Ruminant trans-fatty acids and risk of breast cancer: a systematic review and meta-analysis of observational studies.

Introduction: Ruminant trans-fatty acids, especially cis9, trans11-conjugated linoleic acid (c9,t11-CLA) and trans11-18:1 vaccenic acid (t11-18:1 VA) appear to have anticarcinogenic activity against breast cancer in animal and in vitro experiments. However, the results remain inconsistent. We therefore conducted a systematic review and meta-analysis to assess the association of c9,t11-CLA, and t11-18:1 VA (intake or serum levels) with breast cancer risk.