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 (HbA1c). 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, 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 HbA1c 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, I2=75%, P<0.001). Reductions occurred also in fasting glucose, LDL-C, non-HDL-C, apo B, triglycerides, body weight, BMI, and CRP (P<0.05), but not blood insulin, HDL-C, waist circumference, or blood pressure. A positive dose-response gradient was seen for the difference in GL and HbA1c and for absolute dietary GI and SBP (P<0.05). The certainty of evidence was high for the reduction in HbA1c 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, 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.
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Key Points
Previous systematic reviews and meta-analyses have shown that low glycaemic index (GI)/glycaemic load (GL) dietary patterns improve glycaemic control and cardiometabolic risk factors in randomised controlled trials in people at risk for, and with, diabetes and are associated with reduced incidence of diabetes and cardiovascular disease in prospective cohort studies inclusive of people with diabetes. The last comprehensive systematic review and meta-analysis in diabetes was published in 2010, but lacked a GRADE (grading of recommendations assessment, development, and evaluation) assessment for certainty of evidence, and numerous randomised controlled trials have been published after the census for these syntheses. The available evidence suggests that low GI/GL dietary patterns result in small clinically significant reductions in the primary target of glycaemic control HbA1c, and small clinically meaningful improvements in other established cardiometabolic risk factors (blood lipids, body weight, inflammation) in moderately controlled type 1 and type 2 diabetes As these benefits are seen beyond concurrent treatment with hyperglycaemia drugs or insulin, low GI/GL dietary patterns might be especially helpful as addon treatment to help individuals with type 1 and type 2 diabetes achieve their targets for glycaemic control and cardiometabolic risk factors.
Diet and lifestyle remain the cornerstone of the management of diabetes. This synthesis shows that low GI/GL dietary patterns are considered an acceptable and safe dietary strategy that can produce small meaningful reductions in the primary target for glycaemic control in diabetes, HbA1c, fasting glucose, and other established cardiometabolic risk factors. The pooled in trial achieved reduction in HbA1c of −0.31% would meet the threshold of ≥0.3% reduction in HbA1c proposed by the European Medicines Agency as clinically relevant for risk reduction of diabetic complications. Thus low GI/ GL dietary patterns might be an especially helpful lifestyle strategy for those with type 2 diabetes as it might assist in the management of glycaemic control as add-on treatment to hyperglycaemia drugs while at the same time reducing the need for these drugs.
The available evidence shows that low GI/GL dietary patterns might have advantages for reducing the primary target for glycaemic control, HbA1c, as well as fasting glucose and other established cardiometabolic risk factors beyond concurrent treatment with hyperglycaemia drugs or insulin in predominantly adults with moderately controlled type 1 and type 2 diabetes.
Flax provides a wealth of nutrition for the fight against diabetes. Lignans: flaxseed is the richest source of plant lignans, particularly secoisolariciresinol diglucoside (SDG), which is converted by intestinal bacteria to the mammalian lignans secoisolariciresinol (SECO), enterodiol and enterolactone. The approximate SDG content in flaxseed is 375 mg/100 g. Omega-3 fatty acids: flaxseed is the richest plant source of the essential fatty acid a-linolenic acid (ALA). Approximately 55-57% of the fatty acids in flaxseed are ALA. Dietary fibre: flaxseed is a rich source of dietary fibre, including both insoluble and soluble fibre. Flaxseed provides 4 g of fibre in a 2 tablespoon serving.