AbstractEvidence from epidemiological studies suggests that dietary fiber, as well as fat, has the potential for affecting breast cancer risk. Fiber may have a protective role because of its influence on estrogen metabolism and excretion or because of the endocrine effects of the lignans, a family of compounds formed in the intestine from fiber‐associated precursors. Future research should include additional mechanistic studies and dietary intervention trials in groups of women that have a high risk of breast cancer.