Differential Glycemic Effects of Low- versus High-Glycemic Index Mediterranean-Style Eating Patterns in Adults at Risk for Type 2 Diabetes: The MEDGI-Carb Randomized Controlled Trial

Abstract

A Mediterranean-style healthy eating pattern (MED-HEP) supports metabolic health, but the utility of including low-glycemic index (GI) foods to minimize postprandial glucose excursions remain unclear. Therefore, we investigated the relative contribution of GI towards improvements in postprandial glycemia and glycemic variability after adopting a MED-HEP. We conducted a randomized, controlled dietary intervention, comparing high- versus low-GI diets in a multi-national (Italy, Sweden, and the United States) sample of adults at risk for type 2 diabetes. For 12 weeks, participants consumed either a low-GI or high-GI MED-HEP. We assessed postprandial plasma glucose and insulin responses to high- or low-GI meals, and daily glycemic variability via continuous glucose monitoring at baseline and post-intervention. One hundred sixty adults (86 females, 74 males; aged 55 ± 11 y, BMI 31 ± 3 kg/m2, mean ± SD) with ≥two metabolic syndrome traits completed the intervention. Postprandial insulin concentrations were greater after the high-GI versus the low-GI test meals at baseline (p = 0.004), but not post-intervention (p = 0.17). Postprandial glucose after the high-GI test meal increased post-intervention, being significantly higher than that after the low-GI test meal (35%, p < 0.001). Average daily glucose concentrations decreased in both groups post-intervention. Indices of 24-h glycemic variability were reduced in the low-GI group as compared to baseline and the high-GI intervention group. These findings suggest that low-GI foods may be an important feature within a MED-HEP.

Keywords: Mediterranean diet; continuous glucose monitoring; glycemic variability; impaired glycemic control; insulinemia; meal glucose tolerance test; metabolic health; metabolic risk factors; metabolic syndrome; oral glucose tolerance test.

Figure 1

CONSORT participant flow diagram.

Figure 2

Insulin (a) and glucose (b) responses to a low-GI and high-GI 8-h meal glucose tolerance test at baseline and after a 12-week dietary intervention. Inset bar graphs display average postprandial insulin and glucose elevations above fasting concentrations over the 8-h period. Data are means ± SEM. * Statistically significant, p < 0.05. ns, no significance.

Figure 3

24-h continuous glucose monitor-derived measures of glycemic variability at baseline and after a 12-week dietary intervention. (a) Average 24-h glucose concentration, (b) standard deviation (SD), (c) continuous overall net glycemic action (CONGA), (d) lability index, (e) mean amplitude of glucose excursions (MAGE), and (f) mean absolute glucose (MAG). Presented data are means ± SEM. * Statistically significant, p < 0.05. ns, no significance.