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
Authors: Chiavaroli Laura , Lee Danielle , Ahmed Amna , Cheung Annette , Khan Tauseef A , Blanco Sonia , Mejia  , Mirrahimi Arash , Jenkins David J A , Livesey Geoffrey , Wolever Thomas M S , Rahelić Dario , Kahleová Hana , Salas-Salvadó Jordi , Kendall Cyril W C , Sievenpiper John L 
Published: August 2021

Abstract

Objective
To inform the update of the European Association for the Study of Diabetes clinical practice guidelines for nutrition therapy.

Design
Systematic review and meta-analysis of randomised controlled trials.

Data sources
Medline, Embase, and the Cochrane Library searched up to 13 May 2021.

Eligibility criteria for selecting studies
Randomised controlled trials of three or more weeks investigating the effect of diets with low glycaemic index (GI)/glycaemic load (GL) in diabetes.

Outcome and measures

The primary outcome was glycated haemoglobin (HbA
1c
). Secondary outcomes included other markers of glycaemic control (fasting glucose, fasting insulin); blood lipids (low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), non-HDL-C, apo B, triglycerides); adiposity (body weight, BMI (body mass index), waist circumference), blood pressure (systolic blood pressure (SBP) and diastolic blood pressure (DBP)), and inflammation (C reactive protein (CRP)).

Data extraction and synthesis
Two independent reviewers extracted data and assessed risk of bias. Data were pooled by random effects models. GRADE (grading of recommendations assessment, development, and evaluation) was used to assess the certainty of evidence.

Results

29 trial comparisons were identified in 1617 participants with type 1 and 2 diabetes who were predominantly middle aged, overweight, or obese with moderately controlled type 2 diabetes treated by hyperglycaemia drugs or insulin. Low GI/GL dietary patterns reduced HbA
1c
in comparison with higher GI/GL control diets (mean difference −0.31% (95% confidence interval −0.42 to −0.19%), P<0.001; substantial heterogeneity, I
2
=75%, P<0.001). Reductions occurred also in fasting glucose, LDL-C, non-HDL-C, apo B, triglycerides, body weight, BMI, systolic blood pressure (dose-response), and CRP (P<0.05), but not blood insulin, HDL-C, waist circumference, or diastolic blood pressure. A positive dose-response gradient was seen for the difference in GL and HbA
1c
and for absolute dietary GI and SBP (P<0.05). The certainty of evidence was high for the reduction in HbA
1c
and moderate for most secondary outcomes, with downgrades due mainly to imprecision.

Conclusions
This synthesis suggests that low GI/GL dietary patterns result in small important improvements in established targets of glycaemic control, blood lipids, adiposity, blood pressure, and inflammation beyond concurrent treatment with hyperglycaemia drugs or insulin, predominantly in adults with moderately controlled type 1 and type 2 diabetes. The available evidence provides a good indication of the likely benefit in this population.

Study registration

ClinicalTrials.gov
NCT04045938
.