A limited or excessive appetite is not necessarily pathological. Abnormal appetite could be defined as eating habits causing
malnutrition and related conditions such as
obesity and its related problems. Both genetic and environmental factors may regulate appetite, and abnormalities in either may lead to abnormal appetite. Poor appetite (
anorexia) can have a number of causes, but may be a result of physical (infectious, autoimmune or malignant disease) or psychological (stress, mental disorders) factors. Likewise,
hyperphagia (excessive eating) may be a result of hormonal imbalances, mental disorders (e.g.,
depression) and others.
Dyspepsia, also known as indigestion, can also affect appetite as one of its symptoms is feeling "overly full" soon after beginning a meal.
Taste and
smell ("
dysgeusia", bad taste) or the lack thereof may also affect appetite. Abnormal appetite may also be linked to genetics on a chromosomal scale, shown by the 1950s discovery of
Prader–Willi syndrome, a type of obesity caused by chromosome alterations. Additionally, anorexia nervosa and bulimia nervosa are more commonly found in females than males – thus hinting at a possibility of a linkage to the X-chromosome.
Eating disorders Dysregulation of appetite lies at the root of
anorexia nervosa,
bulimia nervosa, and
binge eating disorder. Anorexia nervosa is a mental disorder characterized as severe dietary restriction and intense fear of weight gain. Furthermore, persons with anorexia nervosa may exercise ritualistically. Individuals who have anorexia have high levels of
ghrelin, a hormone that stimulates appetite, so the body is trying to cause hunger, but the urge to eat is being suppressed by the person. Binge eating disorder (commonly referred to as BED) is described as eating excessively (or uncontrollably) between periodic time intervals. The risk for BED can be present in children and most commonly manifests during adulthood. Studies suggest that the heritability of BED in adults is approximately 50%. Similarly to bulimia, some people may be involved in purging and binging. They might vomit after food intake or take purgatives.
Body dysmorphic disorder may involve food restriction in an attempt to deal with a perceived fault, and may be associated with depression and social isolation.
Obesity Various hereditary forms of obesity have been traced to defects in hypothalamic signaling (such as the leptin receptor and the
MC-4 receptor) or are still awaiting characterization –
Prader-Willi syndrome – in addition, decreased response to
satiety may promote development of
obesity. It has been found that ghrelin-reactive
IgG immunoglobulins affect ghrelin's
orexigenic response. Other than genetically stimulated appetite abnormalities, there are physiological ones that do not require genes for activation. For example,
ghrelin and
leptin are released from the stomach and
adipose cells, respectively, into the blood stream. Ghrelin stimulates feelings of hunger, whereas leptin stimulates feelings of satisfaction from food. Any changes in normal production levels of these two hormones can lead to obesity. The amount of leptin hormone production is stimulated by body fat percentage. When body fat accumulates there is overproduction of leptin causing a resistant hypothalamus and eventually almost no leptin effect. From then all ghrelin production causes insatiable appetite.
Pediatric eating problems Eating issues such as "
picky eating" affects about 25% of children, but among children with
development disorders this number may be significantly higher, which in some cases may be related to the sounds, smells, and tastes (
sensory processing disorder). ==Pharmacology and treatment==