Chewing or mastication is the process by which food is crushed and ground by the teeth. It is the first step in the process of digestion, allowing a greater surface area for digestive enzymes to break down the foods.
During the mastication process, the food is positioned by the cheek and tongue between the teeth for grinding. The muscles of mastication move the jaws to bring the teeth into intermittent contact, repeatedly occluding and opening. As chewing continues, the food is made softer and warmer, and the enzymes in saliva begin to break down carbohydrates in the food. After chewing, the food (now called a bolus) is swallowed. It enters the esophagus and via peristalsis continues on to the stomach, where the next step of digestion occurs.[1] Increasing the number of chews per bite increases relevant gut hormones.[2] Studies suggest that chewing may decrease self-reported hunger and food intake.[2]Chewing gum has been around for many centuries; there is evidence that northern Europeans chewed birch bark tar 9,000 years ago.
Chewing, needing specialized teeth, is mostly a mammalian adaptation that appeared in early Synapsids, though some later herbivorous dinosaurs, since extinct, had developed chewing too. Nowadays, only mammals chew in the strict sense of the word, though some fishes have a somewhat similar behavior. Neither birds, nor amphibians or any living reptiles chew.
Premastication is sometimes performed by human parents for infants who are unable to do so for themselves. The food is masticated in the mouth of the parent into a bolus and then transferred to the infant for consumption[3] (some other animals also premasticate).
Cattle and some other animals, called ruminants, chew food more than once to extract more nutrients. After the first round of chewing, this food is called cud.
Chewing is primarily an unconscious (semi-autonomic) act, but can be mediated by higher conscious input. The motor program for mastication is a hypothesized central nervous system function by which the complex patterns governing mastication are created and controlled.
It is thought that feedback from proprioceptive nerves in teeth and the temporomandibular joints govern the creation of neural pathways, which in turn determine duration and force of individual muscle activation (and in some cases muscle fiber groups as in the masseter and temporalis).
This motor program continuously adapts to changes in food type or occlusion.[4] This adaptation is a learned skill that may sometimes require relearning to adapt to loss of teeth or to dental appliances such as dentures.
It is thought that conscious mediation is important in the limitation of parafunctional habits as most commonly, the motor program can be excessively engaged during periods of sleep and times of stress. It is also theorized that excessive input to the motor program from myofascial pain or occlusal imbalance can contribute to parafunctional habits.
Chewing stimulates saliva production and increases sensory perception of the food being eaten, controlling when the food is swallowed.[5] Evidence from one study suggests that chewing almonds 25-40 times kept people fuller while also allowing them to get more nutrients out of the almonds. The researchers also suggest that this is likely to be the case in other foods.[6] A 2015 systemic review found evidence that chewing can decrease self-reported hunger and therefore food intake.[7] Eating food which does not require chewing, by choice or due to medical reasons as tooth loss, is known as a soft diet. Such a diet may lead to inadequate nutrition due to a reduction in fruit and vegetable intake.[8]
Chewing also stimulates the hippocampus and is necessary to maintain its normal function.[9] Chewing stimulates hippocampal neurogenesis in both humans and mice.[10]
Chewing is largely an adaptation for mammalianherbivory. Carnivores generally chew very little or swallow their food whole or in chunks.[11] This act of gulping food (or medicine pills) without chewing has inspired the English idiom "wolfing it down".
Other animals such as cows chew their food for long periods to allow for proper digestion in a process known as rumination. Rumination in cows has been shown by researchers to intensify during the night. They concluded that cows chewed more intently in the night time compared to the morning.[12]
Ornithopods, a group of dinosaurs including the Hadrosaurids ("duck-bills"), developed teeth analogous to mammalian molars and incisors during the Cretaceous period; this advanced, cow-like dentition allowed the creatures to obtain more nutrients from the tough plant life. This may have given them the advantage needed to compete with the formidable sauropods, who depended on their massive gastrointestinal tracts to digest food without grinding it,[13] in their ecological niches. They eventually became some of the most successful animals on the planet until the Cretaceous–Paleogene extinction event wiped them out.
