Pregnancy is usually associated with dietary imbalances. We aim to assess the changes in Japanese women's diet and nutritional adequacy before and during pregnancy. In the Japan Environment and Children's Study (JECS), we recruited a large cohort of pregnant women (>100,000) from 15 Japanese communities. We assessed their diet before and during pregnancy by a food frequency questionnaire. The before and during pregnancy intakes of energy, macronutrients, and micronutrients were lower than the recommended level for Japanese women by 1% to 49%. The dietary intakes of pregnant women were lower than their intakes before pregnancy, except for milk, dairy products, and calcium. The daily during pregnancy intake of energy, carbohydrate, fat, protein, folic acid, and iron decreased by 85 kcal, 11.6 g, 2.3 g, 2.8 g, 20 μg, and 0.5 mg than the before pregnancy intake. Pregnant women's declined food and nutrients intakes were moderately correlated to their dietary intakes before pregnancy; the correlation coefficient ranged between 0.47 and 0.67. The inter-individual variability was greater than the intra-individual variability of the dietary intakes. Almost half of the pregnant women remained in the same intake quartile for all nutrients and food groups as before pregnancy. Yet, approximately 10% of pregnant women changed their pregnancy intake by ≥50% (≥2 quartiles up or down) compared to before pregnancy. In conclusion, the study identified low periconceptional dietary intakes among Japanese pregnant women. The low dietary intake of essential nutrients, such as folate, requires revising the Japanese national periconceptional dietary and supplementation guidelines.
Keywords: Japan; epidemiology; maternal diet; pregnancy.