Hunger and Satiety in Anorexia Nervosa

Appetite refers to the desire associated with eating. Both internal and external factors can stimulate appetite. Hunger and satiety are included in appetite regulation. Hunger is related to physiological needs and the commencement of eating. Satiety refers to a state without the urge to eat, where both the onset of satiety and post ingestion satiety are included.

Anorexia is abnormal loss of appetite for food. Anorexia nervosa is an eating disorder characterized by food restriction, despite low weight, leading to speculation about the presence of appetite alterations by weight loss.

AN is a syndrome of unknown etiology which has been well described since 1873, and which occurs most frequently in adolescent women. The syndrome is characterized by distorted body image, and fear of obesity, why low ideal weight is pursued. The disorder occurs in different degrees of severity with secondary endocrine and metabolic changes and disturbances. The symptoms may also include excessive physical activity, abuse of laxatives, or diuretics and self-induced vomiting.

There are multiple medical complications due to the starvation and weight loss in AN, several of which directly may affect appetite, for instance, delayed emptying of the stomach and constipation. Furthermore, compression of duodenum has been observed causing nausea and early satiety.

Hypothalamic hypogonadism is one of the well-known adaptive endocrine alterations in AN due to starvation and exaggerated exercise. Progesterone and testosterone is believed to stimulate appetite and eating, in a manner mediated centrally, selectively increasing the number of meals.

Moreover, AN patients have significantly higher levels of ghrelin, growth hormone (GH) and cortisol and significantly lower leptin, compared with partially recovered AN patients and constitutionally thin subjects.

Hunger and satiety are subjective sensations which may be influenced by sensory factors and palatability, including taste, smell and texture. A recent study suggested that patients with AN may have an altered perception of olfactory, gustatory stimuli, and reduced perception of bitter stimuli.

Other physiological factors such as, hypothalamic and mesolimbic endocannabinoids, enhance appetite by stimulating neurochemical pathways underlying both homeostatic and rewarding aspects of food intake. Endocannabinoids are involved in food-related reward mechanisms, and there are increasing evidence that these mechanisms are dysregulated in AN patients. Moreover, functional neuroimaging studies have demonstrated decreased food-related stimuli in brain areas of the mesolimbic reward system in AN patients.

Inclusion criteria

• Patients with severe AN admitted to the specialized nutrition unit at Center for Eating disorders at Odense University Hospital are included.

Exclusion criteria

• Patients admitted only for short-term water-electrolyte correction, are excluded.