Abstract
Anorexia nervosa (AN) is characterized by severe dietary restriction with effects that extend beyond body weight to gastrointestinal function, dietary tolerance and the gut microbiome. Weight restoration remains central to treatment, but studies suggest that microbial composition, microbial metabolites and gastrointestinal symptoms may not recover at the same pace as body mass. This narrative review examines gut microbiome alterations in AN through the clinical context of refeeding and dietetic care. Human and translational studies describe changes in microbial diversity, including shifts in carbohydrate fermenting taxa and their downstream metabolic products such as short-chain fatty acids (including butyrate), mucin-degrading taxa, neuroactive fecal metabolites, immune markers and microbial functional pathways. During refeeding, the substrates available to the gut microbiome are shaped by planned increases in energy intake, the extent to which planned meals are consumed, gastrointestinal tolerance, oral supplement use, constipation, laxative exposure or other medication, dietary variety and the gradual return of fermentable substrates. Current intervention evidence does not support routine use of probiotics, prebiotics or synbiotics for weight restoration, eating-disorder psychopathology or targeted microbiome modulation. Fiber-containing foods, fermented foods and dietary diversity may be relevant to dietary substrate exposure and gastrointestinal tolerance, but their use during AN rehabilitation should be framed as pragmatic dietetic care rather than as established microbiome-specific treatment. Their introduction should remain secondary to adequate energy provision, tolerance, normalization of eating patterns and avoidance of reinforcing restrictive behaviors. Dietitians can translate microbiome-related knowledge into cautious nutritional decision-making while ensuring that patient care remains centered on rehabilitation, safety and dietary adequacy.