Phytoestrogens May Not Prevent Breast Cancer
Study Shows Reduction in Breast Cancer Risk Not Seen Even if Started at Early Age
Feb. 4, 2003 -- You may have heard that diets rich in soy that contain phytoestrogen help protect against breast cancer. Now, new research from The Netherlands indicates that diets containing phytoestrogens typically found in Western diets do not show a protective effect.
Researchers studied the association between the consumption of plant-based compounds that have estrogen-like activity, known as phytoestrogens, and breast cancer risk in a study involving more than 15,000 middle-aged and elderly Dutch women.
The main sources of phytoestrogens in the women's diets -- as is the case for most women in the U.S. -- were not soy and flaxseed, but grains, fruit, nuts, and seeds. And like most people eating primarily Western diets, the overall consumption of phytoestrogens was low.
Breast cancer risk among women eating diets containing the highest amounts of these phytoestrogens was similar to those eating lower amounts. The findings are published in the latest issue of the American Journal of Clinical Nutrition.
Most previous studies examining the role of dietary phytoestrogens in breast cancer have focused on soy. Soy researcher Marc Cline, PhD, tells WebMD that the evidence to date remains more than a little contradictory.
Population-based studies seem to overwhelmingly support a protective role for soy phytoestrogens. American women have a breast cancer risk that is as much as six times higher than women who live in Asian countries, where diets rich in soy phytoestrogens are commonly eaten. When Asian women immigrate to the U.S. and adopt more Western diets, they develop a higher risk of breast cancers.
"These are the studies that got people excited about soy," Cline tells WebMD. "But there are a lot of other factors, in addition to diet, that can explain this difference, Asian women typically consume fewer calories overall, they begin to menstruate later in life, they exercise more, eat more vegetables and are thinner than women living in the West."
Studies directly measuring the impact of soy consumption on breast cancer risk show a "weak protective effect", with women who eat soy throughout life and starting at an early age appearing to derive the most benefit, Cline says.