Physiological Responses to Anorexia Nervosa: The Body's Starvation Adaptations

Anorexia nervosa is a severe psychiatric disorder characterized by relentless restriction of energy intake, intense fear of weight gain, and a distorted body image. In response to prolonged starvation, the body activates a cascade of survival mechanisms that, while initially protective, become profoundly pathological and life-threatening.

Metabolic Downregulation: "Starvation Mode"

Basal metabolic rate plummets by up to 30–50%. The body conserves energy by reducing core temperature (hypothermia), heart rate (bradycardia), and blood pressure (hypotension), leading to fatigue, cold intolerance, dizziness, and syncope.

Endocrine Disruption

The hypothalamic-pituitary-gonadal axis is suppressed, causing hypogonadotropic hypogonadism: amenorrhea in females, low testosterone in males. Growth hormone resistance and low IGF-1 impair bone formation, leading to osteopenia/osteoporosis. Thyroid function shifts to a "sick euthyroid" pattern (low T3, normal/low T4).

Catabolism of Lean Mass

Muscle protein—including cardiac muscle—is broken down for gluconeogenesis. This causes weakness, atrophy, and potentially fatal cardiomyopathy with arrhythmias.

Integumentary Changes

Energy is diverted from non-essential structures: hair thins and falls out (telogen effluvium), nails become brittle, skin turns dry and scaly. Lanugo—fine, downy hair—may appear on the face and body as a thermal adaptation.

Gastrointestinal Slowing

Reduced gut motility leads to constipation, bloating, and gastroparesis. Refeeding after prolonged starvation risks refeeding syndrome—dangerous shifts in electrolytes (especially phosphate) and fluid balance.

Electrolyte and Fluid Chaos

Purging behaviors (vomiting, laxatives) compound starvation-induced losses. Hypokalemia, hyponatremia, and hypomagnesemia precipitate cardiac arrhythmias, seizures, and muscle breakdown (rhabdomyolysis).

Multiorgan Failure

In extreme, prolonged cases, the cumulative insult leads to renal, hepatic, and cardiac failure.

Critical reminder: These are maladaptive survival responses, not healthy weight management. Anorexia nervosa has the highest mortality rate of any psychiatric illness. Early, multidisciplinary treatment (medical, nutritional, psychological) saves lives.