Association of portfolio diet score with breast cancer risk: insights from a case-control analysis

The Portfolio Diet (PD) is a plant-based dietary approach that has been associated with a reduced risk of cancer-related mortality. The aim of this study was to investigate the relationship between PD score (PDS) and breast cancer (BC) risk in Iranian women, providing insights into the impact of diet on BC risk across different menopausal stages.

The current case-control study included 133 women with newly diagnosed BC and 265 controls without any neoplastic disorders, all of whom were referred to the oncology department of two referral hospitals in Tehran, Iran. A validated semi-quantitative food frequency questionnaire, consisting of 168 food items, was used to gather dietary information. Additionally, odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated to assess the associations of BC with the PDS and its components, using univariate and multivariate logistic regression analysis.

After adjusting for variables in multivariate analysis, a significantly lower association was observed between each unit increase in plant protein intake and the odds of BC in the total population (OR = 0.399, 95% CI: 0.170-0.936). Based on menopausal status, a significant association was found between PDS and the odds of BC in premenopausal women (OR = 0.914, 95% CI: 0.845-0.989). Additionally, in the postmenopausal women, significantly lower odds of BC were observed with each unit increase in plant protein intake in the adjusted model (OR = 0.078, 95% CI: 0.015-0.399).

This study provides novel insights into the protective role of PD against BC, demonstrating that a higher PDS is associated with a significant reduction in BC odds among premenopausal women. Plant protein intake also demonstrated a protective effect against BC in both the overall population and postmenopausal women. These findings highlight the potential benefit of the PD as a preventative dietary strategy against BC, particularly emphasizing the role of plant protein.