Anorexia nervosa (AN), a psychiatric disorder characterized by extreme weight dysregulation commonly presents with comorbid anxiety. Therapeutic renourishment in AN is based primarily on clinical opinion and guidelines, with a weak evidence base. Compelling data implicate the intestinal microbiota in the regulation of adiposity and behavior, providing a strong rationale for exploring the role of this complex microbial community in the emergence and maintenance of, and recovery from AN. The overarching goal is to understand the precise mechanism(s) by which intestinal bacteria contribute to dysregulation of adiposity, BMI, anxiety, and stress in patients with AN. The investigators hypothesize that intestinal microbiotas that arise from prolonged starvation contribute to increases in adiposity upon refeeding and to persistently elevated anxiety and stress in individuals with AN. To test the hypothesis the investigators propose 3 specific aims. In aim 1, the investigators will identify the enteric bacterial groups associated with adiposity, BMI, anxiety, and stress in AN patients. The investigators will characterize the intestinal microbiota in acutely low weight AN patients (T1), in the same patients following weight restoration (T2), and in healthy controls (HC) via high throughput sequencing of the 16S rRNA gene.