Physiology of Anorexia Nervosa
and Bulimia Nervosa
KATHERINE A. HALMI
Most physiological abnormalities present in patients with anorexia nervosa and bulimia nervosa are secondary to an underweight state, dieting, or behavior directed toward losing weight, such as self-induced vomiting, laxative misuse, and excessive exercising. With nutritional rehabilitation and cessation of weight-losing behaviors, the physiological changes are reversed. Medical complications of anorexia nervosa and bulimia nervosa are described in Chapter 50.
Endocrine changes in anorexia nervosa and bulimia nervosa involve the hypothalamic– pituitary–ovarian, adrenal, and thyroid axes, as well as growth hormone, insulin, neuropeptides, endogenous opioids, leptin, and neurotransmitters. (See Chapter 49 for a description of neurotransmitter abnormalities.)
Amenorrhea is an essential clinical feature in the diagnosis of anorexia nervosa. In underweight patients, basal levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estrogen are decreased. The 24-hour LH secretion pattern is abnormal and similar to that found in prepubertal females. With weight restoration, normal LH secretion occurs in most patients. The return of normal menstrual cycles lags behind, with resumption associated with psychological improvement and cessation of dietary restriction. Regular injections of gonadotropin-releasing hormone (GnRH) in underweight patients produce ovulation. These findings suggest that the pituitary cells producing LH and FSH are understimulated due to hyposecretion of GnRH in the hypothalamus. Dysfunction in the neurotransmitter systems that influence GnRH release is most likely present in anorexia nervosa.
Menstrual irregularities occur in many women with bulimia nervosa. Intermittent di-