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Amandines de Provence, poster by Leonetto Cappiello, 1900, which shows a woman eating almond cookies

Eating (also known as consuming) is the ingestion of food. In biology, this is typically done to provide a heterotrophic organism with energy and nutrients and to allow for 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, and detritivores eat detritus. Fungi digest organic matter outside their bodies as opposed to animals that digest their food inside their bodies.

For humans, eating is more complex, but is typically an activity of daily living. Physicians and dieticians consider a healthful diet essential for maintaining peak physical condition. Some individuals may limit their amount of nutritional intake. This may be a result of a lifestyle choice: as part of a diet or as religious fasting. Limited consumption may be due to hunger or famine. Overconsumption of calories may lead to obesity and the reasons behind it are myriad, however, its prevalence has led some to declare an "obesity epidemic".

Eating practices among humans

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Women eating biscuits in England
A girl eating a piece of cake

Many homes have a large kitchen area devoted to preparation of meals and food, and may have a dining room, dining hall, or another designated area for eating.

Most societies also have restaurants, food courts, and food vendors so that people may eat when away from home, when lacking time to prepare food, or as a social occasion.[1] At their highest level of sophistication, these places become "theatrical spectacles of global cosmopolitanism and myth."[2] At picnics, potlucks, and food festivals, eating is 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 meals a day.[3] Snacks of smaller amounts may be consumed between meals. Doctors in the UK recommend three meals a day (with between 400 and 600 kcal per meal),[4][5] with four to six hours between.[6] 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)[7] will then amount to some 1800–2000 kcal, which is the average requirement for a regular person.[8]

In jurisdictions under Sharia law, it may be proscribed for Muslim adults during the daylight hours of Ramadan.[9][10][11]

Development in humans

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Newborn babies do not eat adult foods. They survive solely on breast milk or infant formula.[12] 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 foods 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.[13]

  • Eating with fork at a restaurant
    Eating with fork at a restaurant
  • Traditional way of eating in Uzbekistan
    Traditional way of eating in Uzbekistan
  • Girl eating with chopsticks
    Girl eating with chopsticks
  • Ethiopians eating with hands
    Ethiopians eating with hands

Eating positions

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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 at a table.[14][15]

Eating in a reclining position was favored by the Ancient Greeks at a celebration they called a symposium, and this custom was adopted by the Ancient Romans.[16] Ancient Hebrews also adopted this posture for traditional celebrations of Passover.[17]

Compulsive overeating

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Main article: Compulsive overeating

Compulsive overeating, or emotional eating, is "the tendency to eat in response to negative emotions".[18] Empirical studies have indicated that anxiety leads to decreased food consumption in people with normal weight and increased food consumption in the obese.[19]

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.[20]

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.[20]

Hunger and satiety

[edit]
Further information: Hunger (motivational state)

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, enterostatin, leptin and corticotropin-releasing hormone have all been shown to suppress food intake.[21][22]

Eating rapidly leads to obesity and overeating, probably because the feelings of satiety can be slower.[23]

Initiation

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German Shepherd puppy eating out of a human hand

There are numerous signals given off that initiate hunger. There are environmental signals, signals from the gastrointestinal system, and metabolic signals that trigger hunger. The environmental signals come from the body's senses. 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.[24] 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.[25]

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.[24] 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).[24] 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.[26]

Termination

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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.[24] 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, and it controls the rate at which the stomach is emptied.[27] This hormone is thought to be a satiety signal to the brain. Peptide YY 3-36 is a hormone released by the small intestine and it is also used as a satiety signal to the brain.[28] Insulin also serves as a satiety signal to the brain. The brain detects insulin 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 leptin, and leptin suppresses appetite. Long-term satiety signals from adipose tissue regulates short-term satiety signals.[24]

Cessation of eating within two hours of sleeping can reduce body weight.[23]

Role of the brain

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The brain stem can control food intake, because it contains neural circuits that detect hunger and satiety signals from other parts of the body.[24] 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.[24] Instead, they must 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 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.[29] 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).[24]

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 (CART), the second is α-MSH (α-melanocyte-stimulating hormone).[24]

Disorders

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Main article: Eating disorder

Physiologically, eating is generally triggered by hunger, but there are numerous physical and psychological conditions that can affect appetite and disrupt normal eating patterns. These include depression, food allergies, ingestion of certain chemicals, bulimia, anorexia nervosa, pituitary gland malfunction and other endocrine problems, and numerous other illnesses and eating disorders. A chronic lack of nutritious food can cause various illnesses, and will eventually lead to starvation.

