Does Soy Worsen Breast Cancer?

The jury is still out on whether or not boosting the amount of soy in a woman's diet increases or decreases her chances of developing breast cancer. While some researchers believe increasing soy consumption is a prudent step towards preventing and treating estrogen-sensitive cancers like breast and uterine cancer, others say a soy-rich diet could make you more likely to develop such diseases and could even decrease your chances of recovery. Just to add more fuel to the fire, some medics even say that eating more soy is unlikely to have any effect on breast cancer risk or treatment whatsoever.

So what is a woman to do in this situation? First of all, if you are considering increasing the soy in your diet, you should read this page and then check out our article on the possible advantages of soy against breast cancer. Secondly you should always speak to your health care provider before starting a soy-rich diet; they will be able to help you weigh up the pros and cons. If you have already been diagnosed with breast cancer, or any other type or cancer, or if you have a history of breast cancer in your family, do not increase your soy consumption before speaking to your doctor. Lastly, read on to find out why some researchers think extra soy in your diet puts you in greater danger of developing, or dying from, this disease.

How Might Soy Worsen Breast Cancer?

Soy protein is a plant product found in foods such as soy sauce, tofu, roasted soy beans, etc. It contains isoflavones which may have the same effect as a weak estrogen on the female body. High estrogen levels are associated with the development and spread breast cancer, and therefore a key element of modern breast cancer treatment is to reduce or stop a woman's natural estrogen production. Proponents of increasing soy intake to fight breast cancer say that its weak-estrogen isoflavones encourage a woman's body to produce less estrogen, and therefore help the medical treatment on its way. However, other experts believe it makes no sense whatsoever to increase consumption of a product which adds estrogen to your system at a time when your medical treatment aims to cut down your estrogen levels. In this situation, eating more soy could make things worse, not better.  Another study has found that some isoflavones actually stimulate cancer growth when they occur in low levels in your body, but stop it at very high concentrations. You might think, ok, I just need to eat a lot of soy, but unfortunately it's not that simple. Experts say it's not possible to reach the high concentration of isoflavones required through diet alone. Therefore by eating more soy, you are likely to be achieving only the low levels of isoflavones which could encourage cancer growth.

Could Soy Cause Breast Cancer?

It is improbable that soy could be a lone factor in the development of breast cancer; but even so, it might be a good idea to limit your soy intake. In general, long-term exposure to high estrogen levels may make you more likely to develop the disease. Therefore supplementing your natural estrogen production with the plant estrogens in soy could increase your risk.

The Skeptics

It would be easy to walk away with the impression that soy is either good or bad for breast cancer, but this may not be case at all. Other studies have found little or no link between high-soy diets and breast cancer.


The answer to the question - "Does Soy Worsen Breast Cancer?" is quite simply - "We don't know (yet)." More research will have to be done and this may take many years. In the meantime, those who oppose the use of soy for breast cancer say it's better to play on the safe side and not increase the level of soy in your diet. The decision is yours at the end of the day, but it's not one that should be taken without the benefit of professional medical advice.

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