The Effect of Psyllium Fibre on LDL-C, Non-HDL-C, and Apolioprotein-B: A Systematic Review and Meta-analysis

Serum cholesterol is a major modifiable risk factor for cardiovascular disease, which despite considerable reduction in prevalence, remains the leading cause of premature mortality worldwide. Although LDL-C continues to be recognized as the primary therapeutic target, accumulating evidence suggests that alternative lipid parameters, non-HDL-C and apoB, may provide predictive value beyond that of LDL-C alone, in most population categories. Numerous lifestyle strategies have been developed to manage elevated cholesterol concentrations, of which viscous fibre is often encouraged for its beneficial effects on LDL-C reduction. Conversely, the effects of viscous fibre on new lipid markers, non-HDL and apoB, have yet to be defined. Therefore, this study seeks to elucidate the therapeutic potential of psyllium fibre on totality of atherogenic cholesterol and lipoprotein particles in a systematic review and meta-analysis of randomized controlled trials.

Background: Studies have identified viscous dietary fibre as potentially attenuating cholesterol, including psyllium husk that reduces LDL-cholesterol (LDL-C) thus, may alleviate cardiovascular disease (CVD) treatment.

Objective: To update evidence on the effect of psyllium on LDL-C, and provide assessment of its impact on new lipid markers: non-HDL cholesterol (non-HDL-C) and apolipoprotein-B (apoB).

Design: Conduct of the systematic review and meta-analysis will follow the Cochrane handbook for systematic reviews of interventions. The reporting will follow the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines.

Data Sources \& Study Selection: MEDLINE, EMBASE, CINAHL and The Cochrane Central Register of Controlled Trials will be searched using appropriate search terms. Independent reviewers will extract information about study design, sample size, subject characteristics, dose, follow-up, and placebo/compare. RCTs that investigate the effect of psyllium fibre on LDL-C, non-HDL-C or apoB will be included with a minimum follow-up period ≥ 3 weeks. The amount of psyllium fibre must be reported and effects on outcomes LDL-C, non-HDL-C or apoB must be isolatable. Studies detailing sufficient information for non-HDL-C calculation will also be considered. Unpublished trials are considered and no restriction placed on language.

Outcomes: LDL-C, non-HDL-C, apoB

Data Extraction: Mean±SEM values will be extracted for all outcomes. Standard computations and imputations will be used to derive missing variance data. Risk of bias and overall study quality will be assessed using the Cochrane Risk of Bias tool and GRADE approach.

Data Synthesis: Data will be pooled using the generic inverse variance method with random effects models. Heterogeneity assessed by the Cochran Q-statistic and quantified by I2. Sensitivity analysis and a priori subgroup analyses will be performed to explore sources of heterogeneity. A spline curve model (MKSPLINE procedure) will be utilized to illustrate a non-linear dose-response curve. Publication bias will be investigated by visual inspection of funnel plots and formally tested using Egger's and Begg's tests. If significant, a Trim and Fill analyses will be performed.

Eligibility Criteria:
Inclusion Criteria:

* human trials
* RCT that investigates the effect of psyllium fibre on LDL-C, non-HDL-C and/or apoB
* suitable control
* minimum follow up period ≥ 3 weeks
* amount of psyllium fibre must be report and effect on outcomes isolatable

Exclusion Criteria:

* follow up \< 3 weeks
* non-human trials
* lack of suitable control
* no viable endpoint data