Editing Antioxidant (section)

== Levels in food ==
{{further|List of antioxidants in food|Polyphenol antioxidant}}
[[Image:Vegetarian diet.jpg|upright|thumb|Fruits and vegetables are good sources of antioxidant vitamins C and E.]]

Antioxidant vitamins are found in vegetables, fruits, eggs, legumes and nuts. Vitamins A, C, and E can be destroyed by long-term storage or prolonged cooking.<ref>{{Cite journal |vauthors=Rodriguez-Amaya DB |year=2003 |title=Food carotenoids: analysis, composition and alterations during storage and processing of foods |journal=Forum of Nutrition |volume=56 |pages=35–7 |pmid=15806788}}</ref> The effects of cooking and food processing are complex, as these processes can also increase the [[bioavailability]] of antioxidants, such as some carotenoids in vegetables.<ref>{{Cite journal |vauthors=Maiani G, Castón MJ, Catasta G, Toti E, Cambrodón IG, Bysted A, Granado-Lorencio F, Olmedilla-Alonso B, Knuthsen P, Valoti M, Böhm V, Mayer-Miebach E, Behsnilian D, Schlemmer U |date=September 2009 |title=Carotenoids: actual knowledge on food sources, intakes, stability and bioavailability and their protective role in humans |url=https://openagrar.bmel-forschung.de/receive/import_mods_00002107 |url-status=dead |journal=Molecular Nutrition & Food Research |volume=53 |issue=Suppl 2 |pages=S194–218 |doi=10.1002/mnfr.200800053 |pmid=19035552 |archive-url=https://web.archive.org/web/20180927113314/https://openagrar.bmel-forschung.de/receive/import_mods_00002107 |archive-date=27 September 2018 |access-date=18 April 2017 |hdl=10261/77697}}</ref> Processed food contains fewer antioxidant vitamins than fresh and uncooked foods, as preparation exposes food to heat and oxygen.<ref>{{Cite journal |vauthors=Henry CJ, Heppell N |date=February 2002 |title=Nutritional losses and gains during processing: future problems and issues |journal=The Proceedings of the Nutrition Society |volume=61 |issue=1 |pages=145–8 |doi=10.1079/PNS2001142 |pmid=12002789 |doi-access=free}}</ref>

{| class="wikitable" style="margin-left: auto; margin-right: auto;"
|-
!Antioxidant vitamins
!Foods containing high levels of antioxidant vitamins<ref name="Beecher" /><ref>{{Cite web |title=Antioxidants and Cancer Prevention: Fact Sheet |url=http://www.cancer.gov/cancertopics/factsheet/antioxidantsprevention |url-status=live |archive-url=https://web.archive.org/web/20070304120554/http://www.cancer.gov/cancertopics/factsheet/antioxidantsprevention |archive-date=4 March 2007 |access-date=27 February 2007 |publisher=National Cancer Institute}}</ref><ref>{{Cite journal |vauthors=Ortega R |date=December 2006 |title=Importance of functional foods in the Mediterranean diet |journal=Public Health Nutrition |volume=9 |issue=8A |pages=1136–40 |doi=10.1017/S1368980007668530 |pmid=17378953 |doi-access=free}}</ref>
|-
| [[Vitamin C]] (ascorbic acid)
| Fresh or frozen fruits and vegetables
|-
| [[Vitamin E]] (tocopherols, tocotrienols)
| [[Vegetable oil]]s, [[nut (fruit)|nuts]], and [[seed]]s
|-
| [[Carotenoid]]s ([[carotenes]] as [[provitamin A]])
| Fruit, vegetables and eggs
|}

