Editing Fat (section)

== Metabolism ==
{{See also|Fatty acid metabolism}}
{{main | Lipid metabolism}}

The [[pancreatic lipase]] acts at the ester bond, hydrolyzing the bond and "releasing" the fatty acid. In triglyceride form, lipids cannot be absorbed by the [[duodenum]]. Fatty acids, monoglycerides (one glycerol, one fatty acid), and some diglycerides are absorbed by the duodenum, once the triglycerides have been broken down.

In the [[intestine]], following the secretion of [[lipase]]s and [[bile]], triglycerides are split into monoacylglycerol and free fatty acids in a process called [[lipolysis]]. They are subsequently moved to absorptive [[enterocyte]] cells lining the intestines. The triglycerides are rebuilt in the enterocytes from their fragments and packaged together with [[cholesterol]] and proteins to form [[chylomicron]]s. These are excreted from the cells and collected by the lymph system and transported to the large vessels near the heart before being mixed into the blood. Various tissues can capture the chylomicrons, releasing the triglycerides to be used as a source of energy. Liver cells can synthesize and store triglycerides. When the body requires [[fatty acid]]s as an energy source, the hormone [[glucagon]] signals the breakdown of the triglycerides by [[hormone-sensitive lipase]] to release free fatty acids. As the [[brain]] cannot utilize fatty acids as an energy source (unless converted to a [[ketone]]),<ref>{{Cite journal|doi = 10.1186/cc10020|pmid = 21489321|pmc = 3219306|title = Clinical review: Ketones and brain injury|journal = Critical Care|volume = 15|issue = 2|page = 219|year = 2011|last1 = White|first1 = Hayden|last2 = Venkatesh|first2 = Balasubramanian | doi-access=free}}</ref> the [[glycerol]] component of triglycerides can be converted into [[glucose]], via [[gluconeogenesis]] by conversion into [[dihydroxyacetone phosphate]] and then into [[glyceraldehyde 3-phosphate]], for brain fuel when it is broken down. Fat cells may also be broken down for that reason if the brain's needs ever outweigh the body's.

Triglycerides cannot pass through cell membranes freely. Special enzymes on the walls of blood vessels called [[lipoprotein lipase]]s must break down triglycerides into free fatty acids and glycerol. Fatty acids can then be taken up by cells via [[fatty acid transport proteins]] (FATPs).

Triglycerides, as major components of [[very-low-density lipoprotein]] (VLDL) and [[chylomicron]]s, play an important role in [[metabolism]] as energy sources and transporters of dietary fat. They contain more than twice as much energy (approximately 9{{nbs}}kcal/g or 38{{nbs}}[[Joules|kJ]]/g) as [[carbohydrate]]s (approximately 4{{nbs}}kcal/g or 17{{nbs}}kJ/g).<ref name="drummond">{{cite book|last1=Drummond|first1=K. E.|last2=Brefere|first2=L. M.|date=2014|title=Nutrition for Foodservice and Culinary Professionals|edition=8th|publisher=John Wiley & Sons|isbn=978-0-470-05242-6}}</ref>