Poliquin Live

Tip 222: Avoid Soy and Dairy and Decrease Prostate and Breast Cancer Risk

Thursday, November 24, 2011 8:11 AM
Eliminate soy and dairy from your diet and decrease prostate and breast cancer risk. Soy and cows’ milk have been shown to increase the growth rate of breast and prostate cancer cells indicating it’s prudent to avoid both in your diet. 

Soy contains phyto-estrogens called isoflavones, which are plant-based chemicals that mimic estrogen in the body.  They work in a similar way to manmade chemicals such as BPA that have an estrogenic effect. Most soy produced today is made from genetically modified organisms (GMOs), which is another reason why it should not be part of your diet. Men should avoid soy because it has been shown to lower testosterone, while women of reproductive age should also steer clear because soy will increase breast cancer risk and can lead to an androgen imbalance and poor body composition.

A new study in the journal Nutrition and Cancer tested the in vitro effect of milk from cows, almonds, and soy on breast and prostate cancer cells. Cows’ milk stimulated the growth of prostate cancer cells, producing an average increase in cancer cell growth rate of over 30 percent. Almond milk suppressed the growth of prostate cancer by over 30 percent, indicating that almonds should be part your diet and that  almond milk is a perfect alternative to cow or soy milk. Researchers caution that elevated levels of estrogens in cows’ milk may be the source of the increased cancer cell growth.

A second study in the Asia Pacific Journal of Clinical Nutrition supports the link between prostate cancer rates and dairy consumption and suggests that along with the estrogenic hormones in dairy, high calcium levels may also contribute to prostate cancer rates. 
In the first study in Nutrition and Cancer, soy milk increased the growth rate of breast cancer cells significantly and it should be avoided in men and women. Even though this was an in vitro study of cancer cells in a test tube, there is evidence that soy and dairy can alter endocrine levels in humans.

A new study in the American Journal of Epidemiology looked at the relationship between soy intake in the diets of Japanese children and their androgen hormone levels. In young girls, greater soy intake was linked to a significant increase in testosterone, but there was no statistical link between estrogen levels and soy intake. For young boys, greater soy intake didn’t affect testosterone but it did lead to lower estrogen levels.  Researchers suggest that soy inhibits the conversion of androgens to estrogens in boys, leading to lower estrogen. For girls, the same process leads to higher testosterone in girls who normally have minimal levels of this hormone. 

Although this evidence might lead you to think eating a lot of soy is good for lowering estrogen, I suggest you look closer. Similar hormonal responses in males and females have been seen following exposure to BPA, which mimics estrogen and raises testosterone in females. But BPA exposure has been shown to significantly lower testosterone in males and result in poor reproductive health and fertility. Equally, the concern with soy for men is that although it lowers estrogen, excess intake will result in lower testosterone as well.
Some scientists suggest that soy can have protective effects on health because of how it alter human hormone metabolism. Healthy endocrine balance is more complicated and more essential for health than these scientists would suggest. BPA and other chemical xenoestrogens indicate the larger-dose effect of estrogen mimicking substances in the body, and despite an overabundance of data that such chemicals are a serious health risk, they are still in our food and environment in large quantities.

The best strategy is for men and women to eliminate soy and dairy from the diet. For women, small quantities of organic dairy are likely not problematic. The concern with even minimal amounts of soy for men is that almost all soy is genetically modified. To read more about the negatives of soy, read the Risks and Benefits of Soy.

Tate, P., Bibb, R., et al. Milk Stimulates Growth of Prostate Cancer Cells in Culture. Nutrition and Cancer. November 2011. Published Ahead of Print.

Wada, K., Nakamura, K., et al. Soy Intake and Urinary Sex Hormone Levels in Preschool Japanese Children. American Journal of Epidemiology. May 2011. 173(9), 998-1003.

 Qin, L., Wang, P., et al. Estrogen: One of the Risk Factors in Milk for Prostate Cancer. Medical Hypotheses. 2004. 62(1), 133-142.

Qin, L., Xu, J., et al. Milk Consumption is a Risk Factor for Prostate Cancer in Western Countries: Evidence from Cohort Studies. Asia Pacific Journal of Clinical Nutrition. 2007. 16(3), 467-476.

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