Editing Chewing (section)

{{Redirect|Chew}}
{{short description|Mechanical procedure for crushing the food and its first enzymatic splitting}}
[[File:Macaca arctoides.png|thumb|right|250px|A [[stump-tailed macaque]] using mastication to process tough plant matter]]
'''Chewing''' or '''mastication''' is the process by which [[food]] is [[comminution|crushed and ground]] by the [[teeth]]. It is the first step in the process of [[digestion]], allowing a greater surface area for [[digestive enzyme]]s 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 [[jaw]]s to bring the teeth into intermittent contact, repeatedly [[occlusion (dentistry)|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 (digestion)|bolus]]) is swallowed. It enters the [[esophagus]] and via [[peristalsis]] continues on to the stomach, where the next step of digestion occurs.<ref>{{cite web|title=Prehension, Mastication and Swallowing|url=http://biology.about.com/library/organs/blpathodigest4.htm|access-date=2012-05-24|archive-date=2015-07-15|archive-url=https://web.archive.org/web/20150715020626/http://biology.about.com/library/organs/blpathodigest4.htm|url-status=dead}}</ref> Increasing the number of chews per bite stimulates the production of digestive enzymes and peptides and has been shown to increase diet-induced thermogenesis (DIT) by activating the [[sympathetic nervous system]].<ref name=":0" /> Studies suggest that thorough chewing may facilitate digestion and nutrient absorption, improve insulin secretion and glucose homeostasis, and decrease food intake and levels of self-reported hunger.<ref name=":0">{{Cite journal|last1=Miquel-Kergoat|first1=Sophie|last2=Azais-Braesco|first2=Veronique|last3=Burton-Freeman|first3=Britt|last4=Hetherington|first4=Marion M.|date=2015-11-01|title=Effects of chewing on appetite, food intake and gut hormones: A systematic review and meta-analysis|journal=Physiology & Behavior|volume=151|pages=88–96|doi=10.1016/j.physbeh.2015.07.017|issn=1873-507X|pmid=26188140|doi-access=free}}</ref> [[Chewing gum]] has been around for many centuries; there is evidence that northern Europeans chewed [[Birch tar|birch bark tar]] 9,000 years ago. 

Mastication, as it requires specialized teeth, is mostly a mammalian adaptation that appeared in early [[Synapsid]]s, although some later herbivorous dinosaurs, now extinct, also developed chewing, too. Today only modern mammals chew in the strictest sense of the word, but some fish species exhibit a somewhat similar behavior.  By contrast, mastication is not found in any living birds, amphibians, or reptiles.

[[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<ref name=HolmesEA>{{citation|first=Wendy |last=Holmes |title=Influences on maternal and child nutrition in the highlands of the northern Lao PDR |journal=Asia Pac J Clin Nutr |year=2007 |volume=16 |number=3 |pages=537–545|pmid=17704036}}</ref> (some other animals also premasticate).

[[Cattle]] and some other animals, called [[ruminant]]s, chew food more than once to extract more nutrients. After the first round of chewing, this food is called [[cud]].

[[File:Trodden on chewing gum2.jpg|thumb|A piece of chewing gum after being trodden on.]]