A new British prospective study reports that phytoestrogen intake does not affect breast cancer risk, while it can influence risks of prostate and colorectal cancer. Previous studies have not used complete and accurate dietary phytoestrogen data. In the study, medical history, demographic and anthropometric characteristics, and seven-day diet records had been obtained from participants well before any cancer developed. To obtain accurate information concerning phytoestrogen intake, 509 food items were analyzed carefully for isoflavone (genistein, daidzein, glycitein, biochanin A, and formononetin), lignan (secoisolariciresinol and matairesinol), and enterolignan from gut microbial metabolism in animal food sources (equol and enterolactone) content. Using this direct analysis, phytoestrogen values for 10,708 foods were calculated. Phytoestrogen intake was found not to be linked to breast cancer in women or colorectal cancer in men. For women, enterolactone and enterolignan intake both were associated with lower risk of colorectal cancer. However, secoisolariciresinol intake was associated with higher risk of colorectal cancer among women. Enterolignan intake was found to be associated with increased prostate cancer risk, however this risk was reduced when dairy consumption was taken into account. The authors conclude that dietary phytoestrogens may contribute to the risk of colorectal cancer among women and prostate cancer among men.

Previous studies have reported mixed results

This study used the most exhaustive measures of phytoestrogen intake to date, including phytoestrogens derived from animal products. Lignans are found in foods such as flaxseed, rye, and a variety of fruits and vegetables, whereas isoflavones and the enterolignan equol are derived primarily from soy products. The study findings are not consistent with some other studies that have examined the impact of various phytoestrogens on breast cancer risk.