Appetite is the desire to eat food items, usually due to hunger. Appealing foods can stimulate appetite even when hunger is absent, although appetite can be greatly reduced by satiety.
Role in disease
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.
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
Immunoglobulin G 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 Adipocyte, respectively, into the blood stream. Ghrelin stimulates feelings of hunger, whereas leptin stimulates feelings of satisfaction from food.[ ]
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
The
glycemic index is thought to affect satiety; however a study investigating the effect of satiety found that the glycemic index of foods did not predict effects on satiety and food intake.
Suppression
Mechanisms controlling appetite are a potential target for weight loss drugs. Appetite control mechanisms seem to strongly counteract undereating, whereas they appear weak to control overeating. Early
(appetite suppressants) were
fenfluramine and
phentermine. A more recent addition is
sibutramine which increases
serotonin and
noradrenaline levels in the central nervous system, but had to be withdrawn from the market when it was shown to have an adverse cardiovascular risk profile. Similarly, the appetite suppressant
rimonabant (a cannabinoid receptor antagonist) had to be withdrawn when it was linked with worsening depression and increased risk of suicide. Recent reports on
Recombinant DNA PYY 3-36 suggest that this agent may contribute to
weight loss by suppressing appetite.
Given the epidemic proportions of obesity in the Western world and the fact that it is increasing rapidly in some poorer countries, observers expect developments in this area to snowball in the near future.
Stimulation
Weight loss or loss of appetite ("
cachexia") is an effect of some diseases, and a side effect of some prescription drugs. Stimulants such as
methylphenidate commonly reduce appetite in patients,
and have been prescribed off-label for weight loss.
Three agents are approved for appetite stimulation in the United States: megestrol acetate - a
progesterone available as an oral tablet,
oxandrolone - an oral
anabolic steroid, and
dronabinol - THC, the principal
cannabinoid in
marijuana, available in an oral capsule.
Ghrelin, a gut hormone recognized as affecting appetite, is under investigation.
See also
