To measure the consistency and size of the effect of psyllium cereals on the levels of blood total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) in adults.

MEDLINE was searched from 1966 to February 1996, and Current Contents from 1993 to 1996. Studies reported in any lanaguage were sought. Companies known to be conducting research in psyllium cereals were contacted for unpublished studies.

Study designs of evaluations included in the review

Published or unpublished randomised controlled trials (RCTs) with a parallel-group or crossover design.

Specific interventions included in the review

Psyllium cereals and controls. The controls were cereals providing 3 g soluble fibre/day: wheat bran flake cereal, cornflakes, extruded wheat bran cereal, wheat, and bran flake.

Participants included in the review

Adults aged between 27 and 72 years, with mild to moderate hypercholesterolaemia (TC of 5.17 to 7.18 mmol/L), and who consumed a low-fat diet or National Cholesterol Educaion Programme Step 1 or Step 2 diet.

Outcomes assessed in the review

The difference between the baseline and end-of-study lipid levels was assessed. The treatment and control conditions were also compared with regards to the participants' changes in LDL-C category.

How were decisions on the relevance of primary studies made?

One author reviewed the manuscripts for eligibility. The author was aware of the study designs or methodologies being reviewed.

The authors do not state that they assessed validity.

The authors do not state how the data were extracted for the review, or how many of the authors performed the data extraction.

How were the studies combined?

The data were analysed using a linear model to estimate differences between the baseline and end-of-study concentrations of TC, HDL-C and LDL-C, controlling for gender and age. Least-squares means provided the estimates for the size of the effect of psyllium cereal on blood lipid concentrations.

The effect size was reported as an average difference between end-of-study and baseline blood cholesterol concentrations (mmol/L), along with 95% confidence intervals (CIs).

How were differences between studies investigated?

Heterogeneity was investigated by conducting separate analyses of women only divided into two age ranges (less than 50 years, and 50 years and over), and of different age ranges for all participants (less than 39, 40 to 49, 50 to 59, and 60 years and over).

A separate meta-analysis was conducted using only the crossover studies.

Eleven RCTs (one involving two centres was subsequently split into 2 groups which increased the number of studies to 12), of either a crossover design or a design with parallel arms for treatment and control conditions, were included; 5 studies used a parallel-group design and 7 studies used a crossover design. There was a total of 195 participants in the control group and 209 participants in the psyllium group. Seven published studies and 4 unpublished studies were eligible for the meta-analysis.

Only results from the primary meta-analysis were reported in the article. In the second meta-analysis, which used only the first period of the crossover studies, HDL-C decreased by only 0.02 mmol/L (P=0.06); this difference was not significant.

Consistency of effect of treatment: there was no significant interaction between the variables 'treatment' and 'study' for TC, LDL-C, or HDL-C.

Participants who ate a psyllium cereal had lower TC and LDL-C concentrations than those who ate the control cereal: the average difference in TC was -0.31 (95% CI: -0.37, -0.25), and the average difference in LDL-C was -0.35 (95% CI: -0.40, -0.29).

The HDL-C levels were unchanged in participants eating psyllium cereal: the average difference in HDL-C was 0.00 (95% CI: -0.04, +0.03).

There were no significant differences in baseline blood lipid concentrations between the control and psyllium groups.

The cost information reported by the authors in their discussion was drawn from the study by Kinosian and Gisenberg (see Other Publications of Related Interest). A cost analysis was conducted with three alternatives (cholestyramine resin, colestipol and oat bran) for treating people with high blood TC (greater than 6.85 mmol/L). The cost per person per year was estimated to be $1,442 for cholestyramine resin, $879 for colestipol, and $248 for oat bran. In addition, the cost of a dietician to treat hypercholesterolaemia was $163 per year, compared with $1,450 for drug therapy.

The results indicated that consuming a psyllium-enriched cereal as part of a low-fat diet improves the blood lipid profile of hypercholesterolaemic adults above that which can be achieved with a low-fat diet alone.

The authors made a reasonably thorough search of the available literature. They addressed issues of publication bias and language bias by searching for unpublished studies and for those which were published in non-English language publications.

The authors' inclusion criteria and study outcomes were rigorously reported and discussed. The authors performed sensitivity analyses for heterogeneity, the results of which were presented in tabular format and in the text of the review.

The adverse effects mentioned were gastrointestinal discomfort and nausea; however, measurement of them was not reported.

The authors' conclusions appear to follow from the results reported in the review for TC and LDL-C.

Practice: The authors stated that their findings support the incorporation of psyllium cereal into low-fat diets to lower TC and LDL-C in mild to moderate cases of hypercholesterolaemia, and that this is consistent with current dietary guidelines.

Research: The authors did not state any implications for further research.

Kinosian BP, Eisenberg JM. Cutting into cholesterol: cost-effective alternatives for treating hypercholesterolemia. JAMA 1988;259:2249-54.

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.