Phytochemicals are
chemical compounds produced by
plants, generally to help them resist fungi, bacteria and
plant virus infections, and also consumption by insects and other animals. The name comes from
Greekφυτόν (phyton) 'plant'. Some phytochemicals have been used as
poisons and others as
traditional medicine.
As a term, phytochemicals is generally used to describe plant compounds that are under research with unestablished effects on health, and are not
essential nutrients. Regulatory agencies governing food labeling in Europe and the United States have provided guidance for industry to limit or prevent
health claims about phytochemicals on food
product or nutrition labels.
Definition
Phytochemicals are chemicals of
plant origin.[1] Phytochemicals (from Greek phyto, meaning "plant") are chemicals produced by plants through primary or secondary
metabolism.[2][3] They generally have
biological activity in the plant host and play a role in plant growth or defense against competitors, pathogens, or predators.[2]
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 using
cell lines or in vivo studies using
laboratory animals.[2] 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][10][11]
The
English 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 an important
cancer drug.[2]
As of 2017[update], the biological activities for most phytochemicals are unknown or poorly understood, in isolation or as part of foods.[2][5] Phytochemicals with established roles in the body are classified as
essential nutrients.[4][17]
Functions
The phytochemical category includes compounds recognized as essential nutrients, which are naturally contained in plants and are required for normal
physiological functions, so must be obtained from the
diet in humans.[17][18]
Some phytochemicals are known
phytotoxins that are toxic to humans;[19][20] for example
aristolochic acid is carcinogenic at low doses.[21] Some phytochemicals are
antinutrients that interfere with the absorption of nutrients.[22] Others, such as some polyphenols and flavonoids, may be
pro-oxidants in high ingested amounts.[23]
Eating a diet high in fruits, vegetables, grains, legumes and plant-based beverages has long-term health benefits,[17] but there is no evidence that taking
dietary supplements of non-nutrient phytochemicals extracted from plants similarly benefits health.[4] Phytochemical supplements are neither recommended by health authorities for improving health[5][27] nor approved by regulatory agencies for health claims on product labels.[28][29]
Consumer and industry guidance
While health authorities encourage consumers to eat diets rich in fruit, vegetables,
whole grains,
legumes, and nuts to improve and maintain health,[17] evidence that such effects result from specific, non-nutrient phytochemicals is limited or absent.[4] For example,
systematic reviews and/or
meta-analyses indicate weak or no evidence for phytochemicals from plant food consumption having an effect on
breast,
lung, or
bladder cancers.[30][31] 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 as
dietary fiber,
vitamin A, and
vitamin C.[32]
Phytochemicals, such as polyphenols, have been specifically discouraged from food labeling in Europe and the United States because there is no evidence for a
cause-and-effect relationship between dietary polyphenols and inhibition or prevention of any disease.[28][33]
Among carotenoids such as the
tomato phytochemical,
lycopene, the US
Food 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.[34]
Effects of food processing
Phytochemicals in freshly harvested plant foods may be degraded by processing techniques, including cooking.[35] The main cause of phytochemical loss from cooking is
thermal decomposition.[35]
A converse exists in the case of
carotenoids, such as
lycopene present in
tomatoes, which may remain stable or increase in content from cooking due to liberation from cellular membranes in the cooked food.[36]Food processing techniques like mechanical processing can also free carotenoids and other phytochemicals from the food matrix, increasing dietary intake.[35][37]
In some cases, processing of food is necessary to remove phytotoxins or antinutrients; for example societies that use
cassava as a staple have traditional practices that involve some processing (soaking, cooking, fermentation, etc.), which are necessary to avoid getting sick from
cyanogenic glycosides present in unprocessed cassava.[38]
^Harborne, Jeffrey B.; Baxter, Herbert; Moss, Gerard P., eds. (1999).
"General Introduction". Phytochemical dictionary a handbook of bioactive compounds from plants (2nd ed.). London: Taylor & Francis. p. vii.
ISBN9780203483756.
^
abcd"Phytochemicals". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis, Oregon. 2017. Retrieved 12 February 2017.
^"Carotenoids". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis, Oregon. July 2016. Retrieved 12 February 2017.
^
ab"Flavonoids". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis, Oregon. November 2015. Retrieved 12 February 2017.
^"Fiber". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis, Oregon. April 2012. Retrieved 12 February 2017.
^Smith-Warner, S. A.; Spiegelman, D; Yaun, S. S.; Albanes, D; Beeson, W. L.; Van Den Brandt, P. A.; Feskanich, D; Folsom, A. R.; Fraser, G. E.; Freudenheim, J. L.; Giovannucci, E; Goldbohm, R. A.; Graham, S; Kushi, L. H.; Miller, A. B.; Pietinen, P; Rohan, T. E.; Speizer, F. E.; Willett, W. C.; Hunter, D. J. (2003).
"Fruits, vegetables and lung cancer: A pooled analysis of cohort studies". International Journal of Cancer. 107 (6): 1001–11.
doi:10.1002/ijc.11490.
PMID14601062.
S2CID28381529.
^
abcPalermo, M; Pellegrini, N; Fogliano, V (2014). "The effect of cooking on the phytochemical content of vegetables". Journal of the Science of Food and Agriculture. 94 (6): 1057–70.
doi:
10.1002/jsfa.6478.
hdl:11381/2677278.
PMID24227349.
^Dewanto, V; Wu, X; Adom, KK; Liu, RH (2002). "Thermal processing enhances the nutritional value of tomatoes by increasing total antioxidant activity". Journal of Agricultural and Food Chemistry. 50 (10): 3010–4.
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.