The need for novel approaches to understanding and treating anorexia nervosa (AN) is well recognized. The aim of this paper is to describe an integrative bio-psycho-social theory of maintaining factors in AN. We took a triangulation approach to develop a clinically relevant theory with face validity and internal consistency. We developed theoretical ideas from our clinical practice and reviewed theoretical ideas within the eating disorders and wider bio-psycho-social literature. The synthesis of these ideas and concepts into a clinically meaningful framework is described here. We suggest eight key factors central to understanding the maintenance and treatment resistance of anorexia nervosa: genetic or experiential predisposing factors; dysfunctional feelings processing and regulation systems; excessive vulnerable feelings; feared self' beliefs; starvation as a maladaptive physiological feelings regulation mechanism; maladaptive psychological coping modes; maladaptive social behaviour; and unmet physical and psychological core needs. Each of these factors serves to maintain the disorder. The concept of universal physical and psychological core needs can provide an underpinning integrative framework for working with this distinctly physical and psychological disorder. This framework could be used within any treatment model. We suggest that treatments which help address the profound lack of trust, emotional security and self-acceptance in this patient group will in turn address unmet needs and improve well-being. Copyright (c) 2016 John Wiley & Sons, Ltd.