Quantifying the mediating effect of body mass index on the relation between a Mediterranean diet and development of maternal pregnancy complications: the Australian Longitudinal Study on Women's Health.

BACKGROUND: The contribution of body mass index (BMI) to the observed associations between dietary patterns and risk of gestational diabetes mellitus (GDM) and hypertensive disorders of pregnancy (HDP) remains unclear. OBJECTIVE: The objective of this study was to formally quantify the mediating effect of prepregnancy BMI in these associations. DESIGN: Women (aged 25-30 y) participating in the Australian Longitudinal Study on Women's Health were not pregnant at baseline in 2003 and reported ≥1 pregnancy up to 2012. GDM and HDP diagnoses were self-reported for each pregnancy and validated in a subset. A Mediterranean diet score was created by use of a baseline-validated food-frequency questionnaire and dichotomized to reflect low adherence (<25th percentile) and higher adherence (≥25th percentile). A causal inference framework for mediation analysis was used to estimate total, natural direct, and natural indirect effects of the prepregnancy Mediterranean diet on incident GDM and HDP and proportions mediated through prepregnancy BMI. RESULTS: In 3378 women without a history of diabetes, 240 (7.1%) developed GDM. HDP was reported in 273 (8.6%) of 3167 women with no history of hypertension. Low adherence to the Mediterranean diet was associated with higher risk of GDM (OR: 1.35; 95% CI: 1.02, 1.60) and HDP (OR: 1.41; 95% CI: 1.18, 1.56), after adjustment for education, parity, polycystic ovary syndrome, energy intake, and physical activity. Proportions mediated through prepregnancy BMI (per 1-kg/m(2) increase) were 32% and 22% for GDM and HDP, respectively. CONCLUSION: These findings suggest that prepregnancy BMI as a single mediator contributes substantially to the total effects of the prepregnancy Mediterranean diet on GDM and HDP risk.

How do women's diets compare with the new Australian dietary guidelines?

OBJECTIVE: To compare women's diets with recommended intakes from the new Australian Dietary Guidelines (ADG 2013). DESIGN: Cross-sectional study using data from the Australian Longitudinal Study on Women's Health. Diet was assessed using a validated FFQ. SETTING: Two nationally representative age cohorts of Australian women. SUBJECTS: Women in the young cohort (born 1973-1978, aged 31-36 years) and mid-age cohort (born 1946-1951, aged 50-55 years). Women (n 18 226) were categorised into three groups: 'young women' (n 5760), young 'pregnant women' at the time or who had given birth in the 12 months prior to the survey (n 1999) and 'mid-age women' (n 10 467). RESULTS: Less than 2 % of women in all three groups attained the ADG 2013 recommendation of five daily servings of vegetables, with the majority needing more than two additional servings. For young women, less than one-third met recommendations for fruit (32%) and meat and alternatives (28 %), while only a small minority did so for dairy (12 %) and cereals (7 %). Fifty per cent of pregnant women met guidelines for fruit, but low percentages reached guidelines for dairy (22 %), meat and alternatives (10 %) and cereals (2·5 %). For mid-age women, adherence was higher for meat and alternatives (41 %) and cereals (45 %), whereas only 1 % had the suggested dairy intake of four daily servings. CONCLUSIONS: For most women to follow ADG 2013 recommendations would require substantially increased consumption of cereals, vegetables and dairy. Findings have implications for tailoring the dissemination of dietary guidelines for women in different age groups and for pregnant women.