Before we start looking at the research, let me first explain what phyto-oestrogens are and how they work.These plant chemicals are naturally-occurring forms of the female hormone oestrogen that are found in certain foods, specifically soya products such as soya milk, tofu, tempeh and miso, plus pulses, linseeds and a variety of vegetables. The action they have in the body is that of a weak oestrogen because they bind to hormone receptors. But they are also adaptogens, which means that they help to reduce high levels of oestrogen or boost low levels.
They have an important role in helping to regulate hormones and can be used to relieve the unpleasant effects of the menopause (flushing, night sweats etc), which I’ve talked about in other reports on this site. What most scientists agree on is that including dietary sources of phyto-oestrogens reduces your risk of developing cancer. For example, we know that Asians who consume a phyto-oestrogen-rich diet have much lower rates of breast, prostate and colon cancer than we do in the UK, elsewhere in Europe or the US.
Where the real divisions arise, however, is whether phyto-oestrogens are safe to consume if you actually have cancer. Yes or no really depends on what you read and how you analyse the data. “There have been no properly-run human studies which show that phytoestrogens make cancer grow,” says Dr Margaret Ritchie, an expert in phyto-oestrogens from the Bute Medical School at the University of St Andrews. Indeed there are plenty that show the opposite. For example, a study published in the Lancet compared 144 women newly diagnosed with breast cancer with 144 controls (ie women without breast cancer) and assessed risk compared to phyto-oestrogen intake. Researchers concluded: “There is a substantial reduction in breast-cancer risk among women with a high intake (as measured by excretion) of phyto-oestrogens.”
A recent review of the evidence by the Committee on Toxicology (COT), part of the UK’s Food Standards Agency, also found largely in favour of phyto-oestrogens use for breast cancer. According to the draft report of the COT Working Group on Phyto-oestrogens: “Most epidemiological studies… have reported an inverse association between soy consumption and breast cancer.” In other words, the majority of research into the effects of one of the richest sources of phyto-oestrogens, soy, shows it reduces breast cancer.
In studies on prostate cancer, the COT report quoted a American study involving more than 12,000 men (Jacobsen et al, 1998) which showed that frequent consumption (ie more than once a day) of soya milk was associated with a 70 per cent reduction in prostate cancer risk. Where the research is more divided is where phytoestrogens are tested on animals, in particular rats. But as Dr Ritchie explained to me, this is because rats handle phytoestrogens in a different way to humans. For a start, rats naturally excrete a very potent natural phyto-oestrogen called equol, and this means they process dietary phyto-oestrogens differently. Only around 30 per cent of humans excrete equol, and not in equivalent concentrations, so already we can see why we’re not comparing like with like.
Also, many rat studies inject their subjects with phyto-oestrogens, so bypassing the digestive tract. In real life, we consume them and our gut flora breaks them down into different chemical compounds before they are absorbed in the blood, so what we end up with is often different.
How to boost phyto-oestrogens in your diet
There are many types of phyto-oestrogens – more than 800 in total. One of the most potent forms, used in a lot of the cancer research, is called isoflavones – in particular compounds called genistein and daidzein – and these are found in highest concentrations in soya products. Others called liganans are found in linseeds, black/green tea, coffee, fruits and vegetables, split peas, lentils and beans. And another common category called coumestans is found in alfalfa, beans, split peas and lentils.
To help people understand how to boost levels of phytoestrogens in their diet, Dr Margaret Ritchie has spent the past three years measuring levels of the isoflavone family of phyto-oestrogens in commonly eaten foods. She’s created a database that’s a world first as it assesses levels based not only on the actual food content, but that are also corroborated with what’s absorbed and excreted after human consumption. “Put simply, we’re pinpointing foods which you can introduce to your diet – or that of your teenage son or daughter – so they can build up cancer protection in later life,” Dr Ritchie told me. For the best results, she recommends having some phytoestrogen-rich foods at least once a day, as blood levels of the beneficial compounds they contain start to decline six hours after eating. “Asians eat small quantities of soya and other plant-based foods regularly throughout the day and this seems to be the most beneficial,” she says.
Based on her research, I recommend you aim for around 15mg (15,000mcg) of phyto-oestrogens a day. This is easily achieved by having a small portion of tofu (100g serving provides 78mg), or a 100mg glass of soya milk or soya yoghurt (11mg) and a portion of chickpeas, perhaps as hummous (2mg). Eating rye bread, beansprouts, beans, lentils, nuts and seeds also helps boost your levels – these are the very foods that are staples in the East and unheard of by many in the West. The phyto-oestrogen database has already been used in the University of Edinburgh’s prostate cancer study and will be used in Scotland’s largest breast cancer study undertaken by the University of Aberdeen, which will specifically look at young women who tend to develop the most aggressive strain of the disease.
Phytoestrogen Content Of Commonly-eaten Foods MCG Per 100g
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