The insulin resistance phenotype (muscle or liver) interacts with the type of diet to determine changes in disposition index after 2 years of intervention: the CORDIOPREV-DIAB randomised clinical trial

Aims/hypothesis The aim of the study was to determine whether basal insulin resistance (IR) phenotype (muscle and/or liver) determines the effect of long-term consumption of a Mediterranean diet or a low-fat diet on tissue-specific IR and beta cell function. Methods The study was performed in 642 patients included in The effect of an olive oil rich Mediterranean diet on type 2 diabetes mellitus risk and incidence study (CORDIOPREV-DIAB). A total of 327 patients were randomised to a Mediterranean diet (35% fat; 22% from monounsaturated fatty acids) and 315 to a low-fat diet (<28% fat). At baseline, the patients were classified into four phenotypes according to the type of IR: (1) no IR; (2) muscle IR; (3) liver IR; (4) muscle + liver IR. The hepatic insulin resistance index (HIRI), muscular insulin sensitivity index (MISI) and disposition index were analysed at baseline and after 2 years of follow-up. Results At baseline, 322 patients presented no IR, 106 presented muscle IR, 109 presented liver IR, and 105 presented muscle + liver IR. With both dietary interventions, HIRI decreased in all patients (p < 0.001) and MISI increased in muscle IR and muscle + liver IR patients (p < 0.01). Long-term intake of the Mediterranean diet increased the disposition index and insulinogenic index in the muscle IR patients (p = 0.042 and p = 0.044, respectively) and the disposition index in the muscle + liver IR patients (p = 0.048), whereas the low-fat diet increased the disposition index in the liver IR patients (p = 0.017). Conclusions/interpretation Although both diets improve insulin sensitivity, there are differences based on basal IR phenotypes. Moreover, according to insulinogenic and disposition index data, a low-fat diet might be more beneficial to patients with liver IR, whereas patients with muscle IR and muscle + liver IR might benefit more from a Mediterranean diet.