Can viscous fiber lower glycemic markers in type 2 diabetes?
The first meta-analysis to focus on viscous dietary fiber in T2D suggests a potential role for this supplement in improving glycemic control.
PRACTICE CHANGER
Unless contraindicated, recommend viscous fiber supplementation to your patients with type 2 diabetes (T2D), in addition to the usual evidence-based standards of care, to improve markers of glycemic control.
STRENGTH OF RECOMMENDATION
C: Based on a meta-analysis and systematic review of 28 randomized controlled trials, without discussion of patient-oriented outcomes.1
Jovanovski E, Khayyat R, Zurbau A, et al. Should viscous fiber supplements be considered in diabetes control? Results from a systematic review and meta-analysis of randomized controlled trials. Diabetes Care. 2019;42:755-766. Published correction appears in Diabetes Care. 2019;42:1604.
The study found moderate-grade evidence that, when added to standard of care, viscous fiber supplementation reduced hemoglobin A1C (MD = –0.58%; 95% CI, –0.88 to –0.28; P = .0002; I2 = 91%), fasting glucose (MD = –14.8 mg/dL; 95% CI, –23.8 to –5.58; P = .001; I2 = 92%), and HOMA-IR (MD = –1.89; 95% CI, –3.45 to –0.33; P = .02; I2 = 94%) compared with control. The effect on hemoglobin A1C exceeds the ≥ 0.3% threshold established by the US Food and Drug Administration for new antihyperglycemic drug development. There was no significant effect on fasting insulin or fructosamine, although the sample size for fructosamine was small. No significant evidence of a dose-dependent response effect was found. The studies had substantial heterogeneity. No evaluation of potential or real harm was noted in the analysis.
WHAT’S NEW
Potential glycemic benefit without large dietary increase
The glucose-lowering effects of increased fiber intake have often been hypothesized, but this meta-analysis is the first to focus specifically on the effect of viscous fiber supplements in patients with T2D. Prior meta-analyses, including those cited in the 2019 ADA recommendations mentioned above, included primarily whole-food dietary sources of fiber in the treatment arms and generally had more modest effects on outcomes.4,6,7
By focusing on viscous fiber supplements, this study isolated the effect of these supplements vs fiber-rich dietary changes. It illustrates a greater potential benefit with supplements than whole-food dietary sources of fiber, and at a lower dose of fiber than was seen in prior studies without requiring substantial increases in caloric intake. Viscous fiber supplementation is a potential adjunct to the usual evidence-based standards of care for glycemic control in patients with T2D.
CAVEATS
Limited study durations may raise uncertainty about long-term benefits
This meta-analysis does have its limitations. The heterogeneity among the studies analyzed makes it difficult to establish a single recommendation regarding dose, type, and brand of fiber to be used. Only 11 of the 28 studies lasted longer than 12 weeks, with a median duration of 8 weeks, making any long-term effects on hemoglobin A1C unknown. No adverse effects or reactions were described to evaluate safety and tolerability of the viscous fiber supplementation. No patient-oriented outcomes were reported.
CHALLENGES TO IMPLEMENTATION
Patients may not be eager to supplement with viscous fiber
The biggest challenge to implementation is patient compliance. Some forms of supplemental fiber are less palatable than others and may cause unpleasant gastrointestinal adverse effects, which may be an impediment for some patients. Cost may also be an issue for some patients. Diabetes medications can be expensive; however, they are often covered, at least partially, by medical insurance. Over-the-counter supplements are unlikely to be covered for most patients.
ACKNOWLEDGEMENT
The PURLs Surveillance System was supported in part by Grant Number UL1RR024999 from the National Center for Research Resources, a Clinical Translational Science Award to the University of Chicago. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Center for Research Resources or the National Institutes of Health.
