The SNP rs1260326 (P446L) and rs1799884 ( − 30G>A) for the glucokinase regulatory protein (GCKR) and glucokinase (GCK) genes, respectively, have been associated with opposing effects on TAG and glucose concentrations. However, their genetic modulation by diet (dietary patterns or foods) remains to be investigated. We studied 945 high-cardiovascular risk subjects aged 67 (sd 6) years who participated in the PREvención con DIeta MEDiterránea-Valencia Study. Demographic, clinical, biochemical and genetic data were obtained. Adherence to the Mediterranean diet (MD) and food intake were measured by validated questionnaires. Carriers of the L allele of GKCR had significantly higher TAG concentrations (PP: 1·34 (sd 0·05) mmol/l v. PL+LL: 1·54 (sd 0·03) mmol/l; P= 0·014) and LL carriers had lower glucose concentrations (PL+PP: 6·85 (sd 0·08) mmol/l v. LL: 6·40 (sd 0·16) mmol/l; P= 0·032) after multivariate adjustment. Conversely, homozygous subjects for the variant allele (A) in the GCK gene had significantly lower TAG (GG+GA: 1·48 (sd 0·03) mmol/l v. AA: 1·17 (sd 0·18) mmol/l; P= 0·033) and a higher risk of diabetes (OR 3·3, 95 % CI 1·2, 9·2). Combined effects for both SNP increased TAG concentrations by 37 % (P= 0·033). Adherence to the MD modulated the effects of GCKR polymorphism on TAG: subjects with genetic risk had lower TAG (L-allele carriers; PP: 1·48 (sd 0·14) mmol/l v. PL+LL: 1·51 (sd 0·08) mmol/l; P= 0·917) compared with those with a higher adherence. Analysis of the joint effects of the GCKR and individual food items identified significant associations (olive oil (P= 0·035), vegetables (P= 0·012), red meat (P= 0·017), butter (P= 0·039), sweetened carbonated beverages (P= 0·036) and nuts (P= 0·038)). In conclusion, we found that rs1260326 (GCKR) is significantly associated with higher TAG concentrations, but is modulated by adherence to the MD.