Appetite
Encyclopedia
The appetite is the desire to eat
food
, felt as hunger
. Appetite exists in all higher life-forms, and serves to regulate adequate energy intake to maintain metabolic
needs. It is regulated by a close interplay between the digestive tract, adipose tissue
and the brain
. Decreased desire to eat is termed anorexia
, while polyphagia
(or "hyperphagia") is increased eating. Dysregulation of appetite contributes to anorexia nervosa
, bulimia nervosa
, cachexia
, overeating
, and binge eating disorder
.
, a hormone that appeared to provide negative feedback. Later studies showed that appetite regulation is an immensely complex process involving the gastrointestinal tract
, many hormone
s, and both the central
and autonomic nervous system
s.
, a part of the brain, is the main regulatory organ for the human appetite. The neuron
s that regulate appetite appear to be mainly serotonergic
, although neuropeptide Y
(NPY) and Agouti-related peptide
(AGRP) also play a vital role. Hypothalamocortical and hypothalamolimbic projections contribute to the awareness of hunger, and the somatic processes controlled by the hypothalamus include vagal
tone (the activity of the parasympathetic
autonomic nervous system
), stimulation of the thyroid
(thyroxine
regulates the metabolic rate), the hypothalamic-pituitary-adrenal axis
and a large number of other mechanisms. Opioid receptor
-related processes in the nucleus accumbens
and ventral pallidum effect the palatability
of foods.
, ghrelin
, PYY 3-36, orexin
and cholecystokinin
; all modify the hypothalamic response. They are produced by the digestive tract and by adipose tissue
(leptin). Systemic mediators, such as tumor necrosis factor-alpha (TNFα), interleukin
s 1 and 6 and corticotropin-releasing hormone
(CRH) influence appetite negatively; this mechanism explains why ill people often eat less.
In addition, the biological clock (which is regulated by the hypothalamus) modifies hunger. Processes from other cerebral loci, such as from the limbic system
and the cerebral cortex
, project on the hypothalamus and modify appetite. This explains why in clinical depression
and stress
, energy intake can change quite drastically.
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
) may 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.
Dysregulation of appetite lies at the root of anorexia nervosa
, bulimia nervosa
and binge eating disorder
. In addition, decreased response to satiety may promote development of obesity
.
Various hereditary forms of obesity have been traced to defects in hypothalamic signalling (such as the leptin receptor and the MC-4
receptor), or are still awaiting characterisation (Prader-Willi syndrome
).
s 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
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 even increasing rapidly in some poorer countries, observers expect developments in this area to snowball in the near future. Dieting alone is ineffective in most obese adults - and even obese adults who successfully lose weight through dieting, often put weight back on afterwards.
Appetite-enhancing drugs are medications given to prevent drastic weight loss in the in patients suffering from diseases as AIDS . In reality, the term used to describe these drugs are orexigenic. Over the years there has been many controversy over these drugs and many people have decided to use an organic alternative to these drugs which is fish oil. Some examples of these drugs include:
• Remeron
• Periactinan
• Marinol
• Megace
In comparison to fathers, mothers play a more predominant role in encouraging a child to consume food. Based on the expectation males should eat more than females, a mother's approach to praise girls for consuming food is more effective than a father's method of pressuring boys. Overall parental influence can enhance a child's appetite and studies have demonstrated that a third of children are more likely to eat if in the presence of a parent compared to dining alone.Page text.[3]
Eating
Eating is the ingestion of food to provide for all organisms their nutritional needs, particularly for energy and growth. Animals and other heterotrophs must eat in order to survive: carnivores eat other animals, herbivores eat plants, omnivores consume a mixture of both plant and animal matter,...
food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
, felt as hunger
Hunger
Hunger is the most commonly used term to describe the social condition of people who frequently experience the physical sensation of desiring food.-Malnutrition, famine, starvation:...
. Appetite exists in all higher life-forms, and serves to regulate adequate energy intake to maintain metabolic
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
needs. It is regulated by a close interplay between the digestive tract, adipose tissue
Adipose tissue
In histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...
and the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
. Decreased desire to eat is termed anorexia
Anorexia (symptom)
Anorexia is the decreased sensation of appetite...