The process of chewing has, by analogy, been applied to machinery. The U.S. Forest Service uses a machine called a masticator (also called a forestry mulching machine) to "chew" through brush and timber in order to clear firelines in advance of a wildfire.[14]
A cold press juicer uses the mastication process to extract juice from fruit and vegetable without the loss of oxygen or heat-sensitive nutrients as there is less friction involved.[15]
↑ Holmes, Wendy (2007), "Influences on maternal and child nutrition in the highlands of the northern Lao PDR", Asia Pac J Clin Nutr, 16 (3): 537–545, PMID17704036
↑ N'Gom, Papa Ibrahima; Woda, Alain (June 2002). "Influence of impaired mastication on nutrition". The Journal of Prosthetic Dentistry. 87 (6): 667–673. doi:10.1067/mpr.2002.123229. PMID12131890.
↑ Smith, Natalie, Miquel-Kergoat, Sophie, and Thuret, Sandrine. 'The Impact of Mastication on Cognition: Evidence for Intervention and the Role of Adult Hippocampal Neurogenesis'. 1 Jan. 2015: 115 – 123.
The stomach is a muscular, hollow organ in the upper gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach is involved in the gastric phase of digestion, following the cephalic phase in which the sight and smell of food and the act of chewing are stimuli. In the stomach a chemical breakdown of food takes place by means of secreted digestive enzymes and gastric acid.
Peristalsis is a type of intestinal motility, characterized by radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an anterograde direction. Peristalsis is progression of coordinated contraction of involuntary circular muscles, which is preceded by a simultaneous contraction of the longitudinal muscle and relaxation of the circular muscle in the lining of the gut.
Digestion is the breakdown of large insoluble food compounds into small water-soluble components so that they can be absorbed into the blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream. Digestion is a form of catabolism that is often divided into two processes based on how food is broken down: mechanical and chemical digestion. The term mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed by digestive enzymes. Mechanical digestion takes place in the mouth through mastication and in the small intestine through segmentation contractions. In chemical digestion, enzymes break down food into the small compounds that the body can use.
Swallowing, also called deglutition or inglutition in scientific contexts, is the process in the body of a human or other animal that allows for a substance to pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. Swallowing is an important part of eating and drinking. If the process fails and the material goes through the trachea, then choking or pulmonary aspiration can occur. In the human body the automatic temporary closing of the epiglottis is controlled by the swallowing reflex.
Eating 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.
Ruminants are herbivorous grazing or browsing artiodactyls belonging to the suborder Ruminantia that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The process, which takes place in the front part of the digestive system and therefore is called foregut fermentation, typically requires the fermented ingesta to be regurgitated and chewed again. The process of rechewing the cud to further break down plant matter and stimulate digestion is called rumination. The word "ruminant" comes from the Latin ruminare, which means "to chew over again".
Chyme or chymus is the semi-fluid mass of partly digested food that is expelled by a person's or another animal's stomach, through the pyloric valve, into the duodenum.
Cud is a portion of food that returns from a ruminant's stomach to the mouth to be chewed for the second time. More precisely, it is a bolus of semi-degraded food regurgitated from the reticulorumen of a ruminant. Cud is produced during the physical digestive process of rumination.
Vegetable juice is a juice drink made primarily of blended vegetables and also available in the form of powders. Vegetable juice is often mixed with fruits such as apples or grapes to improve flavor. It is often touted as a low-sugar alternative to fruit juice, although some commercial brands of vegetable juices use fruit juices as sweeteners, and may contain large amounts of sodium.
A milk substitute is any substance that resembles milk and can be used in the same ways as milk. Such substances may be variously known as non-dairy beverage, nut milk, grain milk, legume milk, mock milk and alternative milk.
Isomaltulose is a disaccharide carbohydrate composed of glucose and fructose. It is naturally present in honey and sugarcane extracts and is also produced industrially from table sugar (sucrose) and used as a sugar alternative.
