Providing effective nutritional rehabilitation to patients hospitalised with anorexia nervosa (AN) is challenging, partly due to conservative recommendations that advocate feeding patients at low energy intakes. An 'underfeeding syndrome' can develop when patients are not provided with adequate nutrition during treatment, whereby malnourished patients fail to restore weight in a timely matter, and even lose weight. Of particular concern, the reintroduction of carbohydrate in a starved patient can increase the risk of developing electrolyte, metabolic and organ dysfunction. The proposed trial assesses the efficacy and safety of a lower carbohydrate enteral formula (28% carbohydrate) against a standard enteral formula (54% carbohydrate), in adolescent and young adult patients (aged 15-25 years), hospitalised with AN.