The Association Between Pre-Pregnancy Excess Weight and the Omega-6/Omega-3 Ratio in Breast Milk: A Directed Acyclic Graph-Based Analysis

Objective: We aimed to evaluate the association between pre-pregnancy excess weight and the adequacy of the ω-6/ω-3 ratio using a directed acyclic graph (DAG) to guide the selection of potential confounders. Methods: We conducted a cross-sectional study with 89 lactating women visiting a breast milk bank in Rio de Janeiro, Brazil. Pre-pregnancy excess weight was assessed using the body mass index according to World Health Organization criteria. ω-6 and ω-3 levels were determined by gas chromatography, and their ratios were calculated and categorized, with a ratio of greater than 10 being considered inadequate in accordance with dietary intake recommendations for these fatty acids. A DAG was constructed to identify a minimally sufficient set of confounders, including maternal age, socioeconomic status, parity, interbirth interval and food consumption patterns. Prevalence ratios were estimated using Poisson regression with robust variance. Results: The mean ω-6/ω-3 ratio was 10.8. Prevalence of inadequate ω-6/ω-3 ratio was higher in women with pre-pregnancy excess weight compared to women with normal pre-pregnancy weight. After adjusting for the confounders identified by the DAG, prevalence of inadequate ω-6/ω-3 ratio was higher among women with pre-pregnancy excess weight (PR = 1.35; 95% CI: 1.02–1.78). Conclusions: Pre-pregnancy excess weight is associated with an unfavorable breast milk lipid profile characterized by an imbalance in the ω-3 to ω-6 essential fatty acid ratio. The use of a DAG-based approach enables parsimonious and theoretically grounded adjustment for potential confounders, contributing to greater robustness of the findings. Our results underscore the importance of nutritional care strategies during the preconception period to promote maternal and child health.