While changes in appetite can result from various physical and psychological conditions, including depression, allergies, and anxiety; anorexia and bulimia are specific eating disorders that profoundly impact the entire body.[30] In anorexia nervosa, people restrict their calorie intake out of fear of gaining weight. This malnutrition leads to an unhealthy weight, significantly impacting overall health.[31] Bulimia is characterized by recurrent episodes of binge eating, involving the consumption of a substantial amount of food within a short period. Subsequently, individuals engage in maladaptive behaviors, such as inducing vomiting, excessive physical activity, and using laxatives as compensatory measures.[32]

If eating and drinking is not possible, as is often the case when recovering from surgery, alternatives are enteral[33] nutrition and parenteral nutrition.[34]

Other animals

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Birds

[edit]
This section is an excerpt from Bird § Diet and feeding.[edit]
Illustration of the heads of 16 types of birds with different shapes and sizes of beak
Feeding adaptations in beaks

Birds' diets are varied and often include nectar, fruit, plants, seeds, carrion, and various small animals, including other birds.[35] The digestive system of birds is unique, with a crop for storage and a gizzard that contains swallowed stones for grinding food to compensate for the lack of teeth.[36] Some species such as pigeons and some psittacine species do not have a gallbladder.[37] Most birds are highly adapted for rapid digestion to aid with flight.[38] Some migratory birds have adapted to use protein stored in many parts of their bodies, including protein from the intestines, as additional energy during migration.[39]

Birds that employ many strategies to obtain food or feed on a variety of food items are called generalists, while others that concentrate time and effort on specific food items or have a single strategy to obtain food are considered specialists.[35] Avian foraging strategies can vary widely by species. Many birds glean for insects, invertebrates, fruit, or seeds. Some hunt insects by suddenly attacking from a branch. Those species that seek pest insects are considered beneficial 'biological control agents' and their presence encouraged in biological pest control programmes.[40] Combined, insectivorous birds eat 400–500 million metric tons of arthropods annually.[41]

Nectar feeders such as hummingbirds, sunbirds, lories, and lorikeets amongst others have specially adapted brushy tongues and in many cases bills designed to fit co-adapted flowers.[42] Kiwis and shorebirds with long bills probe for invertebrates; shorebirds' varied bill lengths and feeding methods result in the separation of ecological niches.[35][43] Divers, diving ducks, penguins and auks pursue their prey underwater, using their wings or feet for propulsion,[44] while aerial predators such as sulids, kingfishers and terns plunge dive after their prey. Flamingos, three species of prion, and some ducks are filter feeders.[45][46] Geese and dabbling ducks are primarily grazers.[47][48]

Some species, including frigatebirds, gulls,[49] and skuas,[50] engage in kleptoparasitism, stealing food items from other birds. Kleptoparasitism is thought to be a supplement to food obtained by hunting, rather than a significant part of any species' diet; a study of great frigatebirds stealing from masked boobies estimated that the frigatebirds stole at most 40% of their food and on average stole only 5%.[51] Other birds are scavengers; some of these, like vultures, are specialised carrion eaters, while others, like gulls, corvids, or other birds of prey, are opportunists.[52]

Mammals

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This section is an excerpt from Mammal § Feeding.[edit]
A short-beaked echidna foraging for insects

To maintain a high constant body temperature is energy expensive—mammals therefore need a nutritious and plentiful diet. While the earliest mammals were probably predators, different species have since adapted to meet their dietary requirements in a variety of ways. Some eat other animals—this is a carnivorous diet (and includes insectivorous diets). Other mammals, called herbivores, eat plants, which contain complex carbohydrates such as cellulose. An herbivorous diet includes subtypes such as granivory (seed eating), folivory (leaf eating), frugivory (fruit eating), nectarivory (nectar eating), gummivory (gum eating) and mycophagy (fungus eating). The digestive tract of an herbivore is host to bacteria that ferment these complex substances, and make them available for digestion, which are either housed in the multichambered stomach or in a large cecum.[53] Some mammals are coprophagous, consuming feces to absorb the nutrients not digested when the food was first ingested.[54]: 131–137  An omnivore eats both prey and plants. Carnivorous mammals have a simple digestive tract because the proteins, lipids and minerals found in meat require little in the way of specialised digestion. Exceptions to this include baleen whales who also house gut flora in a multi-chambered stomach, like terrestrial herbivores.[55]

The size of an animal is also a factor in determining diet type (Allen's rule). Since small mammals have a high ratio of heat-losing surface area to heat-generating volume, they tend to have high energy requirements and a high metabolic rate. Mammals that weigh less than about 18 ounces (510 g; 1.1 lb) are mostly insectivorous because they cannot tolerate the slow, complex digestive process of an herbivore. Larger animals, on the other hand, generate more heat and less of this heat is lost. They can therefore tolerate either a slower collection process (carnivores that feed on larger vertebrates) or a slower digestive process (herbivores).[56] Furthermore, mammals that weigh more than 18 ounces (510 g; 1.1 lb) usually cannot collect enough insects during their waking hours to sustain themselves. The only large insectivorous mammals are those that feed on huge colonies of insects (ants or termites).[57]

The hypocarnivorous American black bear (Ursus americanus) vs. the hypercarnivorous polar bear (Ursus maritimus)[58]

