CRD summary

The review concluded that dietary fibre can reduce glycosylated haemoglobin and fasting blood glucose in patients with type 2 diabetes mellitus. Potential for biases and the differences between trials mean that a degree of caution is required when interpreting the authors’ conclusions. The authors’ call for further research appears warranted.

Authors' objectives

To determine whether an increase in dietary fibre affects glycosylated haemoglobin and fasting blood glucose in patients with type 2 diabetes mellitus.

Searching

PubMed, CINAHL and Cochrane Central Register of Controlled Trials (CENTRAL) were searched from January 1980 to February 2011 for articles in English. Search terms were reported. Reference lists of retrieved articles were searched.

Study selection

Randomised controlled trials (RCTs) that involved an increase in dietary fibre as an intervention versus control in patients with type 2 diabetes mellitus were eligible for inclusion. Trials had to report on glycosylated haemoglobin or fasting blood glucose as an outcome. Trials in which two types of dietary fibre were compared or where diets were dissimilar between groups were excluded.

The included trials studied various forms of soluble and insoluble fibre (including cereal, guar gum, beet fibre and wheat fibre). The increase in dietary fibre compared with the control group ranged from 4g to 40g. Where reported, the mean age of patients ranged from 51.9 to 69.1 years. Trials were published between 1984 and 2007. More than half of the trials were randomised cross-over design.

The authors did not state how many reviewers undertook study selection.

Assessment of study quality

Quality assessment was undertaken using the GRADE tool to classify trial quality as high, moderate, low or very low.

The authors did not state how many reviewers undertook quality assessment.

Data extraction

Mean and standard deviation data were extracted on glycosylated haemoglobin or fasting blood glucose (standardised to mmol/L). Data on standard errors were converted to standard deviations.

The authors did not state how many reviewers extracted the data.

Methods of synthesis

A fixed-effect meta-analysis was undertaken to calculate pooled mean differences, with 95% confidence intervals (CIs). Statistical heterogeneity was assessed using the Χ² and Ι² statistics. A random-effects meta-analysis was used where there was evidence of significant statistical heterogeneity. Publication bias was assessed using funnel plots.

Results of the review

Fifteen RCTs were included (484 patients, range 10 to 58). Eleven trials were graded as high quality and four trials as moderate quality. The length of follow-up ranged from three to 12 weeks.

Compared with control, dietary fibre was associated with a statistically significantly lower fasting blood glucose (mean difference -0.85mml/L, 95% CI -1.25 to -0.46; 13 RCTs; Ι²=5%) and a reduced glycosylated haemoglobin (mean difference -0.26, 95% CI -0.51 to -0.02; 10 RCTs; Ι²=21%).

There was evidence of publication bias with the glycosylated haemoglobin outcome.

Authors' conclusions

Dietary fibre can reduce glycosylated haemoglobin and fasting blood glucose in patients with type 2 diabetes mellitus.

CRD commentary

Inclusion criteria for the review were clearly defined. Three relevant data sources were searched. There may have been the potential for language bias as only articles in English were included. Publication bias was assessed and was detected for one of the outcomes. The authors did not state whether they made any attempts to reduce reviewer error and bias during the review. Quality assessment indicated that all of the trials were of moderate to high quality; individual quality items were not reported and this made the quality assessment difficult to interpret. There were large differences in the amount and type of dietary fibre used in the studies. Data were pooled using appropriate meta-analysis techniques. Statistical heterogeneity was reported. The authors noted that the reduction in glycosylated haemoglobin may not have been clinically significant.

Potential for biases and the differences between trials mean that a degree of caution is required when interpreting the authors’ conclusions. The authors’ call for further research appears warranted.

Implications of the review for practice and research

Practice: The authors stated that increasing dietary fibre should be encouraged as a disease management strategy for patients with type 2 diabetes.

Research: The authors stated that further studies of more than 12 weeks were warranted to test the effect of fibre on glycosylated haemoglobin. Studies with larger doses of fibre were warranted to help support current recommendations for dietary fibre intake in type 2 diabetes.

Funding

None.

Bibliographic details

Post RE, Mainous AG, King DE, Simpson KN. Dietary fiber for the treatment of type 2 diabetes mellitus: a meta-analysis. Journal of the American Board of Family Medicine 2012; 25(1): 16-23. [PubMed: 22218620]

Original Paper URL

http://www.jabfm.org/content/25/1/16.abstract

Indexing Status

Subject indexing assigned by NLM

MeSH

Aged; Blood Glucose /analysis; Diabetes Mellitus, Type 2 /diet therapy /physiopathology; Dietary Fiber /therapeutic use; Female; Hemoglobin A, Glycosylated /analysis; Humans; Male; Middle Aged; Outcome Assessment (Health Care)

AccessionNumber

12012002906

Database entry date

06/11/2012

Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.