What condition is characterized by restriction of intake and a fear of gaining weight, with a BMI under 17?

The condition characterized by restriction of intake and a fear of gaining weight, with a BMI under 17, is anorexia nervosa. Anorexia is defined by a significantly low body weight relative to age, sex, developmental trajectory, and physical health, often resulting from extreme dietary restriction and an intense fear of gaining weight or becoming fat, even when underweight.

Individuals with anorexia may have a distorted body image, viewing themselves as overweight despite being underweight. The low BMI indicates severe undernourishment, which has serious health implications. This condition is distinct from bulimia, which involves cycles of binge eating followed by compensatory behaviors, and from compulsive overeating, where there may not be weight concerns but an inability to control eating. Body dysmorphic disorder primarily involves an obsessive focus on perceived flaws in physical appearance, which does not necessarily correlate with the restrictive eating patterns seen in anorexia.

Thus, the defining features of anorexia, including the fear of weight gain and the actual low body weight, clearly identify it as the correct answer.