The nutrition plan I give to each of my one-to-one nutritional therapy clients is unique.
However, when I am working with someone with cancer there is one group of vegetables that I nearly always recommend eating more of, and that is the crucifers.
Cruciferous vegetables are a large and diverse family, and are also called brassicas. The term “cruciferous” comes from the fact that they often have flowers that have four petals in the shape of a cross.
Varieties include:
Broccoli
Brussels sprouts
Cabbage
Cauliflower
Cavolo nero
Chinese cabbage
Horseradish
Kale
Kohlrabi
Mustard
Pak choi
Radish
Rocket
Romanesco
Spring greens
Turnip
Watercress
As you can see, there are lots to choose from, so if there’s one on the list that you’re not keen on, there are plenty of other options!
Benefits after a cancer diagnosis
Despite the difficulties involved in studying the impact of individual foods on health, there are many encouraging studies on the benefits of including cruciferous vegetables in your diet after a cancer diagnosis.
An umbrella review of over 300 high quality studies found that cruciferous vegetable intake was associated with better outcomes in gastric, lung and endometrial cancers(1).
A US study involving over 1500 men with prostate cancer found that those whose daily cruciferous vegetable intake was highest had a 59% decreased risk of progression to metastatic prostate cancer compared to those with the lowest intake(2).
A small study of 239 people with bladder cancer found that increased consumption of raw (but not cooked) cruciferous vegetables was associated with a 57% reduction in death from bladder cancer and a 43% reduction in overall mortality(3). You will understand why the study may have found a difference between raw and cooked crucifers when you read on.
The research in breast cancer is less clear. Whilst there is considerable evidence from in vitro and animal studies that specific compounds from cruciferous vegetables have activity against breast cancer, studies on the effect of eating more cruciferous vegetables on breast cancer outcomes have not shown consistent positive results(4).
Finally, higher intakes of cruciferous vegetables are associated with a reduced risk of cardiovascular disease and all-cause mortality(5). Unfortunately, cancer treatment often results in a higher risk of cardiovascular disease, and we want to reduce our risk of that too!
The compounds responsible for the benefits
Cruciferous vegetables contain sulphur; that’s what gives boiling cabbage its distinctive smell. The sulphur is present in compounds called glucosinolates. These are inactive compounds, but when the vegetables are chewed or chopped, an enzyme called myrosinase is released which converts the glucosinolates into biologically active compounds called indoles and isothiocyanates. Both of these have been extensively studied for their anticancer benefits.
Indoles
Indole-3-carbinol (I3C) is one such indole produced by glucosinolate breakdown. In the stomach, it is converted to 3,3’-diindolylmethane (DIM). It has been studied in relation to several cancers, including breast(6), prostate(7), colon(8), liver(9), and endometrial(10).
I3C and DIM have several modes of action that prevent cancer or inhibit it. The most widely known are that they beneficially alter the liver’s metabolism of oestrogen(11) and inhibit the activity of oestrogen receptors(12).
However, they have many other mechanisms of action that are not related to oestrogen, such as:
Modulation of liver detoxification enzymes(13)
Inducing apoptosis (programmed cancer cell death)(14)
Preventing cancer cells from forming their own blood supply(15)
Stopping the cell cycle (the process by which cancer cells replicate)(16)
Antioxidant and anti-inflammatory(17)
Isothiocyanates
Sulphoraphane is the isothiocyanate that is the most studied in the context of cancer. It is produced from a glucosinolate called glucoraphanin when exposed to the myrosinase enzyme. Like I3C, sulphoraphane modulates liver detoxification enzymes. Liver detoxification takes place in two phases, imaginatively named phase I and phase II. Whilst indoles affect phase I metabolism, sulphoraphane powerfully upregulates phase II metabolism, which can result in improved removal of various potentially carcinogenic chemicals from the body(18).
In addition, sulphoraphane affects cancer cell signalling and proliferation, is anti-angiogenic, antibacterial, antiviral and anti-inflammatory. It is known to affect the expression of over 200 genes, many of which protect our cells against damage(19).
An additional benefit of sulphoraphane is how it works to optimise the effects of breast cancer hormone therapy. It is common for cancer cells to eventually become resistant to hormone therapy, be it Tamoxifen, Fulvestrant, or an aromatase inhibitor. Not only does sulphoraphane make cancer cells more sensitive to treatment in the first place(20), but it can contribute to reversing acquired resistance to hormone therapy(21). A pharmaceutical form of sulphoraphane is being developed for this purpose, which was shown in a trial to reverse resistance in 26% of women with stage 4 breast cancer who had previously become resistant to hormone therapy(22). It can take a long time before a trial drug is actually available to patients, but of course there is nothing stopping you from obtaining plenty of sulphoraphane in its natural form from cruciferous vegetables.
Maximising the nutrient content of crucifers
Firstly, remember that in order for indoles and isothiocyanates to be produced, the myrosinase enzyme needs to act on the glucosinolates in cruciferous vegetables. Myrosinase needs time to act, and if cruciferous vegetables are cooked before this has happened, the sulphoraphane content is considerably reduced(23). If you can, chop your cruciferous vegetables at least 40 minutes and up to 90 minutes before you cook them. Sometimes this is not practical, but do what you can. Alternatively, sprinkling some powdered mustard seed over your cooked cruciferous vegetables before eating has been shown to increase their available sulphoraphane, because mustard seeds contain myrosinase(24).
Cooking methods also make a difference. Boiling leads to a loss of sulforaphane because glucosinolates leach into the cooking water, while steaming and stir-frying retain more sulforaphane(25, 26).
