Elena and Sofia are monozygotic twins who were raised together. At age 16, Elena was diagnosed with anorexia nervosa after displaying a severe restriction of food intake and an intense fear of gaining weight. Sofia, despite sharing the same home environment, has not developed the disorder, though she exhibits high levels of perfectionism and anxiety. Their father, a biologist, claims that Elena’s illness is entirely determined by her genetic makeup and altered brain chemistry, and that Sofia's traits prove this.