Soy products constitute a huge part of our diet and daily intake, since it can be found easily and is a highly versatile ingredient used to make everyday food products. However, for breast cancer patients and those at risk, is consuming soy a boon or bane? We explore both sides of the theory that soy increases risk of recurrence and appearance of breast cancer.
by Lim Wan Er
What are they?
In this age with substantial technology advancements, screening and treatment has improved for breast cancer patients. Being one of the most common types of cancer found in women, breast cancer is also the second primary cause of death after lung cancer.1
As its name suggests, breast cancer originates from a malignant tumour in the breast. When breast cells deviate from the normal division and production process, the cells grow and divide out of control. Atypical extra tissue is formed, resulting in a mass or lump also known as a tumour. The breast is made up of fat and gland cells, where the glands that produce milk are known as the milk ducts. Most breast cancers originate from the milk ducts, and a minority from the milk sacs or lobules. These milk ducts consist of standalone cells that reproduce with the help of hormones produced in the human body. Cancer starts when the cell reproduction process malfunctions and develops a tumour over time.2
Superfood or poison?
You may have heard that you should avoid soy food to reduce your risk of breast cancer. Somehow, there is also another saying that soy could protect you against the cancer. Is there really a link between soy intake and an increased risk of breast cancer? Wendy Chen, a breast oncologist with the Susan F. Smith Center for Women’s Cancers at Dana-Farber, Massachusetts, U.S., mentioned that the above question is asked frequently.5
A substantial amount of soy is being consumed around the world, due to it being an inexpensive and widely accessible source of protein. It is also an exceptional alternative to meat-based protein, especially in vegan meals in the form of mock meat. A traditional Asian meal, most often than not, would contain tofu or edamame as a side, with a soy sauce stir-fried main, coupled with fragrant rice. Children and adults who are lactose intolerant will make soy milk a huge part of their diet as well. Therefore, there is a biological foundation for this question and it is indeed what many people are concerned about.
There are two camps on whether soy-based foods should be consumed by women with a history of breast cancer or are currently diagnosed with breast cancer. These soy-based foods include mainly soy milk, edamame, tofu, and beans – generally foods that are produced using soy beans.
Past studies have suggested that isoflavones (a group of phytoestrogens and an estrogen-like compound) found in soy foods may curb the recurrence and appearance of breast cancer.3 On the other hand, there are also studies which advise that isoflavones increases cancer risk as breast cancer is strongly associated with estrogens. There has been controversy over whether the isoflavones could increase the risk of breast cancer since estrogen interferes with hormone blockade agents used in breast cancer aftercare4 and reduces the effectiveness of cancer drugs.3 This has resulted in confusing messages about the relation between soy consumption and breast cancer, and more research regarding this aspect has been explored over the years.
Nonetheless, the current consensus among health researchers is that soy food consumption is not dangerous for breast cancer patients and does not have a detrimental consequence. Some suggest that the confusion arises from phytoestrogen in soy, mainly isoflavones, which have “chemical structures that look like the estrogen found in women”.7 Phytoestrogens are “naturally occurring plant compounds” that look structurally like estrogens and may have weak estrogenic actions, 8but they are not the same as estrogens found in a human body.
Several large-scale human studies show that women who regularly eat soy have a lower breast cancer risk as compared to those who do not. Some studies also reflect that soy food consumption lowers the risk of breast cancer recurrence.7 In fact, for some people, soy seems beneficial for a longer lifespan after breast cancer.3 Fang Fang Zhang, a cancer epidemiologist at Tufts University, Massachusetts, U.S., based her findings on a study of approximately six thousand American and Canadian women. She found that there is a “21 percent reduction in all-cause mortality” among the women who had the highest soy intake, as compared to those with the lowest intake. Another 2009 study consisting of five thousand Chinese breast cancer survivors showed that those who consumed the most amounts of soy products healed better in the following four years after diagnosis and treatment.3 Nonetheless, these are observational studies which are not able to pin-point if soy consumption really has an evident relation to breast cancer.
Keep up the exercise
For instance, the research participants could have been health conscious people who exercised regularly and maintained a less oil, high fiber diet.7 In a recent breast cancer study conducted on 7,663 women in Malaysia (3,683 breast cancer cases, 3,980 healthy women), Associate Professor Ho Weang Kee from the University of Nottingham, lead statistician in the study said, “physically active women have a 30 to 60 per cent reduced risk of developing breast cancer."9
Know the difference
One point to keep in mind is that there is an apparent difference between whole soy foods and other processed soy products such as soy protein isolates and dietary supplements. One relatable representation is that the former includes foods such as edamame, miso, soymilk, soy nuts, tofu, tempeh and whole soybeans, among a list of other products. Whole soy foods have numerous health benefits such as lowering cholesterol levels and even offering protection against some cancers. These whole foods are minimally or non-processed options and should not be confused with meat substitutes made from soy.
Processed soy products include soy protein isolates, which is a supplement or additive. It is found in nutrition bars that we sometimes consume as meal replacements or vegetarian mock meat products.5 Meat substitutes are often high in sodium content and loaded with added fat – a not so healthy option.6 Dietary supplements like soy pills and isoflavone-enriched powders should also be avoided,7 if they are not prescribed by an authorised health professional. If you are itching for something sweet to curb your cravings, the occasional soy protein bar is fine. Keep in mind that the less processed food you consume, the better it is overall for your body and health.
Moderation is key
All in all, there is no concrete evidence that proves that taking soy in large amounts is beneficial in preventing breast cancer. Likewise, there is also no proof that the isoflavones in soy is the main cause of breast cancer and/or the recurrence of it. As advised by health practitioners, all foods should be taken in moderation. Remember, too much of anything is not necessarily a good thing.