, while polyphagia
Polyphagia
Polyphagia means "eating too much". It derives from the Greek words πολύς which means "very much", and φαγῶ , verb for "I eat"....
(or "hyperphagia") is increased eating. Dysregulation of appetite contributes to anorexia nervosa
Anorexia nervosa
Anorexia nervosa is an eating disorder characterized by refusal to maintain a healthy body weight and an obsessive fear of gaining weight. Although commonly called "anorexia", that term on its own denotes any symptomatic loss of appetite and is not strictly accurate...
, bulimia nervosa
Bulimia nervosa
Bulimia nervosa is an eating disorder characterized by binge eating and purging or consuming a large amount of food in a short amount of time, followed by an attempt to rid oneself of the food consumed, usually by purging and/or by laxative, diuretics or excessive exercise. Bulimia nervosa is...
, cachexia
Cachexia
Cachexia or wasting syndrome is loss of weight, muscle atrophy, fatigue, weakness, and significant loss of appetite in someone who is not actively trying to lose weight...
, overeating
Overeating
Overeating generally refers to the long-term consumption of excess food in relation to the energy that an organism expends , leading to weight gainingand often obesity. It may be regarded as an eating disorder....
, and binge eating disorder
Binge eating disorder
Binge eating disorder is the most common eating disorder in the United States affecting 3.5% of females and 2% of males and is prevalent in up to 30% of those seeking weight loss treatment...
.
Regulation
The regulation of appetite (the appestat) has been the subject of much research in the . Breakthroughs included the discovery, in 1994, of leptinLeptin
Leptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones...
, a hormone that appeared to provide negative feedback. Later studies showed that appetite regulation is an immensely complex process involving the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
, many hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s, and both the central
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
and autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
s.
Effector
The hypothalamusHypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
, a part of the brain, is the main regulatory organ for the human appetite. The neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s that regulate appetite appear to be mainly serotonergic
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
, although neuropeptide Y
Neuropeptide Y
Neuropeptide Y is a 36-amino acid peptide neurotransmitter found in the brain and autonomic nervous system."NPY has been associated with a number of physiologic processes in the brain, including the regulation of energy balance, memory and learning, and epilepsy." The main effect is increased food...
(NPY) and Agouti-related peptide
Agouti-related peptide
Agouti-related protein also called Agouti-related peptide is a neuropeptide produced in the brain by the AgRP/NPY neuron. It is only synthesised in NPY containing cell bodies located in the ventromedial part of the arcuate nucleus in the hypothalamus...
(AGRP) also play a vital role. Hypothalamocortical and hypothalamolimbic projections contribute to the awareness of hunger, and the somatic processes controlled by the hypothalamus include vagal
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
tone (the activity of the parasympathetic
Parasympathetic nervous system
The parasympathetic nervous system is one of the two main divisions of the autonomic nervous system . The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously...
autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
), stimulation of the thyroid
Thyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...
(thyroxine
Thyroxine
Thyroxine, or 3,5,3',5'-tetraiodothyronine , a form of thyroid hormones, is the major hormone secreted by the follicular cells of the thyroid gland.-Synthesis and regulation:...
regulates the metabolic rate), the hypothalamic-pituitary-adrenal axis
Hypothalamic-pituitary-adrenal axis
The hypothalamic-pituitary-adrenal axis , also known as thelimbic-hypothalamic-pituitary-adrenal axis and, occasionally, as the hypothalamic-pituitary-adrenal-gonadotropic axis, is a complex set of direct influences and feedback interactions among the hypothalamus, the pituitary gland ,...
and a large number of other mechanisms. Opioid receptor
Opioid receptor
Opioid receptors are a group of G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin. The opioid receptors are ~40% identical to somatostatin receptors...
-related processes in the nucleus accumbens
Nucleus accumbens
The nucleus accumbens , also known as the accumbens nucleus or as the nucleus accumbens septi , is a collection of neurons and forms the main part of the ventral striatum...
and ventral pallidum effect the palatability
Palatability
Palatability is the hedonic reward provided by foods or fluids that are agreeable to the "palate" in regard to the homeostatic satisfaction of nutritional, water, or energy needs. The palatability of a food or fluid, unlike its flavor or taste, varies with the state of an individual: it is lower...
of foods.
