Peri-conception maternal nutrition and its association with offspring sex: a prospective cohort study using the Japan Environment and Children’s Study data

The impact of maternal nutrition during the peri-conception period on offspring sex remains unclear. Therefore, this study aimed to explore the association between maternal nutritional intake around conception and offspring sex. Data were collected from the Japan Environment and Children's Study, which enrolled 97,510 mother-child pairs. The effect of maternal intake of fats, proteins, and fatty acids on offspring sex was analyzed, adjusting for maternal demographics and lifestyle factors. Overall, maternal intake of total fatty acids, saturated fatty acids (SFAs), polyunsaturated fatty acids (PUFAs), <i>n-</i>3 PUFA, <i>n</i>-6 PUFA, and protein and the ratios of <i>n</i>-6/<i>n</i>-3 and SFA/energy showed no consistent associations with offspring sex.However, further analyses revealed notable patterns related to maternal age and energy intake. Among mothers with high energy intake (≥4,000 kcal/day), higher residual protein intake was associated with increased odds of having a male child (aOR, 1.87; 95% CI, 1.17-2.98). In mothers aged under 20 years, increased n-3 PUFA intake was linked to higher odds of male births, while a higher <i>n</i>-6/<i>n</i>-3 ratio was associated with lower odds of male births. Additionally, among mothers aged 20-35 years, higher n-3 PUFA intake was associated with decreased odds of having a male child (aOR, 0.89; 95% CI, 0.82-0.98).These findings indicate that while no consistent overall relationship was observed, certain maternal nutritional patterns may influence offspring sex, highlighting the need for further research on maternal diet and reproductive outcomes.