Low-fat dietary pattern and breast cancer mortality by metabolic syndrome components: a secondary analysis of the Women’s Health Initiative (WHI) randomised trial

Background: In the Women’s Health Initiative (WHI) dietary modification (DM) randomised trial, the low-fat dietary intervention reduced deaths from breast cancer (P = 0.02). Extending these findings, secondary analysis examined dietary intervention influence on breast cancer mortality by metabolic syndrome (MS) components. Methods: In total, 48,835 postmenopausal women with no prior breast cancer were randomised to a low-fat dietary intervention or comparison groups. Four MS components were determined at entry in 45,833 participants: (1) high waist circumference, (2) high blood pressure, (3) high cholesterol and (4) diabetes history. Forest plots of hazard ratios (HRs) were generated with P-values for interaction between randomisation groups and MS component score. Primary outcome was death from breast cancer by metabolic syndrome score. Results: HRs and 95% confidence intervals (CI) for dietary intervention influence on death from breast cancer were with no MS components (n = 10,639), HR 1.09, 95% CI 0.63–1.87; with 1–2 MS components (n = 30,948), HR 0.80, 95% CI 0.62–1.02; with 3–4 MS components (n = 4,246), HR 0.31, 95% CI 0.14–0.69 (interaction P = 0.01). Conclusions: While postmenopausal women with 3–4 MS components were at higher risk of death from breast cancer, those randomised to a low-fat dietary intervention more likely had reduction in this risk. Registry: ClinicalTrials.gov (NCT00000611).