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 Satiety ( ) is a state or condition of fullness gratified beyond the point of satisfaction, the opposite of hunger. It is a state which induces meal termination.Hetherington, M.Sensory-specific satiety and its importance in meal termination ''Neur ...

. Appetite exists in all higher life-forms, and serves to regulate adequate energy intake to maintain

metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

needs. It is regulated by a close interplay between the digestive tract, adipose tissue and the

brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...

. Appetite has a relationship with every individual's behavior. Appetitive behaviour also known as

approach behaviour The reward system (the mesocorticolimbic circuit) is a group of neural structures responsible for incentive salience (i.e., "wanting"; desire or craving for a reward and motivation), associative learning (primarily positive reinforcement and cla ...

, and

consummatory behaviour The reward system (the mesocorticolimbic circuit) is a group of neural structures responsible for incentive salience (i.e., "wanting"; desire or craving for a reward and motivation), associative learning (primarily positive reinforcement and cla ...

, are the only processes that involve energy intake, whereas all other behaviours affect the release of energy. When stressed, appetite levels may increase and result in an increase of food intake. Decreased desire to eat is termed anorexia, while

polyphagia Polyphagia or hyperphagia is an abnormally strong, incessant sensation of hunger or desire to eat often leading to overeating. In contrast to an increase in appetite following exercise, polyphagia does not subside after eating and often leads t ...

(or "hyperphagia") is increased eating. Dysregulation of appetite contributes to

anorexia nervosa Anorexia nervosa, often referred to simply as anorexia, is an eating disorder characterized by low weight, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. ''Anorexia'' is a term of Gre ...

bulimia nervosa Bulimia nervosa, also known as simply bulimia, is an eating disorder characterized by binge eating followed by purging or fasting, and excessive concern with body shape and weight. The aim of this activity is to expel the body of calories eaten ...

cachexia Cachexia () is a complex syndrome associated with an underlying illness, causing ongoing muscle loss that is not entirely reversed with nutritional supplementation. A range of diseases can cause cachexia, most commonly cancer, congestive heart fa ...

overeating Overeating occurs when an individual consumes more calories in relation to the energy that is expended via physical activity or expelled via excretion, leading to weight gain and often obesity. Overeating is the defining characteristic of bin ...

, and

binge eating disorder Binge eating disorder (BED) is an eating disorder characterized by frequent and recurrent binge eating episodes with associated negative psychological and social problems, but without the compensatory behaviors common to bulimia nervosa, OSFED, ...

Role in disease

A limited or excessive appetite is not necessarily pathological. Abnormal appetite could be defined as eating habits causing

malnutrition Malnutrition occurs when an organism gets too few or too many nutrients, resulting in health problems. Specifically, it is "a deficiency, excess, or imbalance of energy, protein and other nutrients" which adversely affects the body's tissues ...

and related conditions such as

obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's ...

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 numerous 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 The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...

and smell (" dysgeusia", bad taste) or the lack thereof may also effect appetite. Abnormal appetite may also be linked to genetics on a chromosomal scale, shown by the 1950s discovery of

Prader–Willi syndrome Prader–Willi syndrome (PWS) is a genetic disorder caused by a loss of function of specific genes on chromosome 15. In newborns, symptoms include weak muscles, poor feeding, and slow development. Beginning in childhood, those affected become ...

, 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

, and

. 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 Ghrelin (; or lenomorelin, INN) is a hormone produced by enteroendocrine cells of the gastrointestinal tract, especially the stomach, and is often called a "hunger hormone" because it increases the drive to eat. Blood levels of ghrelin are hi ...