Some mammals are omnivores and display varying degrees of carnivory and herbivory, generally leaning in favour of one more than the other. Since plants and meat are digested differently, there is a preference for one over the other, as in bears where some species may be mostly carnivorous and others mostly herbivorous.[59] They are grouped into three categories: mesocarnivory (50–70% meat), hypercarnivory (70% and greater of meat), and hypocarnivory (50% or less of meat). The dentition of hypocarnivores consists of dull, triangular carnassial teeth meant for grinding food. Hypercarnivores, however, have conical teeth and sharp carnassials meant for slashing, and in some cases strong jaws for bone-crushing, as in the case of hyenas, allowing them to consume bones; some extinct groups, notably the Machairodontinae, had sabre-shaped canines.[58]

Some physiological carnivores consume plant matter and some physiological herbivores consume meat. From a behavioural aspect, this would make them omnivores, but from the physiological standpoint, this may be due to zoopharmacognosy. Physiologically, animals must be able to obtain both energy and nutrients from plant and animal materials to be considered omnivorous. Thus, such animals are still able to be classified as carnivores and herbivores when they are just obtaining nutrients from materials originating from sources that do not seemingly complement their classification.[60] For example, it is well documented that some ungulates such as giraffes, camels, and cattle, will gnaw on bones to consume particular minerals and nutrients.[61] Also, cats, which are generally regarded as obligate carnivores, occasionally eat grass to regurgitate indigestible material (such as hairballs), aid with haemoglobin production, and as a laxative.[62]

Many mammals, in the absence of sufficient food requirements in an environment, suppress their metabolism and conserve energy in a process known as hibernation.[63] In the period preceding hibernation, larger mammals, such as bears, become polyphagic to increase fat stores, whereas smaller mammals prefer to collect and stash food.[64] The slowing of the metabolism is accompanied by a decreased heart and respiratory rate, as well as a drop in internal temperatures, which can be around ambient temperature in some cases. For example, the internal temperatures of hibernating Arctic ground squirrels can drop to −2.9 °C (26.8 °F); however, the head and neck always stay above 0 °C (32 °F).[65] A few mammals in hot environments aestivate in times of drought or extreme heat, for example the fat-tailed dwarf lemur (Cheirogaleus medius).[66]

See also

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References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Eating

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Eating is the behavioral and physiological process by which living organisms ingest to obtain essential nutrients, , and materials required for growth, maintenance, and survival. This fundamental activity is driven by homeostatic mechanisms that respond to internal signals of depletion, such as , and is modulated by hormones like and to regulate intake and prevent overconsumption. In humans, eating extends beyond mere sustenance, encompassing sensory pleasure, social interaction, and cultural rituals that shape dietary preferences and meal structures across diverse populations. Biologically, the eating process begins with the sensory detection of , followed by mastication and , which initiate mechanical and chemical breakdown in the digestive to facilitate absorption into the bloodstream. Key regulatory centers in the , particularly the , integrate signals from the gut (e.g., cholecystokinin for ) and to balance caloric intake with expenditure, ensuring metabolic stability. Factors such as fat-free mass, , and palatability of strongly influence the quantity and frequency of meals, with disruptions in these controls contributing to conditions like in environments rich in highly processed, energy-dense foods. Socially and culturally, eating patterns are profoundly shaped by traditions, dynamics, and societal norms, which can promote communal bonding through shared meals or enforce specific taboos and rituals. For instance, in many cultures, meal timing, portion sizes, and choices reflect values around , , and identity, influencing overall nutritional outcomes and vulnerability to diet-related diseases. These influences interact with biological drives, where social cues like portion norms at group settings can override individual signals, potentially leading to . When eating behaviors become dysregulated, they can manifest as eating disorders, serious conditions characterized by severe disturbances in consumption, such as , , and . These disorders affect physical health through , imbalances, and organ damage, while also impacting psychological well-being and social functioning, with higher prevalence among adolescents and young adults. Effective management often requires integrated approaches combining nutritional rehabilitation, , and, in some cases, medications like for bulimia.

Biological Foundations

Definition and Basic Physiology

Eating is the fundamental by which organisms ingest, digest, and absorb from to obtain , support growth, and maintain essential functions. This catabolic process breaks down complex macromolecules such as carbohydrates, proteins, and fats into smaller, absorbable molecules that can enter the bloodstream for cellular use. In multicellular like humans, eating encompasses coordinated actions across the to ensure efficient nutrient extraction and waste elimination. The process initiates with , the entry of food into the , where mechanical breakdown begins through mastication—chewing by the teeth that physically fragments food into smaller particles to increase surface area for enzymatic action. Concurrently, chemical breakdown commences as salivary glands secrete enzymes, notably , which hydrolyzes starches into simpler sugars, while also moistens the food mass. The then manipulates the softened food into a bolus, which is propelled via into the , marking the initial phase of propulsion. From the to the , the upper digestive tract plays a critical role in preliminary processing. The , lined with stratified squamous epithelial tissue, serves as a conduit where —sequential waves of contractions—transports the bolus downward without conscious effort. Upon reaching the , the bolus encounters further mechanical mixing and acidic chemical , but the epithelial lining throughout this segment, including mucous membranes, protects underlying tissues from abrasion and corrosive secretions while facilitating passage. These mechanisms ensure food is adequately prepared for subsequent absorption in the intestines. Evolutionarily, eating traces its origins to the advent of heterotrophy among early life forms around 3.5 billion years ago, when primitive anaerobic cells at hydrothermal vents or in primordial organic-rich environments began fermenting external organic compounds, such as and sugars, for carbon and energy needs. This shift from potential autotrophic self-sufficiency to reliance on pre-formed organics marked a pivotal in microbial , enabling diversification of metabolic strategies. Unlike active eating in heterotrophs, which involves deliberate and breakdown of solid or liquid , some organisms exhibit passive absorption, where dissolved organics diffuse directly across cell membranes without structured consumption, as seen in certain or protists.

