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Eating

life science Maturity 5-7 Next article →

Eating, also known as ingestion, is the process of taking in food. In biology, this process is vital for heterotrophic organisms. These organisms must consume food to obtain energy and nutrients for growth and survival. Different organisms have different dietary strategies. Carnivores eat other animals, while herbivores consume only plants. Omnivores eat a mixture of both plant and animal matter. Detritivores feed on detritus, which is dead organic matter. Fungi are unique because they digest organic matter outside their bodies. In contrast, animals digest their food inside their bodies.

German Shepherd puppy eating out of a human hand
German Shepherd puppy eating out of a human hand

For humans, eating is a complex activity of daily living. Most people consume two or three meals a day, sometimes supplemented by snacks. In the United Kingdom, doctors recommend three meals daily with four to six hours between them. Each meal should ideally contain between 400 and 600 kcal. A well-balanced plate often consists of half vegetables, one-quarter protein, and one-quarter carbohydrates. This pattern provides an average requirement of 1800 to 2000 kcal per day. Dietary habits can also be influenced by religious practices. For example, under Sharia law, Muslim adults may fast during the daylight hours of Ramadan.

Human eating habits change significantly during early development. Newborn babies cannot eat adult foods. They survive solely on breast milk or infant formula. Because they have few teeth and immature digestive systems, infants often eat pureed foods. Most infants do not transition to adult food until they are between six and eight months old. Between 8 and 12 months, the digestive system improves, and many babies begin eating finger foods. By 18 months, most babies have enough teeth and a mature enough system to eat like adults. Learning to eat is often a messy process. Most children do not master eating etiquette until they are five or six years old.

Cultural traditions also dictate how and where people eat. In many Middle Eastern countries, sitting on the floor is common and believed to be healthier. Historical customs show that eating positions have long varied. The Ancient Greeks favored a reclining position during celebrations called symposia. The Ancient Romans adopted this reclining custom. The Ancient Hebrews also used this posture for traditional Passover celebrations. Today, eating remains a social cornerstone. People gather for picnics, potlucks, and food festivals. In many societies, restaurants and food vendors provide meals when people are away from home or lack time to cook.

Amandines de Provence, poster by Leonetto Cappiello, 1900
Amandines de Provence, poster by Leonetto Cappiello, 1900

Eating is controlled by a complex physiological system involving hunger and satiety. Hunger is initiated by environmental, gastrointestinal, and metabolic signals. Environmental signals include the smell, sight, or thought of food. The stomach initiates hunger signals through the release of the peptide hormone ghrelin. This hormone signals the brain to increase appetite. Metabolic signals occur when the body detects low fuel levels. The brain monitors glucose levels, a process called glucoprivation. The liver monitors the body for both glucose and lipid drops, known as lipoprivation. These signals ensure the body receives necessary nutrients.

Satiety, or the feeling of fullness, is controlled by many different signals. Short-term satiety comes from the head, stomach, intestines, and liver. The hormone cholecystokinin is secreted by the duodenum to control stomach emptying. The small intestine releases Peptide YY 3-36 to signal satiety to the brain. Insulin also acts as a signal, indicating that nutrients are being absorbed into cells. Long-term satiety is regulated by adipose tissue, which is body fat. This tissue secretes the hormone leptin to suppress appetite. The brain stem also plays a role by containing neural circuits that detect these hunger and satiety signals. In the hypothalamus, peptides like melanin concentrating hormone (MCH) and orexin promote hunger. Conversely, the arcuate nucleus uses peptides like CART and α-MSH to suppress it.

Sometimes, eating patterns can become disrupted by physical or psychological conditions. Emotional eating is the tendency to eat in response to negative emotions. Research suggests that obese individuals may be more emotionally reactive. Studies by Lowe and Fisher found that while obese individuals may not eat more during meals, they often eat more snacks between meals. This may be because meals are often social, while snacks are eaten alone. Other serious conditions include eating disorders like anorexia nervosa and bulimia. People with anorexia nervosa restrict calories due to a fear of weight gain. Those with bulimia engage in binge eating followed by compensatory behaviors like vomiting. Other factors, such as depression, allergies, or endocrine problems, can also affect appetite.

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File:Amandines de Provence, poster by Leonetto Cappiello, 1900.jpg
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