Editing Human nutrition (section)

=== Fat ===
{{more medical citations needed|section|date=April 2019}}
{{Main|Fat}}

A molecule of dietary fat typically consists of several [[fatty acid]]s (containing long chains of carbon and hydrogen atoms), bonded to a [[glycerol]]. They are typically found as [[triglyceride]]s (three fatty acids attached to one glycerol backbone). Fats may be classified as [[saturated fat|saturated]] or [[unsaturated fat|unsaturated]] depending on the chemical structure of the fatty acids involved. Saturated fats have all of the [[carbon atoms]] in their fatty acid chains bonded to [[hydrogen atom]]s, whereas unsaturated fats have some of these carbon atoms [[Double bond|double-bonded]], so their molecules have relatively fewer hydrogen atoms than a saturated fatty acid of the same length. Unsaturated fats may be further classified as monounsaturated (one double-bond) or polyunsaturated (many double-bonds). Furthermore, depending on the location of the double-bond in the fatty acid chain, unsaturated fatty acids are classified as [[omega-3]] or [[omega-6]] fatty acids. [[Trans fat]]s are a type of unsaturated fat with ''trans''-isomer bonds; these are rare in nature and in foods from natural sources; they are typically created in an industrial process called (partial) [[hydrogenation]]. There are nine kilocalories in each gram of fat. Fatty acids such as [[conjugated linoleic acid]], [[catalpic acid]], [[eleostearic acid]] and [[punicic acid]], in addition to providing energy, represent potent immune modulatory molecules.<ref>{{cite book | author=National Research Council Committee on Diet and Health | editor-last1=Motulsky | editor-first1=Arno G. | editor-last2=Bierman | editor-first2=Edwin L. | editor-last3=Goodman | editor-first3=DeWitt S. | editor-last4=Mccormick | editor-first4=Donald B. | editor-last5=Arnaud | editor-first5=Claude D. | editor-last6=Iii | editor-first6=John C. Bailar | editor-last7=Blackburn | editor-first7=Henry | editor-last8=Bray | editor-first8=George A. | editor-last9=Carroll | editor-first9=Kenneth K. | editor-last10=Howe | editor-first10=Geoffrey R. | editor-last11=Hurley | editor-first11=Lucille S. | editor-last12=Kolonel | editor-first12=Laurence N. | editor-last13=Mcgill | editor-first13=Henry C. | editor-last14=Miller | editor-first14=Anthony B. | editor-last15=Page | editor-first15=Lot B. | editor-last16=Schieken | editor-first16=Richard M. | editor-last17=Shekelle | editor-first17=Richard B. | editor-last18=Tobian | editor-first18=Louis | editor-last19=Williams | editor-first19=Eleanor R. | display-editors=0 | date=1989 | chapter=Fats and Other Lipids | pages=159–258 | chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK218759/ | title=Diet and health: Implications for reducing chronic disease risk | url=https://www.ncbi.nlm.nih.gov/books/NBK218743/pdf/Bookshelf_NBK218743.pdf#page=176 | publication-place=Washington, DC | publisher=National Academies Press | language=en | doi=10.17226/1222 | doi-access=free | isbn=978-0-309-03994-9 | oclc=19457013 | pmid=25032333}} Also available from [https://nap.nationalacademies.org/read/1222/chapter/10 nationalacademies.org], with page numbers, but with Greek characters [[transliteration|transliterated]].</ref><ref>{{Cite journal | last1=Field | first1=Catherine J | last2=Robinson | first2=Lindsay | date=July 2019 | title=Dietary Fats | url=https://linkinghub.elsevier.com/retrieve/pii/S2161831322004136 | journal=Advances in Nutrition | language=en | volume=10 | issue=4 | pages=722–724 | doi=10.1093/advances/nmz052 | pmc=6628852 | pmid=31147674}}</ref>