Hunger and Satiety Mechanisms

Hunger arises as a multifaceted physiological signal that prompts the initiation of eating, encompassing sensations from contractions, declines in blood glucose levels, and perceptions of an empty gut. contractions, often referred to as hunger pangs, occur rhythmically in the empty through peristaltic waves that serve a function and contribute to the drive to eat. Low blood glucose concentrations trigger these contractions via stimulation of vagal nerve fibers, amplifying the urgency to consume . Empty gut sensations further reinforce through ongoing even in the absence of , creating a visceral cue for replenishment. A seminal experiment demonstrating the link between and was conducted by Walter B. Cannon and A. L. Washburn in 1912, where Washburn swallowed a attached to a recording device to measure gastric contractions while signaling his subjective sensations. The study revealed a direct : contractions intensified precisely when pangs were reported, establishing as a primary peripheral driver of awareness. Satiety, in contrast, manifests as a sensation of fullness that terminates eating, primarily through mechanical and chemical cues from the gastrointestinal tract. Stomach distension activates gastric stretch receptors, which signal the expansion of the organ by ingested food and inhibit further intake on a short-term basis. In the intestines, nutrient detection by specialized sensory neurons responds to the chemical composition of chyme, such as carbohydrates, fats, and proteins, generating feedback that sustains satiety beyond immediate gastric filling. These and signals operate via integrated feedback loops to maintain balance, with short-term mechanisms relying on immediate peripheral inputs like gastric stretch and intestinal sensing to regulate size. Long-term feedback involves signals from that reflect overall stores, modulating the sensitivity to acute cues over days or weeks. These peripheral mechanisms exhibit strong conservation across species, as evidenced by similar gastric contraction patterns in that elicit comparable responses during . In rats, for instance, empty and distension-induced inhibition of feeding mirror processes, underscoring the evolutionary preservation of gastrointestinal signaling for control.

Neural and Hormonal Regulation

The serves as the primary central control center for regulating eating behavior, integrating peripheral signals to maintain . Within the , the arcuate nucleus (ARC) plays a pivotal role by housing two opposing neuronal populations: orexigenic neurons expressing (NPY) and agouti-related peptide (AgRP), which promote and food intake, and anorexigenic neurons expressing pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (), which suppress . These ARC neurons receive inputs from circulating hormones and nutrients, projecting to other hypothalamic regions like the paraventricular nucleus (PVN) and (LH) to orchestrate feeding responses. Disruptions in this ARC-mediated circuitry, such as through genetic mutations, can lead to dysregulated eating patterns. Key hormones modulate these hypothalamic pathways to signal or . , produced primarily by the during , acts as an orexigenic hormone by binding to growth hormone secretagogue receptors (GHS-R) on ARC NPY/AgRP neurons, stimulating and preceding meal initiation. In contrast, , secreted by adipocytes in proportion to fat mass, binds to leptin receptors on ARC POMC neurons to promote and reduce food intake, with its discovery revealing a critical link between and regulation of energy balance. Insulin, released from pancreatic beta cells in response to meals, similarly exerts anorexigenic effects by activating hypothalamic receptors that enhance POMC signaling and inhibit NPY/AgRP activity, contributing to postprandial . Neural pathways further integrate these hormonal signals with sensory and reward information. The relays gastrointestinal signals, such as distension or nutrient detection, from the gut to the nucleus tractus solitarius (NTS) in the , which then projects to the and beyond to modulate feeding. These pathways intersect with reward centers, including the () in the ventral , where release from neurons encodes the motivational drive ("wanting") for , enhancing the incentive value of eating cues independent of homeostatic needs. Recent evidence supports this integration; a 2023 () study demonstrated increased activation in the () during anticipation of high-fat rewards, linking sensory expectation to hedonic valuation and behavioral drive. Disruptions in these regulatory mechanisms underscore their importance. For instance, congenital deficiency, caused by homozygous mutations in the LEP , results in absent signaling, leading to severe hyperphagia, impaired , and early-onset due to unchecked orexigenic drive in the . replacement therapy in such cases normalizes eating behavior, highlighting the hormone's essential role in central . Recent (as of 2024) has identified a novel population of -responsive neurons expressing basonuclin 2 (BNC2) in the arcuate nucleus that acutely suppress food , providing new insights into hypothalamic control of .

