Anorexia nervosa is thought to result from psychological, biological, and societal stresses involving sexual development at puberty. There is a high incidence of premorbid anxiety disorder in prepubescent patients who subsequently develop anorexia nervosa. The patient's altered body image results in a perception of fatness. Attempts to correct this flaw through food restriction or progressive purging lead to progressive starvation. Modern preoccupation with slenderness and beauty in the Western world may contribute to the mindset of slenderness as a valued quality in adolescents.
Subsequent malnutrition leads to protein deficiency and disruption of multiple organ systems.
Other nutritional deficiencies may appear, including hypoglycemia, severe loss of fat stores, and multiple vitamin deficiencies. It is unclear what neurotransmitter systems are involved, although endogenous opioids, cortisol, and norepinephrine abnormalities have been proposed to contribute to the condition. No studies have demonstrated a consistent improvement with neurotransmitter manipulation. Neuroendocrine disturbances include delayed puberty, amenorrhea, anovulation, low estrogen states, decreased somatomedin C and increased growth hormone, euthyroid sick state, decreased antidiuretic hormone, hypercarotenemia, neuropathy, myopathy, encephalopathy, and hypothermia. Decreased gonadotropin levels and hypogonadism may occur among afflicted males.