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Maternal underweight and inadequate gestational weight gain (GWG) are problems in Japan. However, increases in food intake aimed at weight gain alone are not sufficient for mother–child health. This study assessed diet quality based on the 3-day dietary records of pregnant women in an urban area of Japan in order to show the importance of evaluating diet quality, using the Nutrient-Rich Food Index 9.3 (NRF9.3), which is one metric based on nutrition profiling, and the Japanese Food Guide Spinning Top (JFGST). After excluding misreporters of energy intake, we stratified women (n = 91) by pre-pregnancy body mass index (BMI) and determined energy intake, diet quality status, and their relationship with GWG. Intakes of carbohydrate-containing staple foods, vegetable dishes, and fruit were insufficient regardless of BMI. Most of the underweight women with inadequate GWG had insufficient energy intake but high diet quality, as assessed by NRF9.3. In contrast, most women who consumed energy within the recommended range had low diet quality and gained weight at inappropriate levels. These results highlight the importance for pregnant Japanese women to maintain diet quality through a nutrient-dense diet, while simultaneously increasing energy intake after evaluation of their individual diet quality.

The maternal diet can potentially influence the life-course health of the child. A poor-quality maternal diet creates nutrient deficiencies and affects immune–metabolic regulation during pregnancy. The nutrient-based overall dietary quality can be assessed using the Nutrient-Rich Food Index 9.3 (NRF9.3), which measures adherence to the national reference daily values of nutrient intake. Pro- and anti-inflammatory nutrient intake can be assessed using the energy-adjusted dietary inflammatory index (E-DII), a comprehensive index of diet-derived inflammatory capacity. Using these indices, we assessed the overall dietary quality and inflammatory potential of pregnant women during mid-gestation in an urban area of Japan (n = 108) and found that there was a strong inverse correlation between the NRF9.3 and E-DII scores. Comparison of the scores among the tertiles of NRF9.3 or E-DII indicated that dietary fiber, vitamin C, vitamin A, and magnesium mainly contributed to the variability of both indices. Intake of vegetables and fruits was positively associated with high NRF9.3 scores and negatively associated with high E-DII scores, after adjustment for maternal age, pre-pregnancy body mass index, and educational level. Consistent with the previous studies that used dietary pattern analysis, this study also demonstrated that vegetables and fruits were the food groups chiefly associated with high dietary quality and low inflammatory potential among pregnant Japanese women.

Mid-to-late gestation is a unique period in which women experience dynamic changes in lipid metabolism. Although the recent intensive epigenome-wide association studies (EWAS) using peripheral leukocytes have revealed that lipid-related traits alter DNA methylation, the influence of pregnancy-induced metabolic changes on the methylation levels of these differentially methylated sites is not well known. In this study, we performed a prospective cohort study of pregnant women (n = 52) using the MassARRAY EpiTYPER assay and analyzed the methylation levels of variably methylated sites, including CPT1A intron 1 and SREBF1 intron 1 CpGs, which were previously verified to be robustly associated with adiposity traits. Although methylation of SREBF1 was associated with body mass index (BMI) and low-density lipoprotein cholesterol at mid-gestation, this association was attenuated at late gestation, which was consistent with the metabolic switch from an anabolic to a catabolic state. However, the BMI association with CPT1A intron 1 methylation appeared to strengthen at late gestation; this association was mediated by pre-pregnancy BMI-dependent change in the leukocyte proportion during mid-to-late gestation. Thus, the methylation of adiposity-related differentially methylated regions was sensitive to metabolic and immunological changes during mid-to-late gestation.