The most likely diagnosis is bulimia nervosa. It is important to differentiate between types of eating disorders as the treatment varies depending on the diagnosis. Bulimia nervosa is characterized by frequent episodes (≥1 per week) of binge eating followed by inappropriate compensatory behaviors (self-induced vomiting or misuse of laxatives, diuretics, and enemas) due to fear of weight gain. Physical examination may reveal erosion of dental enamel, parotid gland swelling, xerosis, and Russell sign (scarring or calluses on the dorsum of the hand if used to induce vomiting). This patient meets diagnostic criteria for bulimia nervosa because she has recurrent episodes of binge eating with recurrent purging to try to compensate for the intake of calories.

Anorexia nervosa is characterized by persistent caloric intake restriction leading to significantly low body weight, a distorted body image, and an intense fear of gaining weight or becoming fat. Subtypes include restricting type (no binge eating or purging behaviors) and binge eating/purging type (purging with or without binging). The differentiating factor between bulimia nervosa and the purging subtype of anorexia nervosa is BMI. Because both purging and laxative abuse are ineffective in removing calories (although they may cause loss of water weight), patients with bulimia nervosa tend to be normal weight to slightly overweight, as seen in this patient. Conversely, the diagnostic criteria for anorexia require that the patient be underweight, generally with a BMI less than 18.5. Menstrual irregularities occur in both anorexia nervosa and bulimia nervosa and are present in approximately one half to one third of patients with bulimia. Although amenorrhea previously was a requirement for the diagnosis of anorexia nervosa, it has been removed from the diagnostic criteria in the DSM-5. Many experts consider anorexia nervosa and bulimia nervosa as a continuum, as one condition often develops from the other.

Binge eating disorder is defined as episodes of eating significantly more food in a short period than most people at least once per week over 3 months, while feeling a lack of control, and is often accompanied by feelings of disgust or guilt afterward but without attempted compensatory behaviors for excessive caloric intake.