Reply to: Letter to the editor-dietary inflammatory index and psychological disorders

Abstract

We thank Kawada for his interest in reading our work on the asso- ciation between inflammatory potential of the diet and psychological disorders [1]. As underlined inprevious studies,the inflammatory po- tential of the diet can be examined by considering the anti- and pro- inflammatorypropertiesofnutrientsandfoods.InthepaperofClinical Nutrition[1],weconstructednutrient-baseddietaryinflammatoryin- dex (DII) and examined the association of DII and psychological disor- ders. In another study [2], which Kawada has pointed out, we developedanempirically-derivedfood-basedDII(FDII)andexamined its association with psychological disorders. Although these two indices examine the inflammatory potential of the diet, their compo- nentsandconstructionmethodaredifferent,asmentionedintherele- vant papers [1,2]. In both studies, we found that adherence to a pro- inflammatory diet was associated with increased riskof psychological disorders.However,nutrient-basedDIImightbedifferentlyassociated withpsychologicaldisorders becauseof theinteractionsamongnutri- ents and their synergistic effects on each other in the gastrointestinal lumen.Comparingourpublicationsonnutrient-basedandfood-based dietary inflammatory index, we found that nutrient-based DII was strongly associated with depression, anxiety and psychological distress than food-based one. Different effect sizes from these two studies are expected, because construction method of nutrient- based DII and food-based DII are completely different. It seems that the greater effect sizes of nutrient-based DII, compared with food- based DII, might be due to the synergistic effects of nutrients on each other in the gastrointestinal lumen. It must be kept in mind that DII calculation was based on nutri- ents that are associated with inflammation. On the other hand, inflammation is a major contributing factor to psychological disor- ders [3]. With regards to the Mediterranean dietary pattern, which was inversely associated with psychological disorders in our dataset [4], Kawada suggested that the association of DII with psychological disorders might be suppressed by Mediterranean diet. However, components of DII and Mediterranean diet are not the same. In orig- inal scoring of DII, 45 food parameters were considered. In our study, we had 29 food parameters for DII calculation due to lack of data on some parameters, of them, 9 were pro-inflammatory and 20 were anti-inflammatory parameters. Although, none of these parameters were separately considered in the scoring method of Mediterranean diet, the anti-inflammatory nutrients we had in DII might be involved in the effect of Mediterranean diet. This has clearly been shown by earlier studies that the Mediterranean diet cools down inflammation [5] and therefore, psychological disorders [4]. DII con- siders the inflammatory potential of the whole diet, which is composed of both pro- and anti-inflammatory nutrients, therefore, one should not conclude that the association of DII with psycholog- ical disorders is attenuated with Mediterranean diet because anti- inflammatory nutrients of Mediterranean diet have been taken into account in the DII calculation