Abstract
BACKGROUND: Some dietary recommendations continue to recommend carbohydrate restriction as a cornerstone of dietary advice for people with diabetes. PURPOSE: We compared the cardiometabolic effects of diets higher in both fiber and carbohydrate with lower carbohydrate lower fiber diets in type 1 or type 2 diabetes. DATA SOURCES: MEDLINE, Embase, and the Cochrane Database of Systematic Reviews up to June 24, 2024, with additional hand searching. STUDY SELECTION: Randomized controlled trials in which both dietary fiber and carbohydrate amount had been modified were identified from source evidence syntheses on carbohydrate amount in people with diabetes. DATA EXTRACTION: Two reviewers independently. DATA SYNTHESIS: Ten eligible trials including 499 participants with diabetes (98% with T2) were identified from the potentially eligible 828 trials included in existing evidence syntheses. Pooled findings indicate that higher fiber higher carbohydrate diets reduced HbA1c (mean difference [MD] -0.50% [95% confidence interval -0.99 to -0.02]), fasting insulin (MD -0.99 μIU/mL [-1.83 to -0.15]), total cholesterol (MD -0.16 mmol/L [-0.27 to -0.05]) and low-density lipoprotein cholesterol (MD -0.16 mmol/L (-0.31 to -0.01) when compared with lower carbohydrate lower fiber diets. Trials with larger differences in fiber and carbohydrate intakes between interventions reported greater reductions. Certainty of evidence for these outcomes was moderate or high, with most outcomes downgraded due to heterogeneity unexplained by any single variable. LIMITATIONS: Our predefined scope excluded trials with co-interventions such as energy restriction, which may have provided addition information. CONCLUSIONS: Findings indicate the greater importance of promoting dietary fiber intakes, and the relative unimportance of carbohydrate amount in recommendations for people with diabetes.