Sensor
The hypothalamus senses external stimuli mainly through a number of hormones such as leptinLeptin
Leptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones...
, ghrelin
Ghrelin
Ghrelin is a 28 amino acid peptide and hormone that is produced mainly by P/D1 cells lining the fundus of the human stomach and epsilon cells of the pancreas that stimulates hunger. Ghrelin levels increase before meals and decrease after meals. It is considered the counterpart of the hormone...
, PYY 3-36, orexin
Orexin
Orexins, also called hypocretins, are the common names given to a pair of excitatory neuropeptide hormones that were simultaneously discovered by two groups of researchers in rat brains....
and cholecystokinin
Cholecystokinin
Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein...
; all modify the hypothalamic response. They are produced by the digestive tract and by adipose tissue
Adipose tissue
In histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...
(leptin). Systemic mediators, such as tumor necrosis factor-alpha (TNFα), interleukin
Interleukin
Interleukins are a group of cytokines that were first seen to be expressed by white blood cells . The term interleukin derives from "as a means of communication", and "deriving from the fact that many of these proteins are produced by leukocytes and act on leukocytes"...
s 1 and 6 and corticotropin-releasing hormone
Corticotropin-releasing hormone
Corticotropin-releasing hormone , originally named corticotropin-releasing factor , and also called corticoliberin, is a polypeptide hormone and neurotransmitter involved in the stress response...
(CRH) influence appetite negatively; this mechanism explains why ill people often eat less.
In addition, the biological clock (which is regulated by the hypothalamus) modifies hunger. Processes from other cerebral loci, such as from the limbic system
Limbic system
The limbic system is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, septum, limbic cortex and fornix, which seemingly support a variety of functions including emotion, behavior, long term memory, and olfaction. The term "limbic" comes from the Latin...
and the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
, project on the hypothalamus and modify appetite. This explains why in clinical depression
Clinical depression
Major depressive disorder is a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem, and by loss of interest or pleasure in normally enjoyable activities...
and stress
Stress (medicine)
Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...
, energy intake can change quite drastically.
Role in disease
A limited or excessive appetite is not necessarily pathological. Abnormal appetite could be defined as eating habits causing malnutritionMalnutrition
Malnutrition is the condition that results from taking an unbalanced diet in which certain nutrients are lacking, in excess , or in the wrong proportions....
and related conditions such as obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
and its related problems.
Both genetic and environmental factors may regulate appetite, and abnormalities in either may lead to abnormal appetite. Poor appetite (anorexia
Anorexia (symptom)
Anorexia is the decreased sensation of appetite...
) may 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
Clinical depression
Major depressive disorder is a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem, and by loss of interest or pleasure in normally enjoyable activities...
) and others.
Dysregulation of appetite lies at the root of anorexia nervosa
Anorexia nervosa
Anorexia nervosa is an eating disorder characterized by refusal to maintain a healthy body weight and an obsessive fear of gaining weight. Although commonly called "anorexia", that term on its own denotes any symptomatic loss of appetite and is not strictly accurate...
, bulimia nervosa
Bulimia nervosa
Bulimia nervosa is an eating disorder characterized by binge eating and purging or consuming a large amount of food in a short amount of time, followed by an attempt to rid oneself of the food consumed, usually by purging and/or by laxative, diuretics or excessive exercise. Bulimia nervosa is...
and binge eating disorder
Binge eating disorder
Binge eating disorder is the most common eating disorder in the United States affecting 3.5% of females and 2% of males and is prevalent in up to 30% of those seeking weight loss treatment...
. In addition, decreased response to satiety may promote development of obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
.
Various hereditary forms of obesity have been traced to defects in hypothalamic signalling (such as the leptin receptor and the MC-4
Melanocyte-stimulating hormone
The melanocyte-stimulating hormones are a class of peptide hormones that are produced by cells in the intermediate lobe of the pituitary gland...
receptor), or are still awaiting characterisation (Prader-Willi syndrome
Prader-Willi syndrome
Prader–Willi syndrome is a rare genetic disorder in which seven genes on chromosome 15 are deleted or unexpressed on the paternal chromosome...
