Calculation of DII
The DII score is a comprehensive indicator of daily inflammatory and anti-inflammatory meal contents developed by Shivappa et al.16 The greater the DII score, the more the pro-inflammatory effect of the diet. A higher negative value indicates a more anti-inflammatory diet. The method of calculation of DII in JECS data was previously reported.18 In brief, 30 food parameters were obtained from each participant’s FFQ, including energy, carbohydrate, protein, total fat, alcohol, fibre, cholesterol, saturated fat, monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), fatty acids (n–3 and n–6 FAs), niacin, thiamin, riboflavin, iron, magnesium, zinc, selenium, folic acid, β-carotene, vitamins A, B-12, B-6, C, D, and E, garlic, ginger, and onion. The DII score of each participant was calculated as follows: First, dietary data were linked to a worldwide database that provided a robust estimate of the mean and standard deviation (SD) for each parameter included in the DII.16 The Z score was calculated by subtracting the standard global mean from the reported amount and dividing the result by the SD. The Z scores were not normally distributed (right skewing); thus, the Z score of each value was converted to a centered percentile score. Then, the centered percentile score for each food parameter was multiplied by the respective food parameter effect score (obtained by reviewing a total of 1943 research articles to determine the relationship between food parameters and inflammation, as well as by scoring) to obtain a food parameter-specific DII score, which were all summed to create the overall DII score for each participant. DII = I1∙P1 + I2∙P2 + … + I30∙P30, where I is the food parameter effect score considering the effect of inflammation obtained from reviewed research articles and P is the food-specific centered percentile score derived from food data. The DII minimum/maximum levels in pregnant populations in previous JECS study were reported to range from −6.16 to +5.80.18