(A) Diet-altered behavior (DAB) mediated the effect of diet on gene expression for 24% (n = 1199) of genes for which diet had an effect (differentially expressed genes or DEGs). For 18% of DEGs, gene expression mediated the effect of diet on DAB score. (B) DAB score mediated 23–97% of the total effect of diet on gene expression in 1199 genes (n = 712 Western genes, orange; n = 487 Mediterranean genes, blue). DAB score mediated a greater number of Western genes than Mediterranean genes (p = 1.5 x 10−21) and accounted for a greater portion of the effect size of diet (p = 6.4 x 10−25) in Western genes. (C) In gene-by-gene models of DAB score as a function of diet + gene expression, gene expression mediated 17–51% of the total effect of diet on DAB in 898 genes (n = 523 Western genes; n = 375 Mediterranean genes). Gene expression mediated a greater number of Western genes than Mediterranean genes (p = 4.6 x 10−14), although expression of these genes did not account for more of the effect of diet on DAB score than Mediterranean genes (Mann-Whitney U = 1.0 x 105, p = 0.55).