Other antioxidants are not obtained from the diet, but instead are made in the body. For example, [[ubiquinol]] (coenzyme Q) is poorly absorbed from the gut and is made through the [[mevalonate pathway]].<ref name="Turunen" /> Another example is [[glutathione]], which is made from amino acids. As any glutathione in the gut is broken down to free cysteine, [[glycine]] and [[glutamic acid]] before being absorbed, even large oral intake has little effect on the concentration of glutathione in the body.<ref>{{Cite journal |vauthors=Witschi A, Reddy S, Stofer B, Lauterburg BH |year=1992 |title=The systemic availability of oral glutathione |journal=European Journal of Clinical Pharmacology |volume=43 |issue=6 |pages=667–9 |doi=10.1007/BF02284971 |pmid=1362956 |s2cid=27606314}}</ref><ref>{{Cite journal |vauthors=Flagg EW, Coates RJ, Eley JW, Jones DP, Gunter EW, Byers TE, Block GS, Greenberg RS |year=1994 |title=Dietary glutathione intake in humans and the relationship between intake and plasma total glutathione level |journal=Nutrition and Cancer |volume=21 |issue=1 |pages=33–46 |doi=10.1080/01635589409514302 |pmid=8183721}}</ref> Although large amounts of sulfur-containing amino acids such as [[acetylcysteine]] can increase glutathione,<ref name="Dodd">{{Cite journal |vauthors=Dodd S, Dean O, Copolov DL, Malhi GS, Berk M |date=December 2008 |title=N-acetylcysteine for antioxidant therapy: pharmacology and clinical utility |journal=Expert Opinion on Biological Therapy |volume=8 |issue=12 |pages=1955–62 |doi=10.1517/14728220802517901 |pmid=18990082 |s2cid=74736842}}</ref> no evidence exists that eating high levels of these glutathione precursors is beneficial for healthy adults.<ref>{{Cite journal |vauthors=van de Poll MC, Dejong CH, Soeters PB |date=June 2006 |title=Adequate range for sulfur-containing amino acids and biomarkers for their excess: lessons from enteral and parenteral nutrition |journal=The Journal of Nutrition |volume=136 |issue=6 Suppl |pages=1694S–1700S |doi=10.1093/jn/136.6.1694S |pmid=16702341 |doi-access=free}}</ref>

=== Measurement and invalidation of ORAC ===
Measurement of polyphenol and carotenoid content in food is not a straightforward process, as antioxidants collectively are a diverse group of compounds with different reactivities to various reactive oxygen species. In [[food science]] analyses in vitro, the [[oxygen radical absorbance capacity]] (ORAC) was once an industry standard for estimating antioxidant strength of whole foods, juices and food additives, mainly from the presence of [[polyphenol]]s.<ref>{{Cite journal |vauthors=Cao G, Alessio HM, Cutler RG |date=March 1993 |title=Oxygen-radical absorbance capacity assay for antioxidants |url=https://zenodo.org/record/1258621 |journal=Free Radical Biology & Medicine |volume=14 |issue=3 |pages=303–11 |doi=10.1016/0891-5849(93)90027-R |pmid=8458588}}</ref><ref>{{Cite journal |vauthors=Ou B, Hampsch-Woodill M, Prior RL |date=October 2001 |title=Development and validation of an improved oxygen radical absorbance capacity assay using fluorescein as the fluorescent probe |journal=Journal of Agricultural and Food Chemistry |volume=49 |issue=10 |pages=4619–26 |doi=10.1021/jf010586o |pmid=11599998|bibcode=2001JAFC...49.4619O }}</ref> Earlier measurements and ratings by the [[United States Department of Agriculture]] were withdrawn in 2012 as biologically irrelevant to human health, referring to an absence of physiological evidence for polyphenols having antioxidant properties ''[[in vivo]]''.<ref name="USDAx">{{Cite web |date=16 May 2012 |title=Withdrawn: Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 (2010) |url=http://www.ars.usda.gov/services/docs.htm?docid=15866 |access-date=13 June 2012 |publisher=United States Department of Agriculture, Agricultural Research Service}}</ref> Consequently, the ORAC method, derived only from ''in vitro'' experiments, is no longer considered relevant to human diets or [[biology]], as of 2010.<ref name="USDAx" />

Alternative in vitro measurements of antioxidant content in foods – also based on the presence of polyphenols – include the [[Folin-Ciocalteu reagent]], and the [[Trolox equivalent antioxidant capacity]] assay.<ref>{{Cite journal |vauthors=Prior RL, Wu X, Schaich K |date=May 2005 |title=Standardized methods for the determination of antioxidant capacity and phenolics in foods and dietary supplements |url=https://naldc.nal.usda.gov/Policy.pdf |url-status=dead |journal=Journal of Agricultural and Food Chemistry |volume=53 |issue=10 |pages=4290–302 |doi=10.1021/jf0502698 |pmid=15884874 |bibcode=2005JAFC...53.4290P |archive-url=https://web.archive.org/web/20161229203509/https://naldc.nal.usda.gov/Policy.pdf |archive-date=29 December 2016 |access-date=24 October 2017}}</ref>