Oropharyngeal dysphagia is the inability to empty material from the oropharynx into the esophagus as a result of malfunction near the esophagus. Oropharyngeal dysphagia manifests differently depending on the underlying pathology and the nature of the symptoms. Patients with dysphagia can experience feelings of food sticking to their throats, coughing and choking, weight loss, recurring chest infections, or regurgitation. Depending on the underlying cause, age, and environment, dysphagia prevalence varies. In research including the general population, the estimated frequency of oropharyngeal dysphagia has ranged from 2 to 16 percent.
Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue and can also serve as a fuel source. As a fuel, proteins provide as much energy density as carbohydrates: 4 kcal per gram; in contrast, lipids provide 9 kcal per gram. The most important aspect and defining characteristic of protein from a nutritional standpoint is its amino acid composition.
Baby-led weaning is an approach to adding complementary foods to a baby's diet of breast milk or formula. BLW facilitates oral motor development and strongly focuses on the family meal, while maintaining eating as a positive, interactive experience. Baby-led weaning allows babies to control their solid food consumption by "self-feeding" from the start of their experience with food. The term weaning does not imply giving up breast milk or formula, but simply indicates the introduction of foods other than breast milk or formula.
Aphagia is the inability or refusal to swallow. The word is derived from the Ancient Greek prefix α, meaning "not" or "without," and the suffix φαγία, derived from the verb φαγεῖν, meaning "to eat." It is related to dysphagia which is difficulty swallowing, and odynophagia, painful swallowing. Aphagia may be temporary or long term, depending on the affected organ. It is an extreme, life-threatening case of dysphagia. Depending on the cause, untreated dysphagia may develop into aphagia.
Hunger is a sensation that motivates the consumption of food. The sensation of hunger typically manifests after only a few hours without eating and is generally considered to be unpleasant. Satiety occurs between 5 and 20 minutes after eating. There are several theories about how the feeling of hunger arises. The desire to eat food, or appetite, is another sensation experienced with regard to eating.
Pea protein is a food product and protein supplement derived and extracted from yellow and green split peas, Pisum sativum. It can be used as a dietary supplement to increase an individual's protein or other nutrient intake, or as a substitute for other food products. As a powder, it is used as an ingredient in food manufacturing, such as a thickener, foaming agent, or an emulsifier.
The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion. Digestion involves the breakdown of food into smaller and smaller components, until they can be absorbed and assimilated into the body. The process of digestion has three stages: the cephalic phase, the gastric phase, and the intestinal phase.
Sham feeding is any procedure that mimics normal food consumption but where food and drink are not actually digested or absorbed. It is generally used in experiments studying hunger, eating or digestion, and is a predominant method used in studying binge eating disorder. In animal research it often involves inserting a tube into either the oesophagus or stomach, that leaks out anything that has been swallowed. Animals who are sham fed in this manner eat and swallow almost continually without becoming satiated. Chewing gum can also be considered sham feeding, as whilst very-little or no nutrients are being absorbed into the body, the process of chewing still stimulates digestive system nerves which trigger the release of gastrointestinal hormones, and also increase the production of both saliva and pancreatic secretions. In human studies a process known as modified sham feeding (MSF) is typically used, which involves smelling, tasting and chewing food, then spitting it out when it would normally be swallowed.
Tea and toast syndrome is a form of malnutrition commonly experienced by elderly people who are unable to prepare meals and tend to themselves. The term is not intrinsic to tea or bread products only; rather, it describes limited dietary patterns which lead to reduced calories resulting in a deficiency of vitamins and other nutrients. This can contribute to a gradual loss of wellness and muscle due to poor protein intake. In elderly individuals with a low GFR, the syndrome may manifest itself as hyponatremia, a low concentration of the electrolyte sodium in the bloodstream. This is attributed to drinking a large amount of water while consuming a diet poor in salt and protein. Hyponatremia can lead to various neurological problems ranging from headaches and a decreased ability to think, to seizures and coma in the most severe cases.
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