Soya - Good or Bad for Us?

What is soya?

Soya-based products are made from the soya bean, originally found in parts of East Asia. This bean is high in protein and is the main source of protein for many communities. It can be a good alternative to meat products.

Soya products can now be found in many local supermarkets around the world, as the demand for dairy and meat replacements increases.

Types of Soya Products Available in the UK

These include:

  • Soya milk
  • Soya yogurts
  • Soya sauce
  • Tofu (silken and normal)
  • Fermented bean paste
  • Edamame beans (fresh, frozen, roasted, dried)

The soya bean contains a number of elements which may be beneficial for health including chemicals called isoflavones which may help menopasual and post-menopausal women. The picture is not totally clear, however, with some articles suggesting that soya products might not be as beneficial to our health as once was thought. We compare the evidence below.

Evidence to Suggest that Soya Might be Good for our Health

Soya contains a number of beneficial components such as:

  • Omega-3 fatty acids
  • Omega-6 fatty acids
  • Isoflavones
  • Vitamins and minerals such as vitamin K, Folate and Thiamin

It is also low in saturated fats.

Overall, studies have suggested that soya may have beneficial health effects, for post-menopausal women. For example:

  • High soy protein intake appears to increase HDL levels (‘good’ cholesterol) and reduce LDL cholesterol (‘bad’ cholesterol), triacylglycerol and total cholesterol levels – particularly for soy food compared with soy supplements.
  • It appears to decrease the risk of ischemic heart disease
  • It appears to decreases the risk of atherosclerosis and maintain blood vessel health, particularly if taken soon after the menopause (in line with the oestrogen timing hypothesis, which suggests soon after the menopause is the optimum time for health benefits from hormone therapy).  
  • It appears to reduce the risk of colorectal cancer risk in women (although not in men).

Breast cancer

While there is some evidence to the contrary, soya appears to reduces the risk of breast cancer reoccurrence. In particular an analysis of 9,514 breast cancer survivors who were followed for 7.4 years found that higher post-diagnosis soy intake was associated with a significant 25% reduction in tumour recurrence.  This is a significantly larger, longer term study than the ones which suggest increased risk. It focused on soya-based food consumption rather than soy supplements, and it focused on actual tumour growth rather than gene changes that might possibly lead to tumour growth. As such this evidence appears more robust and reliable than the more negative studies.

A Chinese analysis of existing research, published in 2015, also found people who ate soya-based foods appeared to have a reduced risk of breast cancer compared with people who ate high fat diets. The same was also true for people who ate more vegetables and more fruit.

A long term North American study with 6,235 ethnically diverse breast cancer survivors found those who consumed a high intake of soy products had a greater reduction in mortality risk than those who had a lower intake. However, lower mortality associated with higher intake was limited to women who had tumours that were negative for hormone receptors and those who did not receive hormone therapy for their breast cancer.

Bone Mass

There is also a reduction in spine bone loss in menopausal women consuming soya isoflavones compared to those who did not, with the greatest effect seen with those consuming more than 90mg a day. That’s according to an analysis of research, published in 2008. Soy isoflavones appear to reduce bone loss and promote the build up and maintenance of bone mass.

Prostate Cancer

In men with a greater risk of prostate cancer, high intake of soya-based product may reduce this risk. That’s the verdict of an analysis of mainly small, short term studies, which was published in 2014. A greater intake of non-fermented soya-based products has a greater beneficial effect over fermented soy-based products, according to a 2009 analysis of published research.

Non-fermented soy based products include:

  • Tofu
  • Soya flour
  • Soya milk
  • Raw soy beans

Fermented products include:

  • Miso
  • Natto
  • Tempeh
  • Natural brewed soy sauce

Evidence to Suggest that Soya Supplements might be Harmful for our Health

Whilst the evidence for soy based foods has tended to be positive, as indicated above, a number of studies have suggested possible health risks when it comes to the use of soy supplements, as opposed to soy based foods, although it should be noted these have tended to be short, small-scale studies. For example:

  • In 2007 the German Federal Institute for Risk Assessment advised against long-term consumption of isoflavone supplementation as it had been linked to alterations to the mammary gland structure and impairment to normal thyroid gland function.
  • A small study carried out over a short period of time (140 participants with early stage breast cancer over 7 – 30 days) found that women with early-stage breast cancer who were taking soy protein supplements might experience changes to gene expression that could potentially help cancer cells grow.
  • A review of published studies in 2010 suggested that consumption of isoflavone supplements may produce a modest increase in breast tissue density, a marker of increased breast cancer risk, in pre-menopausal (but not post-menopausal) women.
  • A 6 month trial with 126 women, published in 2012, suggested soya isoflavone supplementation probably wouldn’t prevent breast cancer and might possibly have an adverse effect in premenopausal women. However, the study did note that the trial was with a soya supplement rather than soya-based foods and that investigations of the potential of soy food intake, particularly early in life are reasonable.

As we have noted elsewhere, in our review of vitamins and minerals, taking supplements can sometimes increase health risks, whereas consuming food which contains the same vitamins and minerals is usually beneficial for health. A similar situation may apply to soy.


More research on soya is needed, for instance larger scale, longer term studies which focus on soya-based food (rather than soya-supplements) and the effects at different stages in life for Western women (to complement the larger number of studies among Asian women, who may have been consuming soya-based food from an early age). Also for men, including research into the possible initial prevention of prostate cancer (to complement existing research into the prevention of reoccurrence).

Overall though, the evidence to date suggests that:

  • Soya-based food (like soya milk and tofu) has greater health benefits and fewer risks than soy supplements.
  • Consumption from early in life appears to have a more protective effect (in particular for Asian women).
  • Soya-based food appears to have health benefits for post-menopausal women, if taken soon after the menopause, including better cholesterol levels, healthier blood vessels, reduced risk of heart disease, reduced bone loss, reduced hot flushes, reduced risk of colorectal cancer and reduced risk of breast cancer recurrence.
  • There is limited beneficial effect for men (other than possibly for prostate cancer), although more research is needed here.
  • There is a place for soy-based foods as part of a healthy balanced diet as it is a good source of protein and nutrients.

Isabel Morgan, February 2018. Next Review date February 2022.