A characteristic symptom of anorexia nervosa is:

Amenorrhea, or the absence of menstruation, is a characteristic symptom of anorexia nervosa. This condition often arises due to significant weight loss and a severely restricted caloric intake, which disrupt the hormonal balance necessary for maintaining regular menstrual cycles. The low body weight and nutritional deficiencies associated with anorexia can lead to various physiological changes, including the cessation of menstruation.

In contrast, increased appetite, a puffy face, and frequent overeating are not typical symptoms associated with anorexia nervosa. Increased appetite would typically contradict the behaviors seen in individuals with this disorder, who often exhibit aversion to food and significant weight loss. A puffy face can be more associated with different conditions, such as binge eating or fluid retention, rather than the extreme weight loss characteristic of anorexia. Frequent overeating is also not consistent with the behaviors exhibited by those suffering from this disorder, who usually severely restrict their food intake. Thus, amenorrhea stands out as a clear and specific symptom of anorexia nervosa.