Although elevated cholesterol levels are most closely associated with heart disease, there is also evidence that they could raise risk for breast cancer. According to researchers from Duke University Medical School and several other institutions, a metabolite of cholesterol called 27HC turns into a potent estrogen-like molecule that could affect risk of breast cancer. Therefore, it is possible that approaches to lowering blood cholesterol may help to prevent and treat breast cancer. Consuming more soyfoods may be one of those effective approaches.…
Recent research has brought reassurance to women who enjoy soyfoods, especially those who have had breast cancer. Last year, both the American Cancer Society and the American Institute for Cancer Research concluded that women with breast cancer can safely consume soyfoods. And now, another study adds even more support to that stance….
Traditional soyfoods such as tofu and soymilk increase risk of tumor recurrence in breast cancer patients.
|There is essentially no human evidence indicating that traditional soyfoods increase tumor recurrence in breast cancer patients. In fact, there is evidence suggesting consuming soyfoods may actually be of benefit to such women.|
Breast cancer incidence and mortality rates in soyfood-consuming countries such as Japan are much lower than they are in Western countries . Several factors likely contribute to the differing breast cancer rates of these two regions. One may be the high soy consumption in Asia. There is in fact an impressive body of evidence suggesting soyfoods reduce risk of breast cancer. However, studies in support of this hypothesis indicate that to derive the proposed benefit soyfoods must be consumed during childhood and/or adolescence. Consuming as little as one serving per day may be enough to reduce risk later in life by as much as 25 to 50 percent [2, 3].
Despite the proposed benefits there is also concern that soyfoods might be harmful to some types of breast cancer patients. More specifically, there is concern that the isoflavones in soyfoods could stimulate the growth of estrogen-sensitive tumors – these are tumors whose growth is stimulated by the hormone estrogen .
Isoflavones are naturally-occurring constituents of soybeans that are commonly referred to as plant estrogens or phytoestrogens. There are many different types of phytoestrogens in foods (such as lignans in flaxseed) but soy is definitely one of the richest sources. However, isoflavones and estrogen are not equivalent, they have different chemical structures and although they share some properties in common they are also very different. That these two molecules are different is not at all surprising. Small differences in chemical structure can result in very different physiological effects. Consider the example of cholesterol, which is found in animal foods, and phytosterols, which are found in plants; these two molecules have almost identical chemical structures but the former raises blood cholesterol levels and the latter decreases them .
The primary basis for concern about isoflavones is the finding that when isolated isoflavones and certain types of isoflavone-rich products are added to the diets of mice with existing estrogen-sensitive tumors, tumor growth is stimulated  However, not only are the results from animal studies often not predictive of events in humans, but even in the animal model in which isoflavones stimulate tumor growth, soyflour, which is a minimally processed soyfood, doesn’t stimulate tumor growth . Furthermore, not even all animal studies show isoflavones are tumor-stimulatory  .
In addition, and more importantly, the human evidence is very supportive of safety. In human intervention studies, neither isoflavone supplements nor soyfoods adversely affect markers or indicators of breast cancer risk [8-10]. Markers of breast cancer risk include breast tissue density, which is measured via mammography, breast cell proliferation, which requires that breast biopsies be taken, and blood estrogen levels. Thus, there is essentially no clinical evidence indicating soyfoods are likely to be harmful to breast cancer patients.
In fact, there is epidemiologic (population) evidence suggesting that breast cancer patients may benefit by consuming soyfoods. In 2012, a pooled analysis of three studies was published involving 9,514 breast cancer survivors, two of the studies were from the United States and one was from China . Approximately half of the study participants were Caucasian and half Chinese and approximately half were premenopausal and half postmenopausal. Over the 7.4 year period the breast cancer survivors were followed, those women in the group who ate the most soy, were 13% less likely to die from any cause, 17% less likely to die from breast cancer and 25% less likely to report having a recurrence of their disease . The last finding was statistically significant, which in scientific parlance indicates the finding was unlikely to have occurred by chance.
Not surprisingly, based on the clinical and epidemiologic evidence, in 2012, both the American Institute for Cancer Research and the American Cancer Society concluded that soyfoods can be safely consumed by breast cancer patients . Interestingly, on the basis of their analysis of the scientific literature, Chinese researchers recently recommended that breast cancer patients incorporate soy into their diet specifically for the purpose of improving their prognosis .
Finally, it is important to remember that many breast cancer patients will live for many years without succumbing, and many others, will never succumb, to their disease . Therefore, all cancer survivors need to consume a diet that is not only protective against cancer recurrence but that is protective against a range of chronic disease such as coronary heart disease. Soyfoods are certainly well-positioned to be part of that diet .
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2. Messina M, Hilakivi-Clarke L: Early intake appears to be the key to the proposed protective effects of soy intake against breast cancer. Nutr Cancer 2009, 61(6):792-798.
3. Messina M, Wu AH: Perspectives on the soy-breast cancer relation. Am J Clin Nutr 2009, 89(5):1673S-1679S.
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Research on soy along with the growing interest in potential health benefits of these foods focuses largely on their phytoestrogen estrogen content. These plant estrogens, called isoflavones, have been shown to reduce menopausal symptoms such as hot flashes, and may also reduce heart disease risk by improving health of the arteries….
Most epidemiologic research indicates that higher soyfood intake is associated with a decreased risk of breast cancer. However, most of this research consists of case-control studies, a type of study design that carries less scientific weight than prospective studies. In prospective studies, researchers enroll healthy participants into the study and follow them for a period of years in order to determine whether those with particular lifestyle habits are more or less like to develop a particular disease. A just-published Japanese prospective study confirms that high soy intake is associated with a lower risk of breast cancer….
It’s been nearly 20 years since the first research suggested a link between early soyfood consumption and a reduced risk for breast cancer. Researchers believe that consuming soy isoflavones during puberty can affect breast cell development in a way that provides protection against cancer. Since then, several studies have confirmed this relationship in Asian women but there have been fewer findings among non-Asians.
New research from Canada suggests that soy may be protective in Caucasian women as well. Women with and without breast cancer filled out a food frequency questionnaire designed to assess isoflavone intake within the past two years and also during puberty and early adolescence. In this study, adult intake of soyfoods wasn’t associated with risk for breast cancer. However, women who consumed the most soy isoflavones during their teenage years were about 20% less like to have cancer later on in life.
Isoflavones were protective primarily against estrogen-sensitive breast cancer, that is, breast cancer whose growth is stimulated by estrogen. More importantly, the women in this study consumed very little soy during adolescence since soyfoods were not commonly consumed at that time. This raises questions about whether such low intakes of soy isoflavones could possibly be protective. But while further research is needed to confirm the findings, they add to the growing body of data suggesting a protective role for soyfoods in the diets of young girls.
Anderson LN, Cotterchio M, Boucher BA, Kreiger N. Phytoestrogen intake from foods, during adolescence and adulthood, and risk of breast cancer by estrogen and progesterone receptor (ERPR) tumour subgroup among Ontario women. Int J Cancer 2012.
Researchers Dr. Pamela J. Magee from the University of Ulster and Dr. Ian Rowland from the University of Reading (United Kingdom) extensively reviewed the evidence related to soyfood consumption and breast cancer risk (2). They looked at studies focusing on prevention as well as prognosis in women who have had breast cancer….