New research results show that women who’ve survived breast cancer should add legumes like soy and beans, nuts, and whole grains to their diet to prevent breast cancer recurrence.
Scientists looked at data from 22 studies that focused on soybeans, lignans (compounds found in seeds and nuts), cruciferous vegetables (crunchy veggies like cabbage, broccoli and cauliflower), and green tea. They also looked at the effect of phytonutrients found in these foods.
The study results were published in the medical journal ‘JNCI Cancer Spectrum’. The research was led by scientists at Johns Hopkins Kimmel Cancer Center at University in Baltimore, United States.
Beneficial isoflavones in soy
The study results show that intake of soy isoflavones from soy was linked to a 26% reduction in breast cancer recurrence.
The best results came from a daily intake of 60 milligrams -- that's equivalent to half-cup of cooked soybeans, 2-3 cups of soy milk, or three ounces of tofu.
The benefit of soy isoflavones in preventing breast cancer death was lower but reduced by only about 12%. That benefit was greatest when women ate about one or two servings of soy products per day.
According to the American Cancer Society: "Some studies have suggested that soy food intake might lower the risk of breast cancer coming back, although more research is needed to confirm this. While eating soy foods doesn’t seem to pose a risk, the evidence regarding the effects of taking soy or isoflavone supplements, which often contain much higher levels of these compounds, is not as clear."
It is not yet possible to determine “whether starting to consume these diets after diagnosis has the same effect as a lifelong dietary habit before diagnosis” said Dr Channing Paller, the study author and an associate professor of oncology at Johns Hopkins. That’s information that “patients are looking for,” he said.
Beneficial lignans in plant-based foods
Paller's team also looked at lignans, which are found in many plants such as seeds, nuts, legumes, whole grains, fruits, and vegetables. Flaxseeds, cashew nuts, broccoli and brussels sprouts contain exceptionally high concentrations of lignans.
High levels of enterolactone -- formed when lignans are broken down by the digestive system -- appeared to reduce the odds for death from breast cancer by 28%, the study found, and to cut the odds for an early death from any cause by 31%.
The lignan and soy findings were solid enough to recommend that breast cancer survivors use them in any dietary guidelines.
Other findings didn't have enough data behind them for that, but were "suggestive," the researchers said.
Beneficial phytonutrients in green tea
For example, they found that drinking lots of green tea was tied to a 44% reduction in breast cancer return for women who'd been treated for stage 1 or 2 breast cancers.
As to the influence of cruciferous vegetables on breast cancer outcomes, the researchers say the evidence simply isn't there to draw any conclusions about possible benefits.
“It is critically important to stress that these studies were conducted on women who received medical and/or surgical treatment for breast cancer, and that these foods and phytonutrients should not be considered as alternatives to treatment,” said Paller.