Human Eating Practices

Cultural and Social Dimensions

Eating serves as a fundamental aspect of cultural s and social bonding across human societies, often reinforcing community ties and shared identities. In Western cultures, communal meals have long been a key ritual for fostering interpersonal relationships and transmitting values. Research indicates that regular family meals promote emotional and social cohesion, with studies showing positive associations between meal frequency and family dynamics in contemporary Western households. Similarly, in many Indigenous traditions, feast days emphasize collective eating to honor ancestors, celebrate harvests, and strengthen communal bonds. For instance, in communities, seasonal feasts involve sharing traditional foods like and game to commemorate the dead and sustain cultural continuity. These practices highlight how eating transcends mere sustenance, acting as a vehicle for cultural preservation and social unity. Food taboos and etiquette further illustrate the social regulation of eating, varying significantly by cultural context to uphold religious, hygienic, or communal norms. In and , the consumption of is strictly prohibited, viewed as impure and contrary to divine commandments. The Qur'an designates as , explicitly forbidding its intake to maintain spiritual purity. Likewise, Jewish kosher laws in the classify pigs as unclean animals due to their lack of cloven hooves and cud-chewing, reinforcing dietary boundaries that define . In contrast, Ethiopian dining etiquette promotes intimate sharing through , a fermented served communally on a single platter. Hand-feeding morsels, known as gursha, symbolizes respect, affection, and , often performed by hosts toward guests to build trust and reciprocity. Social structures have profoundly influenced eating patterns, including portion sizes, , and dynamics. The 20th-century industrialization shifted traditional eating rhythms from agrarian irregularity to structured three- days, but also spurred snacking as factory work and urban lifestyles demanded portable, quick energy sources. Packaging innovations and time constraints led to increased between-meal consumption, altering portion norms and promoting smaller, frequent intakes over formal . roles have similarly shaped these practices, with women historically bearing primary responsibility for food preparation while exhibiting restraint in consumption to align with societal ideals of . In 1950s , cultural expectations emphasized women's domestic roles in cooking for the family, yet public eating norms often encouraged them to consume less visibly, reflecting pressures to embody slenderness and propriety as depicted in era-specific media and guides. Globalization has accelerated changes in eating habits, particularly through the proliferation of , which has reshaped traditional diets in regions like since the . The influx of Western chains such as and introduced high-calorie, processed options, leading to a decline in staple-based meals like and in favor of burgers and fries. Scholarly analyses link this expansion to broader dietary , with rapid and facilitating the adoption of convenience foods that disrupt indigenous culinary traditions. In countries like and , this shift has increased average caloric intake from animal products and sugars, illustrating how global trade and cultural exchange influence local social eating norms.

Developmental and Behavioral Aspects

Eating behaviors in humans develop progressively from infancy through adulthood, shaped by innate reflexes, environmental influences, and learned associations. In newborns, reflexive responses such as the rooting reflex—where an turns their head toward a touch on the cheek—and the sucking reflex facilitate initial , enabling effective and milk intake shortly after birth. Exclusive breastfeeding is recommended for the first six months, after which complementary solid foods are introduced around six months of age to support nutritional needs while continuing for up to two years or beyond. These early feeding patterns establish foundational habits, with transitions to solids promoting oral motor skill development and texture tolerance. During childhood, picky eating emerges as a common behavioral phase, peaking between ages 2 and 3, often driven by food —a developmental caution toward novel foods that may have evolved as a survival mechanism to avoid potential toxins. Longitudinal studies indicate that this selectivity affects approximately 14-50% of young children but over half recover within 2 years, with most cases resolving by ; persistence is linked to factors like early feeding difficulties or parental pressure. By school age, most children broaden their food acceptance through repeated exposure and social modeling, though a small subset may carry selective habits into later years. In adulthood, eating patterns solidify through habit formation, frequently involving Pavlovian conditioning where environmental cues—such as watching television—become associated with snacking, triggering automatic consumption independent of . These cue-reactivity mechanisms can lead to by overriding signals, as sensory stimuli retrieve memories of pleasurable eating experiences. As individuals age, however, often diminishes due to sensory declines in and smell, contributing to reduced intake and a prevalence of or at-risk status in 20-30% of those over 65 years. Behavioral interventions, such as mindful eating training, offer effective strategies to modify these habits across life stages by enhancing of internal cues like and fullness. A review of multi-component mindfulness-based programs demonstrated their efficacy in reducing behaviors and supporting habit change, with moderate effects on and binge tendencies. These approaches, often involving practices like attentive and non-judgmental of cravings, have shown promise in countering cue-driven in adults and addressing selectivity in children.

