Dietary soy intake and breast cancer risk

To conduct a metasynthesis of the literature on human studies of the relationship between dietary soy intake and breast cancer risk.

Publications in English reporting human studies were searched with the terms soy and breast cancer, using Ovid, PubMed, and EBSCO databases. Only human studies investigating the relationship of soy intake to breast cancer development in women published from January 1997 through June 2008 were included in the review.

A total of 364 publications were located; 18 of the studies met the inclusion criteria and 18 additional studies were located through other publications identified in the search. Because four articles reported on the same two studies, a total of 34 studies were included in the review.

The naturally occurring dietary intake of soy food or its components appears safe for women without breast cancer; however, the safety of high supplements of soy or its components is less certain.

Nurses should become more knowledgeable about soy foods and supplements and include soy intake in dietary assessments. Nurses caring for women at high risk for or with a history of breast cancer should confer with dietitians on current practice recommendations. Women with health issues should avoid initiating high intake of soy dietary supplements until the possible effects are better understood.