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Evidence summaries

Low Glycaemic Index, or Low Glycaemic Load, Diets for Diabetes Mellitus

Low glycaemic index diets compared to higher glycaemic index diets appear to improve glycaemic control without compromising hypoglycaemic events in less than optimally controlled people with diabetes. Level of evidence: "B"

A Cochrane review [Abstract] 1 included 11 studies (lasting 1 to 12 months) with a total of 402 subjects. 10 studies compared a low glycaemic index (low-GI) diet with a higher glycaemic index diet and 1 study compared the low-GI diet to a diet using measured carbohydrate exchanges. 3 studies had participants with type 1 diabetes, 7 with type 2 diabetes and 1 study had participants with either type 1 or type 2 diabetes. 2 studies involved children, all of whom had type 1 diabetes.

Pooled data from studies reporting glycated haemoglobin A1c (HbA1c) with participants whose glycated haemoglobin was not yet optimised showed that low-GI diets significantly decreased glycated haemoglobin A1c (HbA1c) levels, indicating improved glycaemic control (WMD -0.5 % HbA1c, 95% CI -0.8 to -0.2; 6 studies). 2 studies reported on hypo- or hyperglycaemic events. Hypoglycaemic episodes significantly decreased with low-GI diet compared to high glycaemic index diet (difference of -0.8 episodes per patient per month, P < 0.01; 1 study). In the second study, the control diet was a measured carbohydrate exchange diet in children with type 1 diabetes and there was no difference reported in hypoglycaemic episodes. Proportion of participants reporting more than 15 hyperglycaemic episodes per month was lower for low-GI diet compared to measured carbohydrate exchange diet (35% versus 66%, P = 0.006; 1 study). No study reported on mortality, morbidity or costs.

A meta-analysis 2 included 6 RCTs with type 2 diabetes. In 2 studies, the improvement in HbA1c was higher with low-GI diet (difference -0.5%, 95% CI -0.61% to -0.39%) than with high-cereal fibre diet (difference -0.18%, 95% CI -0.29% to -0.07%); or with low-GI legume diet (difference -0.5%, 95% CI -0.6% to -0.4%) vs high-wheat fibre diet (difference -0.3%, 95% Cl -0.4 to -0.2%). Results in HbA1c favoured low-GI-diet compared to control (mean difference -0.22, 95%CI -0.31 to -0.13, 5 trials, n=574).Comparint the effect of the low-GI diet vs higher-GI diet or control on fasting blood glucose, the meta-analysis favoured the low-GI diet (mean difference -6.59, 95% CI -12.12 to -1.05, 3 trials, n=241). However, the differences were not significant in the sensitivity test (MD -5.42, -12.79to 1.95, p = 0.15).

Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment and lack of reporting on blinding of outcome assessors).

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