Positions and Techniques

Eating positions vary across contexts and cultures, with sitting upright being the most common in modern settings to facilitate and comfort. This posture aligns the vertically, leveraging gravity to minimize gastroesophageal , as demonstrated in a 2015 study where elevating the head of the by 6 inches significantly reduced acid events in patients with . Standing positions are often adopted for informal snacking or quick meals, allowing for mobility during casual consumption like or appetizers. In historical contexts, such as ancient Roman symposia, participants reclined on couches arranged in a U-shape during formal banquets, a practice borrowed from the to signify and status among elites. Techniques for eating encompass a range of utensil uses and manual methods shaped by regional traditions. In , forks were introduced in the 11th century via Byzantine influence in , initially met with resistance as a symbol of excess but gradually adopted for spearing by the 16th century among the upper classes. In , emerged as primary eating tools by the 5th century CE, evolving from cooking implements around 1200 BCE in to facilitate handling small portions of and without cutting at the table. South Asian thali meals, featuring an assortment of dishes served on a single plate, traditionally involve eating with the right hand as finger foods, where diners form and curries into morsels using fingertips to enhance sensory engagement with the meal. Ergonomic benefits of upright sitting include reduced risk of and improved efficiency, with showing that this position lowers esophageal acid exposure compared to reclining or postures. Adaptations for disabilities, such as one-handed utensils with built-up or angled handles, were developed in the mid-20th century to assist individuals with limited , including post-World War II veterans returning with injuries that impaired manual dexterity. The evolutionary shift toward bipedal postures in early hominins, beginning around 4 to 7 million years ago with species, transitioned behaviors from quadrupedal to upright locomotion, freeing the hands for carrying and tools in later species by approximately 2 million years ago.

Health Implications and Disorders

Nutritional Essentials

Eating provides essential macronutrients that form the foundation of energy needs and physiological functions. Carbohydrates, typically comprising 45-65% of total daily intake, serve as the primary source of for the body, fueling cellular processes and . Proteins, recommended at 10-35% of daily , are crucial for tissue repair, production, and immune function. Fats, accounting for 20-35% of intake, support synthesis, integrity, and the absorption of fat-soluble vitamins. Micronutrients, required in smaller quantities, play vital roles in metabolic regulation and disease prevention. Vitamins, such as , are essential for synthesis, which maintains ; its deficiency leads to , a condition first systematically documented in James Lind's 1753 treatise following his 1747 demonstrating citrus fruits' efficacy. Minerals like calcium are critical for and muscle contraction, with inadequate intake contributing to risk. Recommended dietary allowances (RDAs) from recent (WHO) updates, spanning 2020-2025, guide nutrient intake to prevent deficiencies and support health. For instance, WHO recommends limiting sodium to less than 2,000 mg per day for adults to reduce risk. Balanced diet models, such as the U.S. Department of Agriculture's introduced in 2011, promote visual portioning where fruits and occupy half the plate to ensure adequate , vitamins, and minerals alongside grains, proteins, and . Nutrient absorption varies by source, influencing dietary planning. Iron bioavailability is notably higher from heme sources in meat (15-35% absorption) compared to non-heme iron in plants (2-20%), a factor that requires vegetarians to consume higher amounts or pair plant sources with to enhance uptake.

