[Anorexia nervosa: a model of malnutrition].
Anorexia nervosa is a typical kind of malnutrition resulting from chronic starvation. The malnutrition is related to a severe eating disorder (fear of eating and becoming fat) causing reduction of food intake. The large majority of the patients are women (95%). There are two types of anorexia nervosa with different prognosis and treatment: the restricting type and the "purging" type (with or without bulimia). In this kind of malnutrition, plasma nutritional markers are normal. The decrease in energy intake induces an adaptative decrease in energy expenditure. Body weight loss is related to a loss in fat free mass and in fat mass, although there is an increase in extracellular water. Below a body mass index of 15 kg/(m)(2), sodium and water retention require prescription of a low sodium diet. Several factors of resistance are operating in this disease, acting against body weight gain: metabolic wasting of energy expenditure (futile cycles), fear-related energy expenditure, dissimulations. Recovery is still long and difficult to obtain and requires a combined nutritional and psychotherapeutic approach.