Saturated fats (typically from animal sources) have been a staple in many world cultures for millennia. Unsaturated fats (e. g., vegetable oil) are considered healthier, while trans fats are to be avoided. Saturated and some trans fats are typically solid at room temperature (such as [[butter]] or [[lard]]), while unsaturated fats are typically liquids (such as [[olive oil]] or [[flaxseed oil]]). Trans fats are very rare in nature, and have been shown to be highly detrimental to human health, but have properties useful in the [[food processing]] industry, such as rancidity resistance.<ref>{{Cite journal | last=Klonoff | first=David C. | date=24 June 2016 | title=Replacements for Trans Fats—Will There Be an Oil Shortage? | pmc=2769584 | journal=Journal of Diabetes Science and Technology | language=en | volume=1 | issue=3 | pages=415–22 | doi=10.1177/193229680700100316 | pmid=19885099}}</ref>

==== Essential fatty acids ====
{{Main|Essential fatty acids}}
{{more medical citations needed|section|date=February 2020}}

Most fatty acids are non-essential, meaning the body can produce them as needed, generally from other fatty acids and always by expending energy to do so. However, in humans, at least two fatty acids are [[essential fatty acid|essential]] and must be included in the diet. An appropriate balance of essential fatty acids—[[omega-3]] and [[omega-6 fatty acid]]s—seems also important for health, although definitive experimental demonstration has been elusive. Both of these "omega" long-chain [[unsaturated fat|polyunsaturated fatty acids]] are [[substrate (biochemistry)|substrates]] for a class of [[eicosanoid]]s known as [[prostaglandin]]s, which have roles throughout the human body.<ref name="kaur-2014" />

The omega-3 [[eicosapentaenoic acid]] (EPA), which can be made in the human body from the omega-3 essential fatty acid [[alpha-linolenic acid]] (ALA), or taken in through marine food sources, serves as a building block for series 3 prostaglandins (e.g., weakly [[Inflammation|inflammatory]] PGE3). The [[Dihomo-γ-linolenic acid|omega-6 dihomo-gamma-linolenic acid]] (DGLA) serves as a building block for series 1 prostaglandins (e.g. anti-inflammatory PGE1), whereas [[arachidonic acid]] (AA) serves as a building block for series 2 [[prostaglandin]]s (e.g. pro-inflammatory PGE 2). Both DGLA and AA can be made from the omega-6 [[linoleic acid]] (LA) in the human body, or can be taken in directly through food.<ref name="kaur-2014">{{Cite journal | last1=Kaur | first1=Narinder | last2=Chugh | first2=Vishal | last3=Gupta | first3=Anil K. | date=October 2014 | title=Essential fatty acids as functional components of foods- a review | journal=Journal of Food Science and Technology | language=en | volume=51 | issue=10 | pages=2289–2303 | doi=10.1007/s13197-012-0677-0 | issn=0022-1155 | pmc=4190204 | pmid=25328170}}</ref> An appropriately balanced intake of omega-3 and omega-6 partly determines the relative production of different [[prostaglandin]]s. In industrialized societies, people typically consume large amounts of processed vegetable oils, which have reduced amounts of the essential fatty acids along with too much of omega-6 fatty acids relative to omega-3 fatty acids.<ref>{{cite journal | last1=Krupa | first1=Kristina N. | title=Omega-3 Fatty Acids | date=2024 | website=StatPearls | url=http://www.ncbi.nlm.nih.gov/books/NBK564314/ | access-date=2024-08-12 | place=Treasure Island (FL) | publisher=StatPearls Publishing | pmid=33231984 | last2=Fritz | first2=Kristina | last3=Parmar | first3=Mayur}}</ref>

The conversion rate of omega-6 DGLA to AA largely determines the production of the prostaglandins PGE1 and PGE2. Omega-3 EPA prevents AA from being released from membranes, thereby skewing prostaglandin balance away from pro-inflammatory PGE2 (made from AA) toward anti-inflammatory PGE1 (made from DGLA). The conversion (desaturation) of DGLA to AA is controlled by the enzyme [[desaturase|delta-5-desaturase]], which in turn is controlled by hormones such as [[insulin]] (up-regulation) and [[glucagon]] (down-regulation).