Straight Talk about Soy


Soy. Apparently it causes breast cancer. But some say it protects against breast cancer. Oh but have you heard it makes men grow boobs? Or that it might reduce thyroid function? What about it's full of chemicals. But then don't worry, it's natural. Confused? Let's get the facts straight about this very misunderstood plant.

Soy has always been a traditional part of the Asian diet and popularity has now increased in Western Countries as we recognise East Asian countries have lower incidences of heart disease and cancers. 

A wide variety of soy products, made from the soy (or soya) bean plant are now readily available on our supermarket shelves. Un-fermented products like soya milk, tofu, edamame (green, immature) beans and nuts tend to be more popular in the UK than fermented products like miso, soy sauces and tempeh.

Then there's the second generation of soy products including tofu burgers, 'chicken' strips and sausages. If you've ever tried scheese you'll know it's really nothing like cheese but 10/10 for effort.

So what's in soy that some people are so worried about?

Nutritionally speaking, it’s great! The soybean is rich in high quality protein, fat, fibre, Magnesium, Potassium, Calcium, Iron, B vitamins and Vitamin K. 

Soy also contains plant (phyto)chemicals that include anti-nutrients (that block nutrient absorption), sterols and isoflavones which have received much interest regarding their potential influence on health.

Isoflavones have powerful anti-oxidant properties and are a type of phytoestrogen. This is because they are structurally similar to oestradiol, the main oestrogen in men and premenopausal women. Phytoestrogens mimic the body's own oestrogen but DO NOT work / behave in the same way. They are not the same.

There is now scientific agreement that the controversy around isoflavones’ potential to have bad side effects in humans is fuelled only by findings from lab or animal studies using pure isoflavones (supplemented) in high doses. It is well established that animals metabolise isoflavones in a different way to humans and results from such studies cannot be compared to any human outcomes.

Additionally, using high doses of pure isoflavones cannot be compared to consuming isoflavones from whole soya foods which provide lower quantities and are a combination of many biologically active molecules.

Comprehensive reviews by the European Food Safety Authority, World Cancer Research Fund and the World Health Organisation all conclude that soya foods as part of a healthy balanced diet are safe.

Typical daily intakes of soy isoflavones in China and Japan are around 25-50mg. We in the UK are way below this at around 2mg but a 250ml glass of soya milk provides ~25mg. Not all soya foods are the same however, with some processing methods removing 80-90% of the isoflavones. This is certainly the case for isolated soya protein, used in soy protein powder. 

Reduce menopause symptoms

Many women undergoing the menopause experience ‘hot flushes’. Consuming 40mg of isoflavones daily, equivalent to ~2 glasses of soya milk or 100g soya mince, may help to reduce hot flush frequency by ~20% and severity by ~25%. 

Incidentally, reasonable intakes of soy foods and soy isoflavones do not affect men’s testosterone levels, oestrogen levels, or fertility.

Men  won’t start growing 36 DD’s unless, as case reports have documented, they are having incredibly high daily intakes of soy for 6–12 months.

Men who are at risk of developing prostate cancer might reduce their risk by eating soy foods, but soy foods do not appear to benefit men who already have prostate cancer.

Breast cancer

Despite high levels of estrogen being linked to an increased risk of breast cancer, eating moderate amounts of soy foods does NOT increase risk of breast cancer — or other types of cancer.

It is SAFE for pre and post menopausal women with breast cancer to have up to 3 servings a day, 1 serving being the same as one glass of soya milk.

For women with a history of breast cancer, soy foods may even play a role in reducing the risk of the cancer coming back.

I emphasise soy from foods rather than supplements here. We need more research looking into the effects of higher isoflavone doses included in supplements before I would recommend them. 

Gut health

It's very early days examining the impact of soy on gut health but there seems to be a link between isoflavones and the gut microbiome (your gut bacteria).

Soy is rich in soluble fibre which is well known to feed and support our gut bacteria without the downside of making you fart. When bacteria feed off soluble fibre, the by-products help blood sugar regulation, lower cholesterol and generally improve well-being. 

We also know that our gut bacteria convert two soy isoflavones - daidzein and genistein to a metabolite called equol. Research is suggesting equol could offer significant protection against chronic conditions, in people who have a good microbiome that is.

It appears only 20-30% of people in the UK have the right bacteria to make equol and would therefore benefit from consuming soya foods. This is compared to 50-60% of adults living in Asia who can create it very effectively.

Equol has also received attention for its ability to alleviate hot flushes, heart disease, osteoporosis and other menopausal symptoms. Diet as well as genes may play a role here too and probably other factors we don't even know about yet, so watch this space.  Studies are now looking at whether taking a probiotic with an isoflavone supplement can increase the production of equol from both genistein and daidzein. 

Helps lower cholesterol

Soya foods are naturally low in saturated fats and it's believed the soya protein itself helps to lower the body’s own and natural production of 'bad LDL cholesterol' by the liver.

There are no long-term studies that have assessed the effects of soy consumption or isoflavone supplementation on heart-disease outcomes but a large review of observational studies suggests soy consumption is associated with a reduced risk of heart disease. This is particularly important for menopausal women who develop an increased risk of developing heart disease due to the associated loss of oestrogen.

Concerns about GMO

The soyabean plant, is the number one genetically modified crop in the world. Non-GMO soyabeans have traditionally been used to make soya food products such as tofu, miso, and soya milk, while GM soybeans have been used for animal feed but there are concerns about GM soybeans moving into the human food industry. To be honest, this is a personal choice and if this worries you, go for organic soy products, of which there are many.

Thyroid function

Some animal studies have shown soy can have a hypothroidic effect. This may be because soy contains goitrogens; substances that interfere with iodine uptake in the thyroid gland and also the isoflavones that inhibit enzymes essential to thyroid-hormone synthesis. HOWEVER, these effects have NOT been seen in humans. Studies that have examined the effect of phytoestrogen and goitrogen supplements showed there was no effect on thyroid function.


These are components of plants like  tannins, phytates, oxalates that  interfere with the digestion and absorption minerals, particularly iron, zinc and calcium. Anti-nutrients hold onto these minerals, preventing us from absorbing them easily.

In the UK however, many soya food are fortified with extra calcium (vitamin D and sometimes other nutrients) meaning the mineral content and absorption compares favourably with dairy foods.

Studies also show these minerals are actually absorbed well from soya foods when eaten as part of a mixed diet. The human body also adapts to absorb more of these minerals when reserves are low.

To be honest, the soybeans we buy and consume are processed (either soaked, boiled fermented, roasted or tinned) to make milk, tofu, flours and powders which significantly reduces the activity of these anti-nutrients too. So they really aren't much to bother about, particularly as I doubt you will be living purely on soya products alone.

So I hope this clears some of the muddy waters that surround soy. The bottom line being they can be a fantastic addition to a healthy diet and you may receive multiple benefits from doing so.


1 comment

  • Gurdeep Singh

    I have been drinking and eating Soya products for 10 years and they have helped me with my Chrons as being lactose intolerant. Being a vegetarian I found getting protein from Soya based products has helped me just as much if not more than when I used to consume meats. This article confirms my own beliefs of why I chose to consume Soya, and can continue to enjoy without the fear of health effects that Soya could cause as claimed by some.

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