Will Soy or Soy products cause breast cancer?

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Soy and soy products are very popular in eastern cultures. It is widely consumed in Asia, especially in China and Japan. The per capita intake in Japan is more than 10 times that of the USA and Europe. They are consumed in various forms, the most popular being soy milk, soy drinks, soybean curds, and various fermented soy foods, unique to the different cultures.

Many health benefits have been linked to consuming soy and its products. These benefits can be attributed to soy being a source of proteins, antioxidants, and phytoestrogens. The benefits include protection against age-related degenerative diseases such as cardiovascular disease, osteoporosis, and dementia; reduction of symptoms related to female hormonal imbalance and menopause; and estrogen-dependent cancers. The influence of soy on breast cancer has received much attention lately, not only because breast cancer continues to be the top killer cancer for women in many countries, but also because there have been conflicting and confusing results of studies done on soy and its influence on breast cancer.

It has been observed that women in the countries where soy and soy products) are regularly consumed get breast cancer less often than those in Western countries. For example, the prevalence of breast cancer in China is much less than in the USA. Among the reasons could be that the Chinese women consume much more soy milk, while the US women consume more cow’s milk (cow’s milk protein is a known cancer promoter).

This observation led to studies to establish more clearly the relationship between soy and breast cancer. Many studies have now established that the earlier (eg. before adolescence) the women start high consumption of soy-based foods, the higher is the protection. And this protection is enhanced if the women continue the consumption into later life. However, if the high consumption of soy starts only in later life, then the protection is less.

The active ingredients of soy that affect breast cancer development, gress, recurrence, and prognosis arits isoflavones, which are a class of phytoestrogens — which means ey are phytochemicals that have a weak effect on the estrogen receptors of cells (particularly of the female organs such as breasts, uterus, and vagina, and also other organs like the brain, heart, skin, and bones.

Some studies showed that soy isoflavones protect against breast cancer, while others showed that they promote cancer growth. It is therefore important that we understand the science behind all this, so that we have the right picture, and know exactly when it is beneficial for women to consume soy products, and when it is not.

The latest research, which has led us to a better understanding of the conflicting study results, showed that soy isoflavones can have both estrogenic (mimics estrogen) or
anti-estrogenic (opposes estrogen) effects on those cells and organs. So the net result is the balance between these opposing effects.

Many laboratory studies show that soy isoflavones stop breast cancer cell growth or induce their death (apoptosis), and studies on humans consistently show that soy isoflavones reduce the risk of breast cancer, and women who continued to consume soy after being diagnosed with breast cancer had significantly lower rates of recurrence compared with women who consumed less or no soy.

The different and confusing results obtained in the lab may also be because of the different test lab environments; different types of soy food or soy products used, and many other factors that operate in the living person compared to the lab animals) that may account for the opposite responses.

In other words, soy isoflavones metabolism differs between humans and animals and therefore the outcomes of animal studies may not be applicable to humans.

Apart from the phytoestrogens, is voneshaeother (non-hormonal) and-cancer actions. Isoflavones can prevent cancer development or progress by inhibiting the enzymes required for DNA replication and metastasis; disabling growth factors that promote angiogenesis (growth of new blood vessels to feed cancer), and activating the immune system.

So on one hand there is the worry that soy isoflavones may worsen breast cancer. On the other hand, soy isoflavones are also being studied as possible treatments for breast cancer! Obviously, more research is needed to settle this confusion.

1. Soy isoflavones can help prevent the development of breast cancer, especially if regular consumption starts from young. The earlier, the better! Regular consumption means consuming soy or soy products almost every day.
2. Soy isoflavones give stronger protection from breast cancer if women continue consuming soy isoflavones from young to later life.
3. Soy isoflavones can protect (although less effectively) from breast cancer. Women only start consuming soy isoflavones later in life.

4. Although lab results Post-menopausal have been conflicting, the current evidence in human studies is that it is beneficial even for women with breast cancer (who have been consuming soy isoflavones) to continue consuming isoflavones.

5. Women with breast cancer who are not regular consumers of soy since young may have to be cautious about taking soy isoflavones (until more research settles the controversy). Some experts extend the caution to include women without breast cancer but who are at high risk.

6. Post-menopausal women who do not have breast cancer may benefit from the reduction of menopausal symptoms, reduction of breast cancer risk, plus other benefits (for the heart, brain, bones, etc.)

7. Soy isoflavones are known to affect thyroid hormone metabolism, but this does not affect those with healthy thyroid function. However, those with hypothyroidism (low thyroid function) are not encouraged to consume soy or soy products.

In conclusion, ALL women from adolescents to post-menopausal (except for those with breast cancer who are not already regular consumers of soy foods or products, and those with hypothyroidism) can benefit from soy isoflavones.