Anybody who has had breast cancer should avoid traditional soyfoods such as tofu and soymilk.
|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 equal, 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 studies, soyflour, which is a minimally processed soyfood, doesn’t stimulate tumor growth .
Furthermore, and most importantly, the human evidence is very supportive of safety. Neither isoflavone supplements nor soyfoods adversely affect markers or indicators of breast cancer risk [7, 8]. 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 suggesting soyfoods are likely to be harmful to breast cancer patients. Accordingly, in 2006, the American Cancer Society stated that breast cancer patients can safely consume up to three servings of traditional soyfoods daily .
In fact, there is evidence suggesting that breast cancer patients may benefit by consuming soyfoods. A recently published study in the Journal of the American Medical Association (JAMA) found that among Chinese breast cancer patients, those who consumed the most soyfoods were about 30% less likely to die from breast cancer or to experience breast cancer recurrence over a four year period compared to patients with the lowest intake of soy . One other study also reported that patients with estrogen-sensitive breast cancer would benefit by consuming soy . In an editorial accompanying the article in the JAMA, researchers from the National Cancer Institute and the Fred Hutchinson Cancer Research Center in Seattle stated that “… clinicians can advise their patients with breast cancer that soyfoods are safe to eat and that these foods may offer some protective benefit for long-term health .”
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