Soy & Health - Update

Bread containing soy grits may reduce risk of prostate cancer development and progression

A study published in the journal Urology by Dr Fabien Dalais and HEC's Professor Mark Wahlqvist in September 2004 showed that a daily diet containing four slices of a bread rich in soy grits favorably influences the PSA level and the free/total PSA ratio in patients with prostate cancer. This work provides some evidence to support epidemiologic studies claiming that male populations who consume high phytoestrogen diets have a reduced risk of prostate cancer development and progression.

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The scientific literature currently supports the following roles for soy (taken from The Nutrition Society of Australia Seminar Series in July 2002 & scientific papers in 2002):

about 2-3 serves of whole soy foods per day (soy protein in combination with phytoestrogens) can lower total and LDL cholesterol levels; the higher your initial blood cholesterol level the greater the effect. It is not yet certain if it is the soy protein or the phytoestrogens (or the two working together) which are having the effect.

soy protein in combination with phytoestrogens can reduce blood pressure in healthy people as well as treated and untreated people with high blood pressure. (Rivas et al., J Nutr 2002; 132: 1900-2)

soy phytoestrogens may improve blood vessel function (improved arterial elasticity and compliance, smooth muscle cell function and improved function of cells lining the vessels or endothelium) - more research needed

soy phytoestrogens may reduce oxidative stress - more research needed

whole soy foods have cardiovascular benefits; the benefits in taking phytoestrogen supplements alone are unproven.

2-3 serves of whole soy foods per day is associated with 50-60% improvement in menopausal symptoms over 12 weeks; wholegrain cereals can also reduce hot flushes; there is not enough evidence that phytoestrogens alone (in supplements or added to food) are effective. (Newton et al., Obstet Gynecol 2002; 100: 18-25)

There is emerging evidence that soy foods may play a role in protecting bone and building bone mineral density and thus may help reduce the impact of osteoporosis. (Albertazzi, Climacteric 2002; 5 (2): 190-6). The World Health Organisation in 2002 rated the level of evidence for soy products decreasing the risk of osteoporosis as "possible".

There is emerging evidence that soy foods may protect against breast cancer (Jakes et al., Cancer Epidemiol Biomarkers Prev 2002; 11(7): 608-13.

It is well known that high levels of oestrogen increases the risk of cancer of the uterus.
This is why obese women (fat tissue produces oestrogen) have increased uterine cancer. Phytoestrogens have the potential to lower the levels of oestrogen produced by the body and theoretically reduce the risk of this cancer. A case control study of 500 women in the US diagnosed with endometrial cancer and a similar number of controls found that women who consumed the most phytoestrogens had half the risk of this cancer compared to women who ate the least. This study was published in 2003 August 6 Journal of the National Cancer Institute.

When purchasing soy containg foods check the ingredient list to ensure they are made from whole soy beans and ensure that products such as cereals contain soy protein and not just added isoflavones (wholegrain cereals, nuts, tahini, linseed, extra virgin olive oil and other legumes like chickpeas also naturally contain phytoestrogens).

Further Reading: Wahlqvist ML, Dalais FS. Phytoestrogens: emerging multifaceted plant compounds. MJA Vol 167; 4 August 1997: pp119.

Click here to read a newspaper article publsihed in the Herald last year on SOY

Last Updated: September 2004