Phytochemicals are natural compounds found in plants that are responsible for the colour, taste and aroma of foods.
As well as these pleasant attributes, they protect us from environmental and ingested carcinogens by arming antioxidant enzymes and enhancing DNA repair pathways. They also have direct effects on the fundamental hallmarks of cancer progression and metastasis.
It is not a surprise then that the World Cancer Research Fund and other academic bodies report that individuals eating phytochemical-rich foods have a lower risk of cancer or relapse after treatments.
What foods are high in phytochemicals?
There is a wide range of dietary phytochemicals, but one of the largest well-known groups are the polyphenols. The average total dietary intake of polyphenols is reported to be over 1g per day, which is up to ten times higher than that of all other classes of phytochemicals and known dietary antioxidants.1
There are three major groups of phytochemicals:
1. Polyphenols – subcategorised as the flavonoids, phenolic acids and other non-flavonoid polyphenols
- Flavonols: quercetin, kaempferol (onions, kale, leeks, broccoli, buckwheat, red grapes, tea, apples)
- Flavones: apigenin, luteolin (celery, herbs, parsley, chamomile, rooibos tea, capsicum pepper)
- Isoflavones: genistein, daidzein, glycitein (soya, beans, chick peas, alfalfa, peanuts)
- Flavanones: naringenin, hesperitin (citrus fruit)
- Anthocyanidins (red grapes, blueberries, cherries, strawberries, blackberries, raspberries, tea)
- Flavan-3-ols (tannins): catechins, epicatechin, epigallocatechin gallate (tea, chocolate, grapes)
- Flavanolols: silymarin, silibinin, aromadedrin (milk thistle, red onions)
- Dihydrochalcones: phloridzin, aspalathin (apples, rooibos tea)
- Hydrobenzoic acids: gallic acid, ellagic acid, vanillic acid (rhubarb, grape seed, raspberries, blackberries, pomegranate, vanilla, tea)
- Hydroxycinnamic acids: ferulic acid, P-coumaric acid, caffeic acid, sinapic acid (wheat bran, cinnamon, coffee, kiwi fruit, plums, blueberries)
Other non-flavonoid polyphenols:
- Other tannins (cereals, fruits, berries, beans, nuts, wine, cocoa)
- Curcuminoids: curcumin (turmeric)
- Stilbenes: cinnamic acid, resveratrol (grapes, wine, blueberries, peanuts, raspberries)
- Lignans: secoisolariciresinol, enterolactone, sesamin (grains, flaxseed, sesame seeds)
2. Terpenoids – subcategorised as the carotenoids and non-carotenoid terpenoids
- Alpha, beta and gamma carotene (sweet potato, carrots, pumpkin, kale)
- Lutein (corn, eggs, kale, spinach, red pepper, pumpkin, oranges, rhubarb, plum, mango, papaya)
- Zeaxanthin (corn, eggs, kale, spinach, red pepper, pumpkin, oranges)
- Lycopene (tomatoes watermelon, pink grapefruit, guava, papaya)
- Astaxanthin (salmon, shrimp, krill, crab)
- Saponins (chickpeas, soya beans)
- Limonene (the rind of citrus fruits)
- Perillyl Alcohol (cherries, caraway seeds, mint)
- Phytosterols: natural cholesterols, siosterol, stigmasterol, campesterol (vegetable oils, cereal grains, nuts, shoots, seeds and their oils, whole grains, legumes)
- Ursolic acid (apples, cranberries, prunes, peppermint, oregano, thyme)
- Ginkgolide and bilobalide (Ginkgo biloba)
3. Thiols – includes the glucosinolates, allylic sulfides and non-sulfur containing indoles
- Isothiocyanates (sulforaphane) and dithiolthiones (cruciferous vegetables such as broccoli, asparagus, Brussels sprouts, cauliflower, horseradish, radish and mustard)
- Allicin and S-allyl cysteine (garlic, leeks, onions)
- Indole-3-carbinol (broccoli, Brussels sprouts)
Other phytochemical groups, which although have some properties within these groups, have been classified within a miscellaneous category, including:
- Betaines (beetroot)
- Chlorophylls (green leafy vegetables)
- Capsaicin (chilli)
- Peperine (black peppers)
Why are phytochemicals important?
The health benefits of phytochemical-rich foods or concentrated nutritional supplements are often being highlighted in the medical and popular media, and hence they are an increasing topic of conversation between medical practitioners and their patients, especially those with cancer who have a particular interest in over-the-counter self-help strategies2,3.
There is increasingly convincing evidence to show that plant phytochemicals, particularly polyphenols, have significant benefits for humans, such as reducing our risk of cancer and helping people living with and beyond treatments.
Living well programmes, slowly being introduced in the UK, are beginning to highlight the importance of phytochemical-rich diets, as well as other lifestyle factors, largely being driving by the National Survivorship Initiative and guidelines from influential organisations such as the American Society of Clinical Oncology (ASCO).
Going a step further and concentrating these foods, or extracted elements of these foods, into nutritional supplements gives an opportunity to boost their beneficial anti-cancer effects, but have their pitfalls. Studies of concentrated minerals, vitamins and phytoestrogenic supplements have reported detrimental effects. No study has reported detrimental effects of whole, non-phytoestrogenic food supplements and some have reported significant advantages.
Despite these potential benefits and reports that over 60% of patients living with and beyond cancer take nutritional supplements, oncologists have been reluctant to discuss their pros and cons due to a lack of randomised controlled trials from academic institutions4,5. Hopefully this trend will change, particularly following the success of the Pomi-T study6 and ongoing studies registered with the National Cancer Institute.
- Scalbert A, Johnson I and Satlmarsh M. Polyphenols: antioxidants and beyond. American Journal of Clinical Nutrition 2005;81(1): 215S-217S.
- Bauer CM, Johnson EK, Beebe-Dimmer JL, et al. Prevalence and correlates of vitamin and supplement usage among men with a family history of prostate cancer. Integrative Cancer Therapies 2012;11(2): 83-89.
- Uzzo RG, Brown JG, Horwitz EM, et al. Prevalence and patterns of self-initiated nutritional supplementation in men at high risk of prostate cancer. British Journal of Urology International 2004;93(7): 955-960.
- Voorrips LE1, Goldbohm RA, van Poppel G, et al. Vegetable and fruit consumption and risks of colon and rectal cancer in a prospective cohort study: The Netherlands Cohort Study on Diet and Cancer. American Journal of Epidemiology 2000 Dec 1;152(11): 1081-92.
- Liao J, yang GY, Park ES (2004). Inhibition of lung carcinogenesis and effects on angiogenesis and apoptosis in mice given green tea. Nutrition and Cancer 2004;48(1): 44-53.
- Thomas R, Williams M, Bellamy P, et al. A double blind, placebo controlled randomised trial (RCT) evaluating the effect of a polyphenol rich whole food supplement on PSA progression in men with prostate cancer – The UK National Cancer Research Network (NCRN) Pomi-T study. Prostate Cancer and Prostatic Diseases 2014;17: 180–186.