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Viscous dietary fiber supplementation decreases HbA1c and fasting blood glucose in patients with type 2 diabetes
Clinical Question
Can a viscous fiber supplement improve blood glucose control in patients with type 2 diabetes?
Bottom line
Adding typical doses of viscous fiber, such as psyllium or guar gum, may lower HbA1c levels an average .58 percentage points (4 mmol/mol) and lower fasting glucose readings an average 15 mg/dL (0.82 mmol/L) in patients with type 2 diabetes. That may not seem like much, but we can only expect lowering of .5 to 2.0 percentage points with oral hypoglycemic medications (https://www.aafp.org/afp/2015/0701/p27.html), and increased fiber may have other benefits. The studies included in this meta-analysis were only a few months in duration and did not address patient-oriented outcomes, but the intervention is easy and inexpensive. 1a
Reference
Study design: Meta-analysis (randomized controlled trials)
Funding: Government
Setting: Various (meta-analysis)
Synopsis
These authors searched 3 databases, including Cochrane CENTRAL, along with reference lists of included trials, and identified 28 randomized trials in any language that enrolled a total of 1394 patients with type 2 diabetes. Two reviewers independently extracted the data and assessed research quality. Most of the studies were short term—2 to 3 months—and used dietary fiber from psyllium, guar gum, or beta-glucan (in various grains and seaweed). Using typical daily doses (eg, 2 teaspoons psyllium daily), fasting glucose dropped an average 15 mg/dL (.82 mmol/L) as compared with nonfiber placebo. Similarly, HbA1c was decreased an average 0.58 percentage points (4 mmol/mol). There didn't seem to be a dose-response effect, though the studies were small and short term. Study quality was moderate and the analysis suffered from significant heterogeneity among the study results. There was no evidence of publication bias.
Reviewer
Allen F. Shaughnessy, PharmD, MMedEd
Professor of Family Medicine
Tufts University
Boston, MA