Amandines de Provence, poster by Leonetto Cappiello, 1900

Eating (also known as consuming) is the

ingestion Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms in ...

food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is in ...

, typically to provide a

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fu ...

with

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of ...

and to allow for

growth Growth may refer to: Biology * Auxology, the study of all aspects of human physical growth * Bacterial growth * Cell growth * Growth hormone, a peptide hormone that stimulates growth * Human development (biology) * Plant growth * Secondary grow ...

. Animals and other heterotrophs must eat in order to survive —

carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other s ...

s eat other animals,

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

s eat plants,

omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nu ...

s consume a mixture of both plant and animal matter, and detritivores eat

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts comm ...

. Fungi digest organic matter outside their bodies as opposed to animals that digest their food inside their bodies. For humans, eating is an activity of daily living. Some individuals may limit their amount of nutritional intake. This may be a result of a lifestyle choice, due to

hunger In politics, humanitarian aid, and the social sciences, hunger is defined as a condition in which a person does not have the physical or financial capability to eat sufficient food to meet basic Human nutrition, nutritional needs for a sustaine ...

famine A famine is a widespread scarcity of food, caused by several factors including war, natural disasters, crop failure, population imbalance, widespread poverty, an economic catastrophe or government policies. This phenomenon is usually accompan ...

, as part of a diet or as religious fasting.

Eating practices among humans

Many homes have a large kitchen area devoted to preparation of meals and food, and may have a

dining room A dining room is a room for consuming food. In modern times it is usually adjacent to the kitchen for convenience in serving, although in medieval times it was often on an entirely different floor level. Historically the dining room is furnis ...

, dining hall, or another designated area for eating. Most societies also have

restaurant A restaurant is a business that prepares and serves food and drinks to customers. Meals are generally served and eaten on the premises, but many restaurants also offer take-out and food delivery services. Restaurants vary greatly in appearan ...

food court A food court (in Asia-Pacific also called food hall or hawker centre) is generally an indoor plaza or common area within a facility that is contiguous with the counters of multiple food vendors and provides a common area for self-serve dinner. ...

s, and food vendors so that people may eat when away from home, when lacking time to prepare food, or as a social occasion.John Raulston Saul (1995), "The Doubter's Companion", 155 At their highest level of sophistication, these places become "theatrical spectacles of global cosmopolitanism and

myth Myth is a folklore genre consisting of narratives that play a fundamental role in a society, such as foundational tales or origin myths. Since "myth" is widely used to imply that a story is not objectively true, the identification of a narrat ...

."David Grazian (2008), "On the Make: The Hustle of Urban Nightlife", 32 At

picnic A picnic is a meal taken outdoors ( ''al fresco'') as part of an excursion, especially in scenic surroundings, such as a park, lakeside, or other place affording an interesting view, or else in conjunction with a public event such as preceding ...

s, potlucks, and food festivals, eating is in fact the primary purpose of a social gathering. At many social events, food and beverages are made available to attendees. People usually have two or three

meal A meal is an eating occasion that takes place at a certain time and includes consumption of food. The names used for specific meals in English vary, depending on the speaker's culture, the time of day, or the size of the meal. Although they c ...

s a day.

Snack A snack is a small portion of food generally eaten between meals. Snacks come in a variety of forms including packaged snack foods and other processed foods, as well as items made from fresh ingredients at home. Traditionally, snacks are ...

s of smaller amounts may be consumed between meals. Doctors in the UK recommend three meals a day (with between 400–600 kcal per meal), with four to six hours between. Having three well-balanced meals (described as: half of the plate with vegetables, 1/4 protein food as meat, ..and 1/4 carbohydrates as pasta, rice) will then amount to some 1800–2000 kcal, which is the average requirement for a regular person. In jurisdictions under

Sharia law Sharia (; ar, شريعة, sharīʿa ) is a body of religious law that forms a part of the Islamic tradition. It is derived from the religious precepts of Islam and is based on the sacred scriptures of Islam, particularly the Quran and the H ...

, it may be proscribed for

Muslim Muslims ( ar, المسلمون, , ) are people who adhere to Islam, a monotheistic religion belonging to the Abrahamic tradition. They consider the Quran, the foundational religious text of Islam, to be the verbatim word of the God of Abrah ...

adults during the daylight hours of

Ramadan , type = islam , longtype = Religious , image = Ramadan montage.jpg , caption=From top, left to right: A crescent moon over Sarıçam, Turkey, marking the beginning of the Islamic month of Ramadan. Ramadan Quran reading in Bandar Torkaman, Iran. ...

