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Eating (also known as consuming) is the ingestion of food. In biology, this is typically done to provide a organism with food energy and and to allow for growth. Animals and other heterotrophs must eat in order to survive – eat other animals, eat plants, 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 Dieting 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".
Most societies also have , , and street food 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."David Grazian (2008), "On the Make: The Hustle of Urban Nightlife", 32 At , , and , 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. of smaller amounts may be consumed between meals. Doctors in the UK recommend three meals a day (with between 400 and 600 calorie 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, it may be proscribed for Muslim adults during the daylight hours of Ramadan.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
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. Hebrew people also adopted this posture for traditional celebrations of Passover.
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.
Eating rapidly leads to obesity and overeating, probably because the feelings of satiety can be slower.
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 level 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.
Cessation of eating within two hours of sleeping can reduce body weight.
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. 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 (CART), the second is α-MSH (α-melanocyte-stimulating hormone).
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If eating and drinking is not possible, as is often the case when recovering from surgery, alternatives are enteral nutrition and parenteral nutrition.Heisler, Jennifer. "Surgery." About.com. N.p., May–June 2010. Web. 13 Mar. 2013.
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