2.2.2. Dietary Inflammatory Index

We used the data from the EPIC-Norfolk FFQ, as calculated by FETA, to calculate the Dietary Inflammatory Index (DII) [43]. The DII is literature-derived, using a large-scale meta-analytic strategy to compute averaged inflammatory/anti-inflammatory effects for individual nutrient parameters that have sufficient evidence to capture their effect on inflammatory markers. The DII has been validated against several peripheral markers of inflammation, including interleukin (IL)-6 [53,54] and tumour necrosis factor (TNF)-α [55].

In the current study, the following 25 food and nutrient parameters were used: alcohol, β-carotene, total carbohydrate, cholesterol, fibre, iron, folate, energy, magnesium, niacin (vitamin B3), total protein, retinol (vitamin A), riboflavin (vitamin B2), selenium, thiamine (vitamin B1), vitamin B12, vitamin B6, vitamin C, vitamin D, vitamin E, total fat, MUFA, PUFA, and SFA. For full details, on the steps to calculate the DII® [43], see Shivappa et al. [43]. Briefly, values of the nutrients listed above are standardised into a *z* score by subtracting the mean from the global database and dividing this by the standard deviation from the global database (global daily mean intakes and standard deviations listed in Shivappa et al. [43] for each nutrient). To minimise the effect of 'right skewing' this value is converted into a percentile score. To achieve a symmetrical distribution with values centred on 0 (null) and bounded between −1 (maximally anti-inflammatory) and +1 (maximally pro-inflammatory), each percentile score is then doubled and '1' is subtracted. The centred percentile value for each food parameter is then multiplied by its respective 'overall food parameter-specific inflammatory effect score', listed in Shivappa et al. [43], to obtain the 'food parameter-specific DII score'. Finally, all of the 'food parameter-specific DII scores' for the available nutrients are summed to create the 'overall DII score' for an individual. A higher DII score indicates greater inflammatory potential of an individual's diet. The DII score could range from +7.98 (maximally pro-inflammatory) to −8.87 (maximally antiinflammatory) when calculated from all 45 food parameters for which the creators of the DII calculated an inflammatory score [56].
