
• Disrupted leptin signalling is a feature of bulimia and binge eating disorder.
• Evolution hardwired circuits that reward eating fast, often, and in large quantities — food scarcity made this adaptive.

Anorexia nervosa

• Prevalence: 1–2% of women; onset typically in adolescence, diagnosed in early 20s; 10× more common in women than men.
• Rates have been stable for 300–400 years, predating social media — strong biological basis.
• Physical consequences: muscle loss, low heart rate and blood pressure, bone density loss, loss of menstruation, immune disruption.
• Anorexics are not ignorant of caloric content — they are often hyper-accurate fat-content savants, defaulting reflexively to low-fat, low-calorie foods.
• The disorder involves two cognitive features: weak central coherence (missing the big picture, fixating on details) and difficulty in set-shifting (inability to redirect attention away from food classification).
• The brain's reward system is inverted: restricting food generates dopamine release, making restriction feel good rather than punishing.
• Anorexics genuinely perceive themselves as overweight — VR self-avatar studies confirm a measurable visual perceptual distortion, not mere vanity.
• Effective treatment combines habit rewiring (teaching patients to recognise the cues that trigger their restrictive habits) with family-based models (educating the whole family to support without condemning) and pharmacological therapy.
• As habits shift, self-perception distortion also improves — correcting the misperception directly does not work.

Bulimia and binge eating disorder

• Defined by recurrent episodes of overconsumption; bulimia adds purging (vomiting or laxatives); binge eating disorder typically does not.
• Diagnostic threshold: episodes at least once a month over two to three months.
• Unlike anorexia, bulimics feel shame and distress about their behaviour — reward drives them toward food before the episode, not through it.
• Core deficit: lack of inhibitory control — the prefrontal cortex's duration-path-outcome analysis is underactive, the opposite of anorexia.
• Bulimics are hyperimpulsive and frequently show other impulsive behaviours.
• Serotonin-raising drugs (e.g. fluoxetine) and stimulants used for ADHD (e.g. Vyvanse) can restore top-down prefrontal control.
• Behavioural interventions are more effective when started early; drug plus behavioural treatment outperforms either alone.

The knowledge–action gap

• Behaviour is governed by two parallel systems: conscious goal-directed reasoning (duration–path–outcome, prefrontal) and subconscious habits and reflexes (reward and homeostatic circuits).
• In eating disorders, the subconscious system overrides conscious intent — the person can know their behaviour is harmful and still be unable to change it without clinical support.
• Neuroplasticity means deliberate habit change, sustained over time, eventually becomes reflexive — the therapeutic mechanism underlying cognitive behavioural therapy.