These otherwise referred to as “Phytoestrogens” which include flavones, isoflavones, flavanones (genistein, daidzein, glycitein and equaol) derived, in human diet, mainly from soybeans. The other type - Lignans (mainly enterolactone) are derived mainly from legumes, including peas, lentils and beans.

The phytoestrogens and cancer story remains one of the most controversial and disputed subjects among cancer doctors. Many of whom, remain undecided whether they are harmful or beneficial after a diagnosis of cancer particularly originating from the breast. Historically, the implication of benefit stems from the finding that populations and cultures that have had a high dietary intake of phytoestrogenic foods such as those from the far east have the lowest incidence of cancer and indeed menopausal symptoms such as hot flushes, and osteoporosis. The positive effect on cancer is thought to arise via their affinity to the oestrogen receptor in breast or uterine tissues and for that matter cancer cells that originate from them. They attach to the receptor but only have weak oestrogenic activity. This means the very much stronger own body’s oestrogen has less influence on the receptor i.e. they dilute the effect of their own body’s oestrogen. Furthermore, studies on genestein have shown that it attaches to the oestrogen receptor in the same way as tamoxifen – inhibiting the oestrogen effect on tumours but stimulating the bones and uterus.

This sounds ideal but evidence is rather cloudy. The anti-cancer benefit may simply be via the antioxidant effect of the healthier food rather that the oestrogenic action and some suggest there may be other factors in the East which are beneficial so simply taking soya products may not translate into a western diet. Furthermore, just because they may reduce the incidence of cancer developing originally, this does not necessary mean they would reduce the severity once breast cancer has established. On a concerning note, animal studies have also shown that phytoestrogens supplements are capable of stimulating tumour cell growth as well as having effects on the bodies normal cells sensitive to oestrogen such as breast and uterine tissues so they may not be that innocent after all.

A placebo controlled study looking at the cancer (good or bad) effects in humans has not been performed (and it would take a very brave team to do one!). There have however been trials of phytoestrogen supplements among patients with breast cancer looking at whether they could reduce their hot flushes and so far they have not shown an increased risk of cancer. As these trials had not set out to examine the cancer effect, in mathematical terms they were not designed to have the statistical power to be comforted by these findings. Interesting and probably of more relevance, none of the trials of phytoeostrenic supplementation actually showed a difference in the main end point – hot flushes. Protagonist against phytoestrogens, therefore have a fair point when they argue that the supplement used in these studies could either have not been powerful enough or patients had not taken at a high enough dose to help their hot flushes. So, they argue, if the supplement had been active against hot flushes they would have more likely risked the stimulation of occult residual cancer cells stimulating relapse. In other worlds, for hot flushes, if phytoestrogens work they could be harmful, if they don’t there is no point taking them anyway! 

With conflicting circumstantial evidence on phytoestrogens, most oncologist agree that it would be unwise to take phytoestrogen supplements particularly in patients with breast cancer. Most agreed that foods containing phytoestrogens such as soya legumes are generally healthy and have lots of antioxidants, essential trace elements, fibre, healthy fats and vitamins and should not be discouraged. A large dietary and lifestyle study, currently underway in the UK may help solve this dilemma. The DietCompLfy study is looking at women who have been successfully treated with breast cancer and over the following years they measure levels of phytoestrogens in their blood stream as well as take a detailed dietary history. It will then compare the phytoestrogen exposure between those who have relapsed with those who have survived.

As regards prostate cancer, dietary phytoestrogen intake could potentially create a more favourable hormonal milieu for cancer cells to stop growing. Oestrogenic chemicals have been shown to inhibit 5 alph-reductase, the enzyme responsible for converting testosterone to the more active metabolite dihydrotestosterone, which is responsible for stimulating prostate cancer cells. Numerous supplements are available over the internet containing phytoestrogens some combined with antioxidants. The most notable of these, which was tested in a clinical trial was called PC-SPEC, a commercially available mixture supposedly of eight herbs. The trial did demonstrating PSA reduction in some patients. On detailed analysis however, the supplement was later found to contain contaminants of an actual drugs including diethylstilboestrol, indomethacin and warfarin. The Food and Drug administration therefore advised patients against it and subsequently it has been withdrawn from the market by the manufacturer.  The general view of oncologist on supplements for prostate cancer is that once foods are formulated into tabled they become chemicals and should be tested formally and the concentrating them may, despite their anti-male hormone effect, may be detrimental.

Further general information Your doctors and specialist nurses are in an ideal position to give you relevant information on your disease and treatment as they know your individual circumstances. Cancerbackup has a help line (0808 800 1234) and a prize winning video available in English, Italian, Urdu, Bengali, Gujarati & Hindi explaining Radiotherapy & Chemotherapy. Cancernet.co.uk has over 500 pages describing cancer, its management, practical tips and tool which patients, their carers and their doctors have found helpful during the cancer journey.