The Effect of Viscous Fiber on Glycemic Control in Individuals With Diabetes

Background: Diet high in total dietary fiber content has been recommended for individuals with diabetes mellitus. However, the effect of supplementing diet with viscous fiber such as guar gum, beta glucan, psyllium, konjac, or other viscous fibers on glycemic and insulinemic outcomes in individuals with diabetes mellitus is still controversial.

Objective: To improve the evidence-based guidelines/ recommendations for diabetes mellitus, we will conduct a systematic review and meta-analysis on the effect of viscous fiber supplementation on glycemic control endpoints in individuals with diabetes mellitus.

Design: Cochrane handbook for systematic review of interventions will be used for planning and conducting this meta-analysis. The reporting will follow the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines.

Data sources: MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials will be searched using appropriate pre-determined search terms.

Study selection: All the included trials must be randomized, controlled, with duration of ≥ 3 weeks investigating the effect of supplementing diet with viscous fiber on glycemic control outcomes in individuals with diabetes mellitus. Acute studies, non-randomized, not appropriately controlled studies will be excluded. Both isocaloric and non-isocaloric will be included.

Data extraction: Two independent reviewers will extract information about fiber type, sample size, subject characteristics, dose, follow-up, composition of the background diets, and statistical analyses. Mean±SEM values will be extracted for all outcomes. Standard computation and imputation will be used to derive all missing variance data. Risk of bias and study quality will be assessed using the Cochrane Risk of Bias Tool and the Grading of Recommendations Assessment, Development and Evaluation (GRADE), respectively.

Outcome: This meta-analysis will assess a set of outcomes related to glycemic control in individuals with diabetes mellitus. These outcomes are: (1) glycated hemoglobin A1c (HbA1c), (2) fasting glucose (FG), (3) fasting insulin (FI), (4) fructosmine, and (5) Homeostasis model assessment of insulin resistance (HOMA-IR).

Data synthesis: Pooled analysis will be conducted using the Generic Inverse Variance method. Rand-effects models will be used even in the absence of statistical significant between-study heterogeneity because they yield more conservative summary effect estimates in the presence of residual heterogeneity. Heterogeneity will be assessed using Cochran's Q test and quantified by the I2 statistic. Sensitivity and subgroup analyses will be used to explore sources of heterogeneity. A prioir subgroup analyses include study design, does, fiber type, follow-up (duration), baseline values, study quality, food matrix, and composition of the background diet. The significance of subgroup analyses will be assessed using meta-regression analyses. Publication bias will be assessed using the inspection of funnel plots and application of Egger's and Begg's tests.

Knowledge translation plan: Results will be shared through traditional, national, and international scientific meetings and they will be submitted to high impact factor journals for publication.

Significance: We hope the results of this study will play a role in improving the guidelines/ recommendations for individuals with diabetes mellitus by raising the awareness towards viscous fiber consumption among health providers, patients, and industry. Hopefully, this study will aid in guiding future research in the dietary fiber field.