What eating disorder might explain irregular menses in an adolescent with a fear of gaining weight and poor caloric intake?

Anorexia nervosa is characterized by an intense fear of gaining weight, drastic restriction of caloric intake, and a distorted body image. Adolescents suffering from this disorder often exhibit symptoms like significant weight loss and an abnormal preoccupation with food, dieting, and body shape. One of the physiological effects of such excessive weight loss and malnutrition is the disruption of menstrual cycles, leading to irregular menses or amenorrhea. This occurs because the body, in response to inadequate nutrition, conserves energy by reducing non-essential functions, such as reproductive hormones.

This aligns with the symptoms described in the question, emphasizing the relationship between extreme caloric restriction and menstrual irregularities in adolescents. Other eating disorders listed, such as bulimia, orthorexia, and binge eating disorder, do not primarily encompass the same severity of weight loss and restrictive behaviors that lead to the hormonal changes associated with anorexia nervosa. Therefore, anorexia nervosa is the most appropriate diagnosis in this context, as it explains both the fear of weight gain and the poor nutritional intake linked to irregular menstrual cycles.