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