Objective: Treatment of type 2 diabetes includes pharmacologic and lifestyle modification such as dietary change. The use of the Glycemic Index (GI) to guide food choice has been advocated, although the effectiveness of this dietary strategy in people with type 2 diabetes has had mixed success. Our objective was to investigate daylong glycemic responses to diets differing in GI using continuous glucose monitoring in people with type 2 diabetes.
Methods: A randomized crossover trial in 22 adults aged 18 to 75 years diagnosed with type 2 diabetes and without major co-morbidities. Lower and higher GI diets were consumed over a five-day period with food supplied to participants. Diet and physical activity were standardized and medication was maintained for the study period. Main outcomes using a Continuous Glucose Monitoring System (CGMS) were mean 24-hour glucose, three-hour incremental postprandial glycemia (iAUC), total day-long glycemia (AUC), and 48-hour glycemic variability assessed as Mean Amplitude of Glycemic Excursion (MAGE).
Results: Complete CGMS data for 18 participants were obtained. The between-treatment difference in GI was 13 GI units (P<0.01). Between low- and high-GI diets, no difference in three-hour iAUC (mmol/L•min) following breakfast (367 vs. 390, P=0.69), lunch (252 vs. 317, P=0.16) or dinner (216 vs. 263, P=0.32) was observed. No difference in mean 24-hour glucose (6.62 vs. 6.31 mmol/L, P=0.31), total day-long glycemia (8,906 vs. 8,786 mmol/ L•min, P=0.82) or MAGE (3.7 vs. 3.9 mmol/L, P=0.61) were observed between diets.
Conclusions: Differences in dietary GI were not predictive of improvement in within-day markers of glycemic control in people with type 2 diabetes. These findings are reflective of ongoing difficulties in translating laboratorygenerated GI values of individual foods to glycemic improvement in the whole of diet setting.