Most of the advice about reducing breast cancer risk focuses on things to avoid, like obesity, alcohol, or hormone therapy in post-menopausal women. But like miners endlessly panning a muddy streambed searching for gold, researchers have continued to look for positive dietary factors that might lessen a woman's chances of eventually developing this potentially fatal disease. So far, this hunt for nutritional barriers to breast cancer development has not met with great success. Nevertheless the search continues, as many medical experts are convinced that healthy foods do have some kind of protective effect against disease in general, even if precise links to specific diseases like breast cancer have so far remained elusive.
Despite the lack of conclusive proof, however, advocates for certain foods and nutritional supplements occasionally make claims about the ability of those substances to prevent or lessen the severity of breast cancer, usually based on some pieces of evidence that while not conclusive do suggest a possible effect. One of the most frequently mentioned food items in this category is soy.
We have probably all heard soy touted as a food source because of its many alleged health benefits, including its capacity to protect women from breast cancer. Anecdotally, it has been noted that Japanese women, who generally consume soy-based food products on a daily basis, have much lower breast cancer rates than American women for example, and it has been speculated that a diet heavy in soy may be one important reason.
One problem in assessing the true health promoting properties of soy is that it has so many enthusiastic boosters that it can be difficult to trust everything you hear or read. Fortunately, controlled studies on the question have been performed, so it is not necessary to take anyone's word for it about the breast cancer protecting qualities of soy, for example - you can investigate and discover the truth for yourself.
Eastern Asian Diets and Breast Cancer
There have not been a plethora of controlled studies performed to explore a possible connection between soy consumption and reduced risk of breast cancer. While some studies have been undertaken, so far these attempts have not provided a satisfactory answer one way of the other. Nevertheless, many have openly expressed the opinion that soy products can help women avoid breast cancer, and even help them overcome it once it has been diagnosed. The reason why some have stated this with so much confidence is because of the relatively low levels of breast cancer found in women from Japan and other East Asian countries, where soy consumption is ten times higher than that of women in the United States.
Soy contains many health-promoting nutrients; but with respect to the possible prevention of breast cancer, speculation has centered on substances called isoflavones that are abundant in soy products. Isoflavones are a type of phytoestrogen, which are estrogens that come from plant sources. The hormone estrogen is produced in the human body for the purposes of reproduction, and its presence has been linked to the development of breast cancer. About 75% of all breast cancers fall into the category of estrogen-receptor positive, which means they have receptors on the surfaces of their cells that can bind with estrogen, absorb it into the body of the cancer cell, and use it as a fuel source to power faster growth and cell division. If relatively weak estrogens like isoflavones were to bind with estrogen-receptors instead of human estrogen, however, it is possible they would not be strong enough to be used effectively by cancer cells, which means that phytoestrogens like these might act to pre-emptively subvert the further development of estrogen-receptor cancer cells.
This concept is largely theoretical at the moment; but given what is known about how estrogen-receptor positive cancers function, it does make a certain amount of sense, and it could explain why soy appears to have a protective effect against breast cancer in those women who eat a lot of it.
Despite the logic behind the isoflavone/estrogen-receptor binding theory, there is reason to be somewhat skeptical of the idea that the breast cancer rates of East Asian women can be entirely explained by their consumption of soy. These women use soy as their primary protein source, which means it is largely replacing beef, pork, and chicken in their diets. Because they do not consume these foods, East Asian women do not take in as many saturated animal fats as women who eat the typical western diet, and they are also not indirectly consuming the growth hormones and antibiotics that are given in prodigious amounts to farm animals by modern factory farmers. East Asian women also eat more fresh vegetables than American women, are more physically active, drink less alcohol, and have lower rates of obesity - all of which could help to lower the risk of breast cancer. So while the soy that East Asian women eat could be playing a role in reducing their chances of getting breast cancer, there is really no way to totally isolate that potential effect from other possible dietary factors.
The Protective Abilities of Soy: What the Research Reveals
Researchers at the Aichi Cancer Center Research Institute in Japan performed the most comprehensive research study on the anti-breast cancer properties of soy that has been carried out to date, the results of which were published in 2008. Using complicated protocols involving women afflicted with breast cancer and a large control group, they discovered that soy consumption had a clear and demonstrable effect on breast cancer rates for certain types of the disease. Specifically, they found that soy could be linked to breast cancer risk reduction for two major varieties of the disease - estrogen-receptor positive and HER2 negative. The cancerous cells of the former are able to bind with the body's estrogen molecules and absorb them as a food source, while the latter is a fast-acting, aggressive cancer that produces an abundance of the HER2/neu protein.
Given that these two types of breast cancer comprise 80 to 90% of all breast cancers diagnosed, the protection offered by soy is actually quite comprehensive. What this Japanese study found is that women with the highest levels of soy consumption had a 26% reduced risk for estrogen-receptor positive cancers, and a 22% reduced risk for HER2 negative cancers in comparison with the women in the study who consumed the least amount of soy.
An even more recently published report in the Canadian Medical Association Journal looked specifically at the effects of soy consumption on postmenopausal breast cancer victims. In this case, researchers were studying breast cancer recurrence rates, and these data revealed that women with the highest levels of soy consumption had a 33% lower rate of recurrence than women who ate little soy. This study also found a connection to hormone receptor status, as cancers positive for both estrogen and another female hormone, progesterone, showed the greatest recurrence risk decrease in coordination with significant soy consumption.
According to a paper just recently introduced at the American Association for Cancer Research's 102nd Annual Meeting, multiple studies in the US and China have found an overall reduction of about 9% in mortality rates, and 15% in breast cancer recurrence rates for women who consumed more than 23 mg. of soy per day, in comparison to those who consumed very little. This report went on to suggest that higher levels of soy consumption could produce even more significant reductions in breast cancer mortality and recurrence.
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