Low Glycemic Index Dietary Pattern Improves HbA1c in Patients with Diabetes

John L Sievenpiper, MD, PhD

Although previous analysis has shown low glycemic index (GI) and low glycemic load (GL) dietary patterns improve glycemic control and cardiometabolic risk factors in people at risk of diabetes, clinical practice guidelines from the European Association for the Study of Diabetes (EASD) were last updated in 2004.

In order to update clinical practice guidelines for nutrition treatment, a systematic review and meta-analysis summarized the effect of low GI/GL dietary patterns on glycemic control in patients with type 1 and type 2 diabetes.

The team, led by John L Sievenpiper, MD, PhD, Department of Nutritional Sciences, Temerty Faculty of Medicine, University of Toronto, found low GI/GL dietary patterns had small clinically significant reduction in the primary target of HbA1c and small clinically meaningful improvement in other cardiometabolic risk factors in patients with moderately controlled diabetes.

Methods

Investigators searched databases (Medcline, Embase, and the Cochrane Central Register of Controlled Trials) until May 2021, including RCTs with follow-up of ≥3 weeks investigating the effect of low GI/GL diet on glycemic control in patients with type 1 or type 2 diabetes.

A team of 2 investigators independently review data from each report, using a standardized form consisting of sample size, study design, GL/GL dose during intervention and control, follow-up, and outcome data.

The primary outcome was difference in glycated hemoglobin (HbA1c). Secondary outcomes included fasting glucose levels, low density lipoprotein (LDL-C), high density lipoprotein (HDL-C), adiposity, blood pressure and inflammation (C - reactive protein).

Data on the mean difference between intervention and control arms were extracted and then used as the basis for analysis in each trial comparison.

Further, the team used the GRADE (grading of recommendations assessment, development, and evaluation) approach to assess overall certainty of evidence, in which it was graded as high, moderate, low, or very low certainty.

Results

Investigators included a total of 27 reports containing data for 29 trial comparisons in the final analyses, with 1617 participants.

Trials had a median follow-up of 12 weeks, with an equal distribution of men and most patients (90%) with type 2 diabetes. Further, most patients were middle-aged (median age 56 years), overweight or obese (median BMI 31), with moderate glycemic (median baseline HbA1c 7.7%) treated with hyperglycemia or insulin.

For the primary outcome, investigators observed in those with mixed type 1 and type 2 diabetes, low GI/GL dietary patterns resulted in a reduction in HbA1c, compared with control diets with a mean difference of −0.31 (95% CI −0.42 to −0.19%), P <0.001; substantial heterogeneity, I2=75%, P <0.001).

In addition, investigators observed reductions from low GI/GL diets in non-HDL-C (mean difference -0.20 mmol/L; 95% CI, -0.33 to -0.07, P = .002), LDL-C (−0.17 mmol/L; 95% CI, −0.25 to −0.08, P <.001), apo B (−0.05 g/L; 95% CI, −0.09 to −0.01, P = .03), triglycerides (−0.09 mmol/L; 95% CI, −0.17 to −0.01, P = 0.04), BMI (−0.38; 95% CI, −0.64 to −0.13, P = .003, and CRP (−0.41 mg/L; 95% CI, −0.78 to −0.04, P = .03).

However, no reductions were observed in blood in HDL-C, waist circumference, or blood pressure.

Conclusion

Investigators concluded this analysis supported recommendation for the use of low GI/GL dietary patterns in the management of diabetes, with advantages in reducing HbA1c, as well as other cardiometabolic risk factors.

“The main source of uncertainty, imprecision, should be considered by further large high quality randomized controlled trials, which target lower GI/GL diets with bigger differences between test and control,” investigators wrote.

The study, “Effect of low glycaemic index or load dietary patterns on glycaemic control and cardiometabolic risk factors in diabetes: systematic review and meta-analysis of randomised controlled trials”, was published online in BMJ.