Effects of hypocaloric diets with different glycemic indexes on endothelial function and glycemic variability in overweight and in obese adult patients at increased cardiovascular risk

Background & aims: The role of glycemic index of the diet in glucose control and cardiovascular prevention is still not clear. The aim of this study was to determine the effects of hypocaloric diets with different glycemic indexes and glycemic loads on endothelial function and glycemic variability in nondiabetic participants at increased cardiovascular risk. Methods: Forty nondiabetic obese participants were randomly assigned to a three-month treatment with either a low glycemic index (LGI; n ¼ 19) or high glycemic index (HGI; n ¼ 21) hypocaloric diet with similar macronutrient and fiber content. Endothelial function was measured as flow-mediated dilatation (FMD) of the brachial artery before and after dieting. In addition, 48-h continuous subcutaneous glucose monitoring was done before and after dieting in a subgroup of 24 participants. Results: The amount of weight loss after dieting was similar in both groups. The glycemic index of the diet significantly influenced the FMD (P < 0.005). In particular, the change of FMD was 2.3 2.6% following the LGI diet, and 0.9 3.6% after the HGI diet (P < 0.005). The mean 48-h glycemia decreased significantly after dietary treatment (P< 0.05), but no significant effect of the glycemic index of the diet on results was observed. The glycemic index of the diet significantly influenced the 48-h glycemic variability measured as coefficient of variability (CV%; P< 0.001). The CV% decreased after the LGI diet (from 23.5 to 20.0%) and increased after the HGI diet (from 23.6 to 26.6%). The change in percentage of FMD was inversely correlated with the change in the 48-h glycemic CV% (r¼ 0.45; P < 0.05). Conclusions: Endothelial function and glycemic variability ameliorate in association with the adherence to an LGI hypocaloric diet in nondiabetic obese persons. Clinical trial registration number: ISRCTN56834511.