Here we’re looking specifically at phytochemicals – ‘phyto’ meaning ‘of, or relating to plants’ – so chemicals from plants.
Phytochemicals are found in fruits, vegetables and plant derivatives such as tea, coffee, cocoa and wine – see Table 1 below. In plants, the colour, flavour and smell of these compounds are often present to detract pests. As a food source and part of a healthy diet they provide recognised health benefits.
Table 1: Examples of phytochemicals and their sources
| Phytochemical | Sub group | Source |
|---|---|---|
| Polyphenol | Isoflavone | Soybeans and other legumes |
| Polyphenol | Flavanone | Citrus fruits, e.g. lemons, oranges, grapefruits |
| Polyphenol | Flavone | Herbs, e.g. parsley and thyme, also celery, garlic, green peppers |
| Polyphenol | Flavonol | Onions, broccoli, apples, tea, grapes and grape products, e.g. juice and wine |
| Polyphenol | Flavanol | Apples, pears, legumes, grapes and grape products, e.g. juice and wine, also cocoa and tea |
| Polyphenol | Anthocyanin | Red, blue, purple foods, e.g. aubergine skin, blackberries, blackcurrants, blueberries, grapes and grape products, e.g. juice and wine |
| Carotenoid | Xanthophyll | Yellow/orange/red foods, e.g. papaya, squash, pumpkin, sweet potato, also spinach, kale |
| Carotenoid | Carotene (can be converted to Vitamin A) | Carrots, broccoli, asparagus, apricots |
The flavonoids mostly found in a western diet are flavanone, flavone, flavonol, flavanol and anthocyanin. Flavonoid bioavailability is low due to poor absorption in the small intestine; their metabolites are readily excreted, consequently they have no dietary reference intake values. However numerous studies have reported their positive effect in lowering raised blood pressure as well as their efficacy in risk reduction for chronic conditions such as cardiovascular disease and type 2 diabetes1.
Despite their vitamin like qualities, the carotenoids similarly have no dietary reference intake values. The xanthophylls are mainly associated with eye health and more specifically the health of the retina. They can protect against late age-related macular degeneration (AMD), a leading cause of blindness in the elderly2
Of the carotenes, beta-carotene is the most studied. Dietary beta-carotene is regarded as a powerful antioxidant, meaning it can help reduce the damage to tissues and cells caused by free-radicals.
References
- Clark, J.L., Zahradka, P., Taylor, C.G. Efficacy of flavonoids in the management of high blood pressure. Nutrition Reviews [Online]. Oxford Academic. December 2015, vol. 73 (12), pp 799-822 [viewed 16 March 2021]. Available from https://doi.org/10.1093/nutrit/nuv048
- Le, M. et al. Lutein and zeaxanthin intake and the risk of age-related macular degeneration: a systematic review and meta-analysis. British Journal of Nutrition [Online]. Cambridge University Press. September 2011, vol. 107 (3), pp 350-359 [viewed 16 March 2021]. Available from DOI:10.1017/S0007114511004260
