Anorexia nervosa (AN) is a severe eating disorder which can lead to malnutrition and life threatening complications with high mortality rates. We designed our analysis to identify gut microbial taxa differentially abundant between AN and HC across different 16S rRNA gene datasets. We identified a reduced abundance, diversity and richness of Roseburia genus in the microbiota of patients with AN. Cares leading to partial recovery of patients with AN during hospitalization did not restore Roseburia to the levels of HC. AN dietary habit, either purgative or restrictive, did not affect Roseburia abundance. Roseburia genus and related species abundance were correlated with different health host metabolic markers. Roseburia species are key functional taxa in the human gut microbiome. Low gut Roseburia levels have been linked with other human pathologies. Our study highlights Roseburia species as a major decreased component in the gut of patients with AN.