.Sharia and Social Engineering: p 143, R. Michael Feener - 2013FOOD & EATING IN MEDIEVAL EUROPE - Page 73, Joel T. Rosenthal - 1998Conscious Eating: Second Edition - Page 9, Gabriel Cousens, M.D. - 2009

Development in humans

Girl with chopsticks at dumpling restaurant

Newborn babies do not eat adult foods. They survive solely on breast milk or formula. Small amounts of pureed food are sometimes fed to young infants as young as two or three months old, but most infants do not eat adult food until they are between six and eight months old. Young babies eat pureed

baby food Baby food is any soft easily consumed food other than breastmilk or infant formula that is made specifically for human babies between four and six months and two years old. The food comes in many varieties and flavors that are purchased ready-ma ...

s because they have few teeth and immature digestive systems. Between 8 and 12 months of age, the digestive system improves, and many babies begin eating finger foods. Their diet is still limited, however, because most babies lack molars or canines at this age, and often have a limited number of incisors. By 18 months, babies often have enough teeth and a sufficiently mature digestive system to eat the same foods as adults. Learning to eat is a messy process for children, and children often do not master neatness or eating etiquette until they are five or six years old.

Eating positions

Eating positions vary according to the different regions of the world, as culture influences the way people eat their meals. For example, most of the Middle Eastern countries, eating while sitting on the floor is most common, and it is believed to be healthier than eating while sitting to a table. Eating in a reclining position was favored by the

Ancient Greeks Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...

at a celebration they called a

symposium In ancient Greece, the symposium ( grc-gre, συμπόσιον ''symposion'' or ''symposio'', from συμπίνειν ''sympinein'', "to drink together") was a part of a banquet that took place after the meal, when drinking for pleasure was acc ...

, and this custom was adopted by the

Ancient Romans In modern historiography, ancient Rome refers to Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom (753–50 ...

Ancient Hebrews The terms ''Hebrews'' (Hebrew: / , Modern: ' / ', Tiberian: ' / '; ISO 259-3: ' / ') and ''Hebrew people'' are mostly considered synonymous with the Semitic-speaking Israelites, especially in the pre-monarchic period when they were still ...

also adopted this posture for traditional celebrations of

Passover Passover, also called Pesach (; ), is a major Jewish holiday that celebrates the Biblical story of the Israelites escape from slavery in Egypt, which occurs on the 15th day of the Hebrew month of Nisan, the first month of Aviv, or spring. ...

Compulsive overeating

Compulsive overeating, or emotional eating, is "the tendency to eat in response to negative emotions". Empirical studies have indicated that anxiety leads to decreased food consumption in people with normal weight and increased food consumption in the obese. Many laboratory studies showed that overweight individuals are more emotionally reactive and are more likely to overeat when distressed than people of normal weight. Furthermore, it was consistently found that obese individuals experience negative emotions more frequently and more intensively than do normal weight persons. The naturalistic study by Lowe and Fisher compared the emotional reactivity and emotional eating of normal and overweight female college students. The study confirmed the tendency of obese individuals to overeat, but these findings applied only to snacks, not to meals. That means that obese individuals did not tend to eat more while having meals; rather, the amount of snacks they ate between meals was greater. One possible explanation that Lowe and Fisher suggest is obese individuals often eat their meals with others and do not eat more than average due to the reduction of distress because of the presence of other people. Another possible explanation would be that obese individuals do not eat more than the others while having meals due to social desirability. Conversely, snacks are usually eaten alone.

Hunger and satiety

There are many physiological mechanisms that control starting and stopping a meal. The control of food intake is a physiologically complex, motivated behavioral system. Hormones such as cholecystokinin, bombesin, neurotensin, anorectin,

calcitonin Calcitonin is a 32 amino acid peptide hormone secreted by parafollicular cells (also known as C cells) of the thyroid (or endostyle) in humans and other chordates. in the ultimopharyngeal body. It acts to reduce blood calcium (Ca2+), opposing the ...

enterostatin Enterostatin is a pentapeptide derived from a proenzyme in the gastrointestinal tract called procolipase. It reduces food intake, in particular fat intake, when given peripherally or into the brain. Function Enterostatin is created in the intes ...

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 ...

and corticotropin-releasing hormone have all been shown to suppress food intake.Geiselman, P.J. (1996). Control of food intake. A physiologically complex, motivated behavioral system. Endocrinol Metab Clin North Am. 1996 Dec;25(4):815-29.

Initiation

German Shepherd puppy eating out of a human hand

There are numerous signals given off that initiate

. There are environmental signals, signals from the gastrointestinal system, and metabolic signals that trigger hunger. The environmental signals come from the body's

senses A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of stimuli. (For example, in the human body, the brain which is part of the central nervous system re ...

