Vegan for Life - Jack Norris [82]
An alternative explanation is that some soy products may be more effective at minimizing the effects of hot flashes than others. In one comprehensive analysis of seventeen studies, the supplements that were most effective were those that had an isoflavone pattern similar to soybeans. For example, soyfoods are typically rich in an isoflavone called genistein; supplements in which at least half of their total isoflavone content was in the form of genistein were very effective in studies. Consuming an amount of isoflavones that is equivalent to approximately two servings of soyfoods consistently reduced the frequency and severity of hot flashes by about 50 percent. For women who have as many as seven to ten hot flashes per day, a 50 percent reduction can provide significant relief.
Breast Cancer
In 1990, the National Cancer Institute began looking at soyfoods and isoflavones as a possible way to reduce the risk of cancer.35 While their interest was in all cancers, they placed a particular focus on breast cancer. Most breast tumors are stimulated by estrogen, and there was evidence early on that isoflavones could have anti-estrogenic effects on breast tissue.36,37 In addition, the historically low rates of breast cancer in Asia suggested that there was something about an Asian lifestyle that was protective.38
Twenty years later, the effect of soy consumption on cancer risk remains a question mark. Soy detractors have suggested that soy is not protective and may, in fact, be harmful for women at risk for breast cancer. However, the most recent evidence, as we’ll see below, suggests that soyfoods may actually be beneficial for breast cancer patients.
Certain types of studies in mice have raised questions about soy consumption for women who have estrogen-positive breast tumors (the kind that are stimulated by estrogen).39 But humans and mice have very different physiologic responses to isoflavones, which means the relevance of these findings to humans is uncertain. Furthermore, even in the animal studies, whole soyfoods didn’t have adverse effects.40 More importantly, studies of women show that neither whole soyfoods nor isoflavone supplements have harmful effects on indicators of breast cancer risk, such as breast cell proliferation and breast tissue density.41 The position of the American Cancer Society is that breast cancer patients can safely consume up to three servings of traditional soyfoods daily.42
In fact, new epidemiologic studies show that women who consume soyfoods after a diagnosis of breast cancer have an improved prognosis. A Chinese study involving more than 5,000 women with breast cancer found that those who consumed the most soy after their diagnosis—about two servings per day—were about one-third less likely to have a cancer recurrence or to die from their disease compared with women who consumed little soy.43 Eating soy was found to be as protective as taking the breast cancer drug tamoxifen.
A much smaller study, also from China, showed similar findings in postmenopausal breast cancer patients.44 This study also found that soyfood consumption enhanced the efficacy of one of the most commonly used types of breast cancer drugs. Because these were epidemiologic studies, and because they involved Chinese women who almost certainly had consumed soy throughout their lives, we have to use care in interpreting the results for western women. But the evidence increasingly suggests that soy is safe and even potentially beneficial for women with breast cancer.
This, of course, raises