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© The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. The Creative Commons Public Domain Dedication waiver (http:// creat iveco mmons. org/ publi cdoma in/ zero/1. 0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Restrictive eating disorders such as anorexia nervosa and atypical anorexia nervosa typically result in development of protein energy malnutrition. In severe protein energy malnutrition, alterations occur in all organ function, metabolism, and endocrine systems. Electrolyte levels must be closely monitored, particularly after initiating refeeding to avoid the refeeding syndrome, a rare but potentially deadly complication of refeeding the malnourished patient [1–5]. Anorexia nervosa is estimated to have the highest mortality of any psychological illness [6]. Approximately half of the mortality of anorexia nervosa occurs around the time of diagnosis, and those with severe malnutrition are most vulnerable. Weight and BMI are the most commonly used terms to categorise the severity of malnutrition. In recent years, our understanding of severe malnutrition has evolved with the recognition that individuals with eating disorders can demonstrate the physical and psychological effects of malnutrition even at normal or above normal weights. A new diagnostic category in DSM-5 “Atypical Anorexia Nervosa” describes those individuals who have lost a significant amount of weight but whose weight is in the normal or above normal range [7]. Weight suppression, the difference between highest weight and current weight, is a predictor of medical outcome in patients with restrictive eating disorders [8, 9]. In adults, a BMI < 15 kg/ m2 is recognised as conferring severe malnutrition. In adolescents, a BMI < 70% median BMI (corresponding approximately to a BMI < 5th percentile) indicates severe malnutrition. The Society for Adolescent Health and Medicine (SAHM) has expanded the definition of severe malnutrition in adolescents and young adults to include not only a low BMI, but also includes those who have lost > 20% of body mass over a period of one year or > 10% body mass over six months, in recognition of the effect of weight suppression on severity of medical complications [10]. This special edition of the journal addresses a number of important issues in the medical management of the malnourished patient with an eating disorder. Herein investigators provide data that challenge the existing consensus-based guidelines for refeeding. Gibson et al. describe the medical findings of 281 severely malnourished adult patients with extreme anorexia nervosa (BMI < 15 kg/m2, < 65% IBW) hospitalized on their medical stabilization unit [11]. On admission, 56% had bradycardia, 45% elevated liver function tests, 64% leukopenia and 20% thrombocytopenia. With refeeding, 38% developed hypoglycemia, 35% developed hypophosphatemia, and 33% developed edema. Almost 90% of the patients had low bone mineral density. Markedly elevated liver function tests predicted hypoglycemia and low BMI predicted refeeding hypophosphatemia. In an echocardiographic study of 124 severely malnourished adult patients with anorexia nervosa, Hanachi et al. [12] found that subclinical myocardial impairment was common. In their study, 27% of participants had pericardial effusions and 15% had evidence of left ventricular systolic dysfunction, which was associated with elevated transaminases and a diagnosis of anorexia nervosa – binge eating purging type. Taken together, these two studies demonstrate the high rates of medical complications in severe anorexia nervosa. Open Access