Phytochemicals are naturally occurring chemicals present in orextracted fromplants.[1][2] Some phytochemicals arenutrients for the plant, while others aremetabolites produced to enhance plant survivability and reproduction.[3]
The fields of extracting phytochemicals for manufactured products or applying scientific methods to study phytochemical properties are calledphytochemistry.[2][3] An individual who uses phytochemicals infood chemistry manufacturing or research is aphytochemist.
The term phytochemical does not generally imply that there is any biological activity or health benefit following its consumption.[2] Once phytochemicals in a food enter thedigestion process, the fate of individual phytochemicals in the body is unknown due to extensivemetabolism of the food in thegastrointestinal tract, producing phytochemical metabolites with different biological properties from those of the parent compound that may have been testedin vitro.[4] Further, thebioavailability of many phytochemical metabolites appears to be low, as they are rapidlyexcreted from the body within minutes.[4] Other than fordietary fiber, no non-nutrient phytochemicals have sufficient scientific evidence for providing ahealth benefit.
Phytochemicals are chemicals produced by plants throughprimary orsecondary metabolism.[2][6] They generally havebiological activity in the plant host and play a role in plant growth or defense against competitors, pathogens, or predators.[7] As components of plants, all individual phytochemicals make up the whole plant as it exists innature.[2][8]
Phytochemists study phytochemicals by first extracting and isolating compounds from the origin plant, followed by defining their structure or testing in laboratory model systems, such as in vitro studies orin vivo studies usinglaboratory animals.[2][7] Challenges in that field include isolating specific compounds and determining their structures, which are often complex, and identifying what specific phytochemical is primarily responsible for any given biological activity.[2][7]
Further, upon consuming phytochemicals in a food entering the digestion process, the fate of individual phytochemicals in the body is unknown due to extensive metabolism in the gastrointestinal tract, producing smaller phytochemical metabolites with different biological properties from those of the parent compound, and with low bioavailability and rapid excretion.[4] Other than for dietary fiber,[13] no non-nutrient phytochemical has sufficient scientific evidence in humans for an approved health claim.[14]
TheEnglish yew tree was long known to be extremely and immediately toxic to animals that grazed on its leaves or children who ate its berries; however, in 1971,paclitaxel was isolated from it, subsequently becoming acancer drug.[7]
The biological activities for most phytochemicals are unknown or poorly understood, in isolation or as part of foods.[2][7][9] Phytochemicals with established roles in the body are classified asessential nutrients.[1][2]
The phytochemical category includes compounds recognized as essential nutrients, which are naturally contained in plants and are required for normalphysiological functions, so must be obtained from thediet in humans.[2]
Some phytochemicals are knownphytotoxins that are toxic to humans;[20][21] for examplearistolochic acid is carcinogenic at low doses.[22] Some phytochemicals areantinutrients that interfere with the absorption of nutrients.[23] Others, such as some polyphenols and flavonoids, may bepro-oxidants in high ingested amounts.[24]
Phytochemicaldietary supplements are neither recommended by health authorities for improving health[9][27] nor are they approved by regulatory agencies for health claims on product labels.[14][28]
While health authorities encourage consumers to eat diets rich in fruit, vegetables,whole grains,legumes, and nuts to improve and maintain health, evidence that such effects result from specific, non-nutrient phytochemicals is limited or absent.[1][2] For example,systematic reviews and/ormeta-analyses indicate weak or no evidence for phytochemicals from plant food consumption having an effect onbreast,lung, orbladder cancers.[29][30] Further, in the United States, regulations exist to limit the language on product labels for how plant food consumption may affect cancers, excluding mention of any phytochemical except for those with established health benefits against cancer, such asdietary fiber,vitamin A, andvitamin C.[31]
Phytochemicals, such as polyphenols, have been specifically discouraged from food labeling in Europe and the United States because there is no evidence for acause-and-effect relationship between dietary polyphenols and inhibition or prevention of any disease.[14][32]
Among carotenoids such as thetomato phytochemical,lycopene, the USFood and Drug Administration found insufficient evidence for its effects on any of several cancer types, resulting in limited language for how products containing lycopene can be described on labels.[33]
Phytochemicals in freshly harvested plant foods may be degraded by processing techniques, including cooking.[34] The main cause of phytochemical loss from cooking isthermal decomposition.[34]
A converse exists in the case of carotenoids, such as lycopene present intomatoes, which may remain stable or increase in content from cooking due to liberation from cellular membranes in the cooked food.[35]Food processing techniques like mechanical processing can also free carotenoids and other phytochemicals from the food matrix, increasing dietary intake.[34][36]
In some cases, processing of food is necessary to remove phytotoxins or antinutrients; for example societies that usecassava as a staple have traditional practices that involve some processing (soaking, cooking,fermentation), which are necessary to avoid illness fromcyanogenic glycosides present in unprocessed cassava.[37]
^abcde"Flavonoids". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis, Oregon. February 2016. Retrieved9 April 2025.
^Harborne JB, Baxter H, Moss GP, eds. (1999)."General Introduction".Phytochemical dictionary a handbook of bioactive compounds from plants (2nd ed.). London: Taylor & Francis. p. vii.ISBN978-0-203-48375-6.
^"Carotenoids". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis, Oregon. October 2023. Retrieved9 April 2025.
^Dewanto V, Wu X, Adom KK, et al. (2002). "Thermal processing enhances the nutritional value of tomatoes by increasing total antioxidant activity".Journal of Agricultural and Food Chemistry.50 (10):3010–4.Bibcode:2002JAFC...50.3010D.doi:10.1021/jf0115589.PMID11982434.
Higdon, J.An Evidence – Based Approach to Dietary Phytochemicals. 2007. Thieme.ISBN978-1-58890-408-9.
Rosa, L.A. de la / Alvarez-Parrilla, E. / González-Aguilar, G.A. (eds.)Fruit and Vegetable Phytochemicals: Chemistry, Nutritional Value and Stability. 2010. Wiley-Blackwell.ISBN978-0-8138-0320-3.
Media related toPhytochemicals at Wikimedia Commons