The investigators will compare the abundances of specific enteric taxa with adiposity, BMI and behavior (anxiety and stress) in this study population. In aim 2, The investigators will characterize the functional impact of the intestinal microbiota of AN patients on adiposity and BMI when transplanted into germ free (GF) mice. The investigators will transplant uncultured microbiotas from AN patients (at T1 and T2) and HC into GF mice and assess the impact of enteric microbes on adiposity. In aim 3, the investigators will characterize the functional impact of the intestinal microbiota of AN patients on anxiety and stress, and molecular biomarkers of these behaviors, when transplanted into GF mice. The investigators will transplant uncultured microbiotas from T1 AN patients and HC into GF mice and assess the impact of enteric microbes on anxiety and stress. GF mice gavaged with sterile phosphate buffer saline will be used as controls in aims 2 and 3. The proposed science is significant in pioneering the combination of large scale 16S rRNA gene sequencing-based studies of intestinal microbiotas in AN with exploration of their functional influence on adiposity and behavioral traits associated with AN. The results will provide direction on how best to test adjunct interventions for AN with pre-, pro-, anti-, or syn-biotics to enhance current approaches to therapeutic weight restoration and improve treatment outcome. The science is highly innovative as it will investigate an entirely novel factor in AN, the intestinal microbiota, and use a novel approach to identify enteric microbes that impact adiposity and behavior in this devastating illness. Additionally, the investigators will hope to study an entirely novel factor (namely, the intestinal microbiota) as a contributor to the underlying pathophysiology of AN.