, 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

may promote development of

. It has been found that ghrelin-reactive

IgG Immunoglobulin G (Ig G) is a type of antibody. Representing approximately 75% of serum antibodies in humans, IgG is the most common type of antibody found in blood circulation. IgG molecules are created and released by plasma B cells. Each IgG an ...

immunoglobulins affect ghrelin's

orexigenic An orexigenic, or appetite stimulant, is a drug, hormone, or compound that increases appetite and may induce hyperphagia. This can be a medication or a naturally occurring neuropeptide hormone, such as ghrelin, orexin or neuropeptide Y, which i ...

response. Other than genetically-stimulated appetite abnormalities, there are physiological ones that do not require genes for activation. For example,

and

leptin Leptin (from Greek λεπτός ''leptos'', "thin" or "light" or "small") is a hormone predominantly made by adipose cells and enterocytes in the small intestine that helps to regulate energy balance by inhibiting hunger, which in turn dimi ...

are released from the stomach and

adipose cells Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. Adipocytes are derived from mesenchymal stem cells which give rise to adipocytes through adipogenesis. I ...

, 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 resitant hypothalamus and eventually almost no leptin effect. From then all ghrelin production causes insatiable appetite.

Pediatric eating problems

Eating issues such as "

picky eating Avoidant/restrictive food intake disorder (ARFID) is a type of eating disorder in which people eat only within an extremely narrow repertoire of foods. It is a serious mental health condition that causes the individual to restrict food intake by ...

" 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 The glycemic (glycaemic) index (GI; ) is a number from 0 to 100 assigned to a food, with pure glucose arbitrarily given the value of 100, which represents the relative rise in the blood glucose level two hours after consuming that food. The GI of ...

has been thought to effect

; however, a study investigating the effect of satiety found that a high-glycemic food, potatoes, reduced appetite more than a low glycemic index food.

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 anorectics (appetite suppressants) were

fenfluramine Fenfluramine, sold under the brand name Fintepla, is a serotonergic medication used for the treatment of seizures associated with Dravet syndrome and Lennox–Gastaut syndrome.https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/212102s003l ...

and phentermine. A more recent addition is sibutramine which increases

serotonin Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and va ...

and noradrenaline levels in the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...

, 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 PYY 3-36 suggest that this agent may contribute to

weight loss Weight loss, in the context of medicine, health, or physical fitness, refers to a reduction of the total body mass, by a mean loss of fluid, body fat ( adipose tissue), or lean mass (namely bone mineral deposits, muscle, tendon, and other co ...

by suppressing appetite. Given the epidemic proportions of

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 ("

") is an effect of some diseases, and a side effect of some

prescription drug A prescription drug (also prescription medication or prescription medicine) is a pharmaceutical drug that legally requires a medical prescription to be dispensed. In contrast, over-the-counter drugs can be obtained without a prescription. The r ...

s. Stimulants such as

methylphenidate Methylphenidate, sold under the brand names Ritalin and Concerta among others, is the most widely prescribed central nervous system (CNS) stimulant medication used to treat attention deficit hyperactivity disorder (ADHD) and, to a lesser extent ...

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 Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the majo ...

available as an oral tablet, oxandrolone - an oral

anabolic steroid Anabolic steroids, also known more properly as anabolic–androgenic steroids (AAS), are steroidal androgens that include natural androgens like testosterone as well as synthetic androgens that are structurally related and have similar effects ...

, and dronabinol - a cannabinoid available in an oral capsule.

Ghrelin Ghrelin (; or lenomorelin, INN) is a hormone produced by enteroendocrine cells of the gastrointestinal tract, especially the stomach, and is often called a "hunger hormone" because it increases the drive to eat. Blood levels of ghrelin are hi ...

, a gut hormone recognized as affecting appetite, is under investigation. Ghrelin itself must be delivered

parenterally A route of administration in pharmacology and toxicology is the way by which a drug, fluid, poison, or other substance is taken into the body. Routes of administration are generally classified by the location at which the substance is applied. ...

and research has therefore focused on substances that can be taken orally. Rikkunshito, a traditional Japanese Kampo medicine, is under preliminary research for its potential to stimulate ghrelin and appetite.

References

{{Authority control Endocrinology Eating behaviors

Role in disease

Eating disorders

Obesity

Pediatric eating problems

Pharmacology and treatment

Suppression

Stimulation

See also

References