Common Eating Disorders

Eating disorders represent a group of serious psychiatric conditions characterized by persistent disturbances in eating behaviors, body image, and emotional regulation, often leading to significant physical and psychological impairment. The most common clinically recognized eating disorders, as defined in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (), include , , and binge-eating disorder. These disorders typically emerge in or early adulthood, with females disproportionately affected, and are associated with high rates of with other conditions such as depression and anxiety. Early and intervention are crucial, as untreated cases can result in severe medical complications, including cardiovascular issues, gastrointestinal problems, and increased mortality risk. Anorexia nervosa is characterized by severe restriction of energy intake relative to requirements, resulting in a significantly low body weight in the context of age, sex, developmental trajectory, and physical health. Diagnostic criteria per the DSM-5 also require an intense fear of gaining weight or becoming fat, or persistent behavior that interferes with weight gain, even though at a significantly low weight, along with a disturbance in the way body weight or shape is experienced, undue influence of body weight and shape on self-evaluation, or lack of recognition of the seriousness of the low body weight. This disorder often manifests through extreme food avoidance, distorted body image leading to denial of illness severity, and compulsive behaviors like excessive exercise or ritualistic eating patterns. The lifetime prevalence of anorexia nervosa is approximately 0.9% among females and 0.3% among males. Medical consequences include malnutrition, osteoporosis, and bradycardia, underscoring the need for multidisciplinary treatment involving nutritional rehabilitation and psychotherapy. Bulimia nervosa entails recurrent episodes of , defined as consuming an abnormally large amount of food in a discrete period with a sense of lack of control, followed by recurrent inappropriate compensatory behaviors to prevent weight gain, such as self-induced , misuse of laxatives, diuretics, or enemas, , or excessive exercise. According to criteria, these binge-eating and compensatory episodes must occur, on average, at least once weekly for three months, with self-evaluation unduly influenced by body shape and weight. Symptoms commonly include cycles of bingeing and purging, which can lead to electrolyte imbalances, from , and gastrointestinal distress. The disorder is linked to a lifetime of 1-2% in young women, with higher rates observed in community samples of adolescents. Unlike , individuals with bulimia nervosa may maintain a normal or above-normal weight, complicating recognition. Binge-eating disorder, formally recognized as a distinct in the published in , involves recurrent episodes of without regular compensatory behaviors, marked by eating large amounts of food rapidly, eating until uncomfortably full, eating alone due to embarrassment, and feeling disgusted, depressed, or guilty afterward, with associated distress. These episodes occur, on average, at least once weekly for three months, distinguishing it from occasional . This disorder is the most prevalent among the three, affecting 2-3.5% of the global population over their lifetime, and is often comorbid with and mood disorders. Unlike , the absence of purging contributes to weight gain and related health issues such as and . The of these s is multifactorial, with substantial evidence for genetic contributions; twin studies have estimated at 50-80%, indicating a strong inherited component influencing vulnerability. Environmental factors, including such as or , are also implicated, with recent meta-analyses from 2024 confirming elevated risks of development following traumatic experiences, particularly in mediating pathways like . These genetic and environmental interactions highlight the disorders' complex origins, informing targeted prevention efforts. Treatment for common eating disorders emphasizes evidence-based psychotherapies, with cognitive-behavioral therapy (CBT) demonstrating robust efficacy across diagnoses. Meta-analyses indicate CBT achieves remission rates of 40-60% in , , and binge-eating disorder, often outperforming other interventions by addressing maladaptive thoughts about food, , and control. CBT typically involves structured sessions focusing on behavioral experiments, , and relapse prevention, with adjunctive medical monitoring for physical stabilization. While pharmacological options like antidepressants may support symptom management in and binge-eating disorder, remains the cornerstone, yielding sustained improvements in 40-60% of cases at follow-up. Overeating refers to the consumption of in excess of physiological needs, often driven by habitual patterns rather than acute . Compulsive overeating, in particular, involves repetitive, uncontrolled intake of large amounts of without the intense psychological distress or sense of loss of control that characterizes binge-eating disorder. Unlike binge episodes, which are discrete and accompanied by marked shame or guilt, compulsive overeating tends to occur more gradually throughout the day and lacks significant emotional turmoil, though it can still contribute to over time. Obesity arises primarily from a sustained energy imbalance where caloric intake consistently exceeds expenditure, leading to the accumulation of excess body fat. The classifies obesity as a (BMI) of 30 or greater, a threshold established in the based on population health risks. This condition affects approximately 16% of adults globally as of 2022. Key risk factors for obesity include sedentary lifestyles, which reduce daily energy expenditure, and exposure to high-calorie food environments that promote overconsumption. These environmental influences, often termed the "obesogenic" setting, facilitate habitual overeating by making energy-dense foods readily available and affordable. Among the health consequences of obesity, type 2 diabetes is prominent, stemming from obesity-induced insulin resistance where adipose tissue impairs glucose uptake in cells. Cardiovascular disease risk also escalates, as excess lipids from obesity contribute to atherosclerosis by promoting plaque buildup in arteries. These outcomes underscore the metabolic strain of chronic overeating and energy surplus. Interventions for overeating and obesity emphasize lifestyle modifications, such as portion control techniques to regulate intake and prevent excess calories. Pharmacological treatments, including glucagon-like peptide-1 (GLP-1) receptor agonists such as semaglutide and tirzepatide, have emerged as effective options as of 2025, achieving average weight losses of 15-20% in clinical trials and addressing overeating behaviors by enhancing satiety and reducing appetite. For severe cases, bariatric surgery offers substantial outcomes, with patients typically achieving 50-70% excess weight loss that can be sustained long-term when combined with behavioral support.

Eating in Non-Human Animals

Mammalian Feeding Strategies

Mammals exhibit a wide array of feeding strategies adapted to diverse ecological niches, ranging from specialized herbivory to carnivory and omnivory, shaped by anatomical modifications and behavioral patterns that optimize acquisition. These strategies reflect evolutionary responses to availability, with herbivores relying on microbial symbioses for digestion, carnivores on predatory efficiency for animal prey, and omnivores on dietary flexibility for variable resources. Such adaptations highlight the versatility of mammalian and gastrointestinal systems in exploiting different trophic levels. Herbivorous mammals, particularly ruminants like cows, possess a four-chambered stomach comprising the , , , and , which facilitates the breakdown of fibrous material. In the , symbiotic microbes ferment —a key component of cell walls—producing volatile fatty acids as the source for the host. This microbial enables ruminants to derive nutrition from otherwise indigestible , supporting their role as grazers in grasslands and forests. Carnivorous mammals feature sharp, pointed teeth suited for tearing , including elongated canines and premolars that shear meat efficiently, as seen in like lions. Their digestive tracts are relatively short compared to body length, allowing rapid passage and absorption of nutrient-dense animal proteins while minimizing bacterial overgrowth in the gut. Lions exemplify pack behaviors, where coordinated group efforts enable the takedown of large prey such as zebras or wildebeests, enhancing feeding success in open savannas. Omnivorous mammals, including many , maintain flexible diets incorporating both and animal matter, supported by versatile mechanics that allow varied chewing motions. In like chimpanzees, molars with mixed cusp patterns crush fruits and pierce , reflecting adaptations to eclectic in arboreal environments. This dietary breadth, combined with muscle flexibility, enables efficient of heterogeneous foods, from seeds to small vertebrates. Specialized feeding behaviors further diversify mammalian strategies; for instance, nectar-feeding bats employ elongated tongues with hair-like papillae that become erect during feeding to mop up liquid from flowers. Similarly, squirrels engage in food caching, burying nuts and seeds in scattered locations to store surpluses against seasonal scarcity, a behavior that also aids . Mammalian evolved from an insectivorous base around 200 million years ago during the , when early mammals developed differentiated teeth for piercing and grinding exoskeletons of , diverging from reptilian ancestors. This foundational adaptation laid the groundwork for subsequent radiations into herbivory and carnivory, with tooth complexity increasing to match dietary shifts over geological time.