).
Pharmacology
Mechanisms controlling appetite are a potential target for weight loss drugs. Early anorecticAnorectic
An anorectic or anorexic , also known as anorexigenic or appetite suppressant, is a dietary supplement and/or drug which reduces appetite, food consumption, and as a result, causes weight loss to occur.-List of anorectics:Numerous pharmaceutical compounds are marketed as appetite suppressants.The...
s were fenfluramine
Fenfluramine
Fenfluramine is a drug that was part of the Fen-Phen anti-obesity medication . Fenfluramine was introduced on the U.S. market in 1973. It is the racemic mixture of two enantiomers, dextrofenfluramine and levofenfluramine...
and phentermine
Phentermine
Phentermine, a contraction of "phenyl-tertiary-butylamine", is a psychostimulant drug of the phenethylamine class, chemically related to amphetamine. It is used medically as an appetite suppressant....
. A more recent addition is sibutramine
Sibutramine
Sibutramine is an oral anorexiant. Until 2010 it was marketed and prescribed as an adjunct in the treatment of exogenous obesity along with diet and exercise...
which increases serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
and noradrenaline levels in the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
, but had to be withdrawn from the market when it was shown to have an adverse cardiovascular risk profile. Similarly, the appetite suppressant rimonabant
Rimonabant
Rimonabant is an anorectic antiobesity drug that has been withdrawn from the market. It is an inverse agonist for the cannabinoid receptor CB1...
(a cannabinoid receptor antagonist) had to be withdrawn when it was linked with worsening depression and increased risk of suicide. Recent reports on recombinant
Recombinant DNA
Recombinant DNA molecules are DNA sequences that result from the use of laboratory methods to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms...
PYY 3-36 suggest that this agent may contribute to weight loss
Weight loss
Weight loss, in the context of medicine, health or physical fitness, is a reduction of the total body mass, due to a mean loss of fluid, body fat or adipose tissue and/or lean mass, namely bone mineral deposits, muscle, tendon and other connective tissue...
by suppressing appetite.
Given the epidemic proportions of obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
in the Western world, and the fact that it is even increasing rapidly in some poorer countries, observers expect developments in this area to snowball in the near future. Dieting alone is ineffective in most obese adults - and even obese adults who successfully lose weight through dieting, often put weight back on afterwards.
Appetite-enhancing drugs are medications given to prevent drastic weight loss in the in patients suffering from diseases as AIDS . In reality, the term used to describe these drugs are orexigenic. Over the years there has been many controversy over these drugs and many people have decided to use an organic alternative to these drugs which is fish oil. Some examples of these drugs include:
• Remeron
• Periactinan
• Marinol
• Megace
Children's appetite
Children’s appetite on fat content does not change. When children eat a certain amount of food daily they do not account for how much they are eating. The problem nowadays is children are eating food with more fat content which will lead to diseases such as obesity. To avoid such problem one factor that can help children avoid being over weighted is to reduce the amount of fats in their food. Even if the fat content of the food is reduced, children’s appetite towards the food would not differ. The child would not notice the differences if there is a decrease of fat in their foods therefore the child's liking towards the food would not be affected.In comparison to fathers, mothers play a more predominant role in encouraging a child to consume food. Based on the expectation males should eat more than females, a mother's approach to praise girls for consuming food is more effective than a father's method of pressuring boys. Overall parental influence can enhance a child's appetite and studies have demonstrated that a third of children are more likely to eat if in the presence of a parent compared to dining alone.Page text.[3]
See also
- Specific appetiteSpecific appetiteSpecific appetite, also known as specific hunger is a drive to eat foods with specific flavors or other characteristics.Regulation of homeostasis is essential to the survival of animals...
- OrexigenicOrexigenicAn orexigenic is a drug or hormone that increases appetite. This can be a naturally occurring neuropeptide hormone such as ghrelin, orexin or neuropeptide Y, or a medication which increases hunger and therefore enhances food consumption...