. The feeling of hunger could be triggered by the smell and thought of food, the sight of a plate, or hearing someone talk about food. The signals from the stomach are initiated by the release of the peptide hormone ghrelin. Ghrelin is a hormone that increases appetite by signaling to the brain that a person is hungry. Environmental signals and ghrelin are not the only signals that initiate hunger, there are other metabolic signals as well. As time passes between meals, the body starts to take nutrients from long-term reservoirs. When the glucose levels of cells drop (glucoprivation), the body starts to produce the feeling of hunger. The body also stimulates eating by detecting a drop in cellular lipid levels (lipoprivation). Both the brain and the liver monitor the levels of metabolic fuels. The brain checks for glucoprivation on its side of the blood–brain barrier (since glucose is its fuel), while the liver monitors the rest of the body for both lipoprivation and glucoprivation.

Termination

There are short-term signals of satiety that arise from the head, the stomach, the intestines, and the liver. The long-term signals of satiety come from adipose tissue. The taste and odor of food can contribute to short-term satiety, allowing the body to learn when to stop eating. The stomach contains receptors to allow us to know when we are full. The intestines also contain receptors that send satiety signals to the brain. The hormone cholecystokinin is secreted by the

duodenum The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine m ...

, and it controls the rate at which the stomach is emptied. This hormone is thought to be a satiety signal to the brain. Peptide YY 3-36 is a hormone released by the

small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...

and it is also used as a satiety signal to the brain. Insulin also serves as a satiety signal to the brain. The brain detects

insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism ...

in the blood, which indicates that nutrients are being absorbed by cells and a person is getting full. Long-term satiety comes from the fat stored in adipose tissue. Adipose tissue secretes the hormone

, and leptin suppresses appetite. Long-term satiety signals from adipose tissue regulates short-term satiety signals.

Role of the brain

The brain stem can control food intake, because it contains neural circuits that detect hunger and satiety signals from other parts of the body. The brain stem's involvement of food intake has been researched using rats. Rats that have had the motor neurons in the brain stem disconnected from the neural circuits of the cerebral hemispheres (decerebration), are unable to approach and eat food. Instead they have to obtain their food in a liquid form. This research shows that the brain stem does in fact play a role in eating. There are two peptides in the

hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus ...

that produce hunger, melanin concentrating hormone (MCH) and orexin. MCH plays a bigger role in producing hunger. In mice, MCH stimulates feeding and a mutation causing the overproduction of MCH led to overeating and obesity. Orexin plays a greater role in controlling the relationship between eating and sleeping. Other peptides in the hypothalamus that induce eating are neuropeptide Y (NPY) and agouti-related protein (AGRP). Satiety in the hypothalamus is stimulated by leptin. Leptin targets the receptors on the arcuate nucleus and suppresses the secretion of MCH and orexin. The arcuate nucleus also contains two more peptides that suppress hunger. The first one is

cocaine- and amphetamine-regulated transcript Cocaine- and amphetamine-regulated transcript, also known as CART, is a neuropeptide protein that in humans is encoded by the ''CARTPT'' gene. CART appears to have roles in reward, feeding, and stress, and it has the functional properties of an ...

(CART), the second is α-MSH (α-melanocyte-stimulating hormone).

Disorders

Physiologically, eating is generally triggered by

, but there are numerous physical and psychological conditions that can affect

appetite 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. Appetite exists in all higher life-forms, and serves to regu ...

and disrupt normal eating patterns. These include depression, food allergies, ingestion of certain chemicals, bulimia,

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 ...

pituitary gland In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The h ...

malfunction and other

endocrine The endocrine system is a messenger system comprising feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs. In vertebrates, the hypothalamus is the neur ...

problems, and numerous other illnesses and

eating disorder An eating disorder is a mental disorder defined by abnormal eating behaviors that negatively affect a person's physical or mental health. Only one eating disorder can be diagnosed at a given time. Types of eating disorders include binge eating d ...

s. A chronic lack of nutritious food can cause various illnesses, and will eventually lead to

starvation Starvation is a severe deficiency in caloric energy intake, below the level needed to maintain an organism's life. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, de ...

. When this happens in a locality on a massive scale, it is considered a

. If eating and drinking is not possible, as is often the case when recovering from

surgery Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pa ...

, alternatives are enteral nutrition and parenteral nutrition.Heisler, Jennifer. "Surgery." About.com. N.p., May–June 2010. Web. 13 Mar. 2013.

Other animals

Mammals

Birds

References

External links

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Health-EU Portal - Nutrition
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