Avian Foraging Behaviors

Avian foraging behaviors are specialized adaptations that enable birds to efficiently capture and process while maintaining the lightweight structures essential for flight. These behaviors encompass a range of techniques tailored to diverse diets, from seeds and to , often leveraging morphology, sensory acuity, and social coordination. Unlike terrestrial mammals, birds prioritize rapid intake and to minimize energy expenditure during , allowing them to exploit ephemeral resources in aerial or arboreal environments. Beak adaptations play a central role in avian foraging, with variations shaped by dietary needs. In of the , observed during his 1835 voyage, ground finches exhibit deep and wide s that facilitate cracking hard by reducing stress concentrations during application. Similarly, hummingbirds possess elongated, slender s for probing deep into flowers to extract , a structure that enhances volumetric capacity for fluid intake and supports their high-metabolic hover-feeding lifestyle. Foraging strategies further diversify based on and prey mobility. Chickens employ ground pecking and to uncover and , a that correlates with overall range use and exploration in free-range settings. In contrast, swifts capture aerial during sustained flight, relying on enhanced morphology and broad visual fields for precise detection and of fast-moving targets. These tactics underscore the integration of locomotion and in avian predation. Digestive adaptations complement by optimizing nutrient extraction without heavy dental structures. Seed-eating birds utilize the , a muscular organ that grinds ingested material through mechanical action, often aided by ingested grit, to break down tough husks and improve digestibility. Pigeons, meanwhile, employ the as a temporary storage pouch at the base, softening through moisture and initiating pre-fermentation before proventricular processing. Social dynamics enhance efficiency in many species, particularly through . European starlings (Sturnus vulgaris) forage in groups where increased density promotes social scanning and information sharing, allowing individuals to locate food patches more rapidly without heightened predation risk. Migration profoundly influences avian , necessitating pre-flight loading to meet caloric demands of long-distance travel. Birds accumulate reserves through hyperphagic diets rich in high-energy foods, enabling non-stop flights where provides the primary fuel, supplemented by . Recent GPS-tracking studies from the have quantified these needs, revealing that species like thrush nightingales expend consistent energy rates over 12-hour flights, with optimal composition reducing overall metabolic costs by up to 11%.

Invertebrate and Other Animal Patterns

Eating patterns among and other non-mammalian, non-avian animals exhibit remarkable diversity, adapted to their environments and physiologies. In sponges ( Porifera), filter-feeding occurs passively through a network of pores and canals, where water is drawn in via flagellated choanocytes that trap bacteria and organic particles for , filtering up to 90% of bacteria from incoming water. This mechanism, one of the earliest metazoan feeding strategies, relies on ambient currents without active pursuit. In contrast, spiders (class Arachnida) employ active predation, injecting to immobilize prey before regurgitating externally to liquefy tissues, which are then sucked up through their sucking , enabling consumption of a wide range of arthropods and . Reptiles demonstrate varied feeding adaptations tied to their ectothermic lifestyles. Snakes, such as pythons and vipers, swallow prey whole using a highly kinetic where the lower disarticulates at the , allowing extreme gape expansion up to 150% of head width to accommodate large meals like or birds. Herbivorous reptiles like the (Iguana iguana) rely on microbial fermentation in an enlarged , where break down plant cell walls, providing 30-40% of their energy from despite a simple . Fish feeding mechanisms often involve specialized oral and branchial structures. In planktivorous species like the Atlantic herring (Clupea harengus), elongate gill rakers form a fine sieve that filters zooplankton from water pumped through the mouth and over the gills, capturing particles as small as 10-100 micrometers with high efficiency during continuous ram ventilation. Predatory sharks, such as the great white (Carcharodon carcharias), use robust, protrusible jaws armed with serrated teeth to tear flesh from large prey like seals, employing biting and shaking motions to dismember tissue before swallowing chunks whole. Amphibians, particularly anurans, showcase projectile feeding for terrestrial . Frogs like the (Lithobates catesbeianus) project their tongues up to 1.5 times body length at speeds exceeding 3 m/s via of the hyoid apparatus, achieving capture success rates around 70-80% in studies of prey interception. Unique parasitic patterns further highlight evolutionary innovations in nutrient acquisition. Tapeworms (class ), such as , lack a digestive tract and absorb pre-digested nutrients directly across their syncytial tegument from the host's intestine via diffusion and , optimizing surface area with microtriches for maximal uptake. This endoparasitic lifestyle traces back over 500 million years to the , predating many free-living bilaterians.

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