Finally, you may wish to consider growing and eating broccoli sprouts. Broccoli sprouts are the first shoots that appear when you begin to grow broccoli from seed. With watering, they only take 3-4 days to grow. The remarkable thing about broccoli sprouts is that they contain 10-100 times as much sulphoraphane as the same weight of a mature broccoli plant(27)! Sprouting broccoli seeds is easy and very cheap. Make sure you choose broccoli calabrese seeds and not broccoli raab. I use a multi-tiered sprouting tray to spread the seeds on but you can also sprout seeds in a jar. I place the tray on a windowsill and rinse the seeds in water at least twice a day. They sprout faster in warmer than in colder weather, but usually they are ready to eat, with peak glucosinolate content, in 3-4 days. Broccoli sprouts have a pleasant peppery taste and are good sprinkled on top of salads. Remember that you need to chew them well so that the glucosinolates get converted to sulphoraphane.
Enjoy your crucifers!
References
1. Li, Y.-Z., Yang, Z.-Y., Gong, T.-T. et al. (2022). ‘Cruciferous vegetable consumption and multiple health outcomes: an umbrella review of 41 systematic reviews and meta-analyses of 303 observational studies’, Food & Function, 13(8), pp4247-4259. Available at https://pubmed.ncbi.nlm.nih.gov/35352732/ (Accessed 25 July 2023).
2. Richman, E.L., Carroll, P.R. and Chan, J.M. (2012). ‘Vegetable and fruit intake after diagnosis and risk of prostate cancer progression’, International Journal of Cancer, 131(1), pp201-210. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3310254/ (Accessed 25 July 2023).
3. Tang, L., Zirpoli, G.R., Guru, K. et al. (2010). ‘Intake of Cruciferous Vegetables Modifies Bladder Cancer Survival’, Cancer Epidemiology, Biomarkers & Prevention, 19(7), pp1806-1811. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2901397/ (Accessed 25 July 2023).
4. Ngo, S.N.T. and Williams, D.B. (2021). ‘Protective Effect of Isothiocyanates from Cruciferous Vegetables on Breast Cancer: Epidemiological and Preclinical Perspectives’, Anti-cancer Agents in Medicinal Chemistry, 21(11), pp1413-1430. Available at https://pubmed.ncbi.nlm.nih.gov/32972351/ (Accessed 25 July 2023).
5. Aune, D., Giovannucci, E., Boffetta, P. et al. (2017). ‘Fruit and vegetable intake and the risk of cardiovascular disease, total cancer and all-cause mortality—a systematic review and dose-response meta-analysis of prospective studies’, International Journal of Epidemiology, 46(3), pp1029-1056. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5837313/ (Accessed 25 July 2023).
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14. Howells, L.M., Gallacher-Horley, B., Houghton, C.E. et al. (2002). ‘Indole-3-carbinol Inhibits Protein Kinase B/Akt and Induces Apoptosis in the Human Breast Tumor Cell Line MDA MB468 but not in the Nontumorigenic HBL100 Line’, Molecular Cancer Therapeutics, 1(13), pp1161-1172. Available at http://mct.aacrjournals.org/content/1/13/1161.long (Accessed 24 July 2023).
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16. Cover, C.M., Hsieh, S.J., Tran, S.H. et al. (1998). ‘Indole-3-carbinol Inhibits the Expression of Cyclin-dependent Kinase-6 and Induces a G1 Cell Cycle Arrest of Human Breast Cancer Cells Independent of Estrogen Receptor Signaling’, The Journal of Biological Chemistry, 273(7), pp3838-3847. Available at http://www.jbc.org/content/273/7/3838.full (Accessed 24 July 2023).
17. Fuentes, F., Paredes-Gonzalez, X and Kong, A.T. (2015). ‘Dietary Glucosinolates Sulforaphane, Phenethyl Isothiocyanate, Indole-3-Carbinol/3,3′-Diindolylmethane: Anti-Oxidative Stress/Inflammation, Nrf2, Epigenetics/Epigenomics and In Vivo Cancer Chemopreventive Efficacy’, Current Pharmacology Reports, 1(3), pp179-196. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4596548/ (Accessed 24 July 2023).
18. Fahey, J.W. and Talalay, P. (1999). ‘Antioxidant Functions of Sulforaphane: a Potent Inducer of Phase II Detoxication Enzymes’, Food and Chemical Toxicology, 37, pp973-979. Available at https://www.sciencedirect.com/science/article/pii/S0278691599000824?via%3Dihub (Accessed 1 August 2023).
19. Tortorella, S.M., Royce, S. G., Licciardi, P.V et al. (2015). ‘Dietary Sulforaphane in Cancer Chemoprevention: The Role of Epigenetic Regulation and HDAC Inhibition’, Antioxidants & Redox Signalling, 2(16), pp1382-1424. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4432495/ (Accessed 1 August 2023).
20. Pawlik, A., Slominska-Wojewodzka, M. and Herman-Antosiewicz, A. (2016). ‘Sensitization of estrogen receptor-positive breast cancer cell lines to 4-hydroxytamoxifen by isothiocyanates present in cruciferous plants’, European Journal of Nutrition, 55, pp1165-1180. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4819954/ (Accessed 1 August 2023).
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23. Wu. Y., Shen, Y., Wu, X. et al. (2018). ‘Hydrolysis before Stir-Frying Increases the Isothiocyanate Content of Broccoli’, Journal of Agriculture and Food Chemistry, 66(6), pp1509-1515. Available at https://pubs.acs.org/doi/abs/10.1021/acs.jafc.7b05913 (Accessed 1 August 2023).
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