This review concluded that there was a significant reduction of serum triacylglycerol concentrations with dietary inulin-type fructans intake. However, given that insufficient details were provided to determine the presence of clinical heterogeneity, and selection bias and trial validity assessment were not reported, the author's conclusion should be interpreted with caution as it may not be reliable.

To quantify the effects of dietary inulin and oligofructose on serum triacylglycerols.

PubMed and SCOPUS were searched for articles in English, Italian, Spanish or French, published from January 1996 to June 2006. Search terms were reported. The reference lists of four reviews were also searched.

Randomised controlled trials (RCTs) of the effects of dietary inulin-type fructans (inulin and oligofructose) on serum lipid concentrations were eligible for inclusion. Trials had to have a sequential, parallel or crossover design. Eligible trials also had to specify the type and amount of inulin-type dietary fructans used, and to provide outcome measures of serum triacylglycerol concentrations.

The included trials evaluated oligofructose and inulin of different chain lengths. The average amount of substance, given as sweetener or powder, was 14g daily for oligofructose (range 8g to 20g) and 14.2g daily for inulin (range 4g to 34g). The median duration of the trials was 28 days (range 21 to 64). The patients in the included trials were men and women who were healthy individuals (46%), had hypercholesterolaemia or hypertriglyceridaemia (39%), type II diabetes (9.3%), or non-alcoholic fatty liver disease (2%). In the majority of the trials, the participants were used as their own control.

The author did not specify how the papers were selected for the review, or how many reviewers performed the selection.

The author did not state that he assessed validity.

Data on the initial and final values of triacylglycerol concentrations (mmol/L) were extracted for intervention and control groups to calculate the mean differences. Where data were provided in non-SI format, the units were multiplied by 0.0113 to calculate mmol/L. For trials reporting multiple time points, only endpoints for the longest duration were used.

The author did not state how many reviewers performed the data extraction.

The pooled standardised mean difference and 95% confidence intervals (CI) were calculated using fixed-effect and random-effects models; only results of the random-effects estimate are presented. Statistical heterogeneity was assessed using the χ² and I² tests. Publication bias was assessed using a funnel plot.

Fifteen RCTs were included in the review. There were 323 participants with each condition (intervention or control), including 290 participants for 16 comparisons. The sample sizes of the trials varied from seven to 66; 10 trials had less than 15 subjects. Sixteen RCTs were entered in the meta-analysis. This was possible as one trial, that used a Latin square design with cross-over comparisons among three intervention arms, was entered as two separate trials. Three trials had a sequential design (n=47 participants); two trials had a parallel design (n=66 participants); and 10 trials had a cross-over design (n=198 participants).

Inulin-type fructans significantly reduced serum triacylglycerols by -0.17 mmol/L (95% CI: -0.33 to -0.01) compared to placebo. A χ² test showed no evidence of statistical heterogeneity (p=0.55). The author stated that no significant publication bias was shown by a funnel plot on the effect of total cholesterol by standard error (data not shown).

The intake of dietary inulin-type fructans (inulin and oligofructose) was associated with a significant decrease in serum triacylglycerol concentrations.

The review addressed a well-defined question in terms of interventions, outcomes, study design and participants. The author searched two relevant databases and included trials published in multiple languages, but it was possible that language bias may have been introduced. Publication bias was assessed and no evidence was found (although data were not presented). The author did not report whether validity assessment was performed, and did not report if any attempt was made to reduce bias during study selection and data extraction; this made the synthesis of the results unreliable.

Pooling appeared to have been appropriate statistically, but one of the trials was counted twice, which might have spuriously increased the effect size in favour of the intervention group. Also, few patient and trial details were reported; as some patients were healthy and some had health conditions, it was unclear whether they were comparable at baseline, suggesting a possible clinical heterogeneity among trials. The confidence interval of most trials crossed zero, and some confidence intervals appeared to be wide (although confidence interval ranges were not reported); only five of the included trials actually reported a significant decrease in serum triacylglycerol. Given these limitations, the author's conclusion should be interpreted with caution as it may not be reliable.

Research: The author stated that further research is warranted to investigate the mechanisms that may be related to colonic fermentation and/or incretin release from the distal gut.

Not stated.

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.