Cholesterol-lowering effects of oat β-glucan: a meta-analysis of randomized controlled trials

Abstract

Background: Health claims regarding the cholesterol-lowering effect of soluble fiber from oat products, approved by food standards agencies worldwide, are based on a diet containing ≥3 g/d of oat β-glucan (OBG). Given the number of recently published randomized controlled trials (RCTs), it is important to update the findings of previous meta-analyses.

Objective: The objective was to quantify the effect of ≥3 g OBG/d on serum cholesterol concentrations in humans and investigate potential effect modifiers.

Design: A meta-analysis was performed on 28 RCTs comparing ≥3 g OBG/d with an appropriate control. Systematic searches were undertaken in PubMed, AGRICOLA, and Scopus between 1 January 1966 and 6 June 2013, plus in-house study reports at CreaNutrition AG. Studies were assessed with regard to inclusion/exclusion criteria, and data were extracted from included studies by reviewers working independently in pairs, reconciling differences by consensus. Estimates of the mean reduction in serum cholesterol from baseline between the OBG and control diets were analyzed by using random-effects meta-analysis models and meta-regression.

Results: OBG in doses of ≥3 g/d reduced low-density lipoprotein (LDL) and total cholesterol relative to control by 0.25 mmol/L (95% CI: 0.20, 0.30; P < 0.0001) and 0.30 mmol/L (95% CI: 0.24, 0.35; P < 0.0001), respectively, with some indication of heterogeneity (P = 0.13 and P = 0.067). There was no significant effect of OBG on high-density lipoprotein (HDL) cholesterol or triglycerides and no evidence that dose (range across trials: 3.0-12.4 g/d) or duration of treatment (range: 2-12 wk) influenced the results. LDL cholesterol lowering was significantly greater with higher baseline LDL cholesterol. There was a significantly greater effect for both LDL and total cholesterol in subjects with diabetes compared with those without (although based on few studies).

Conclusions: Adding ≥3 g OBG/d to the diet reduces LDL and total cholesterol by 0.25 mmol/L and 0.30 mmol/L, respectively, without changing HDL cholesterol or triglycerides.

Keywords: HDL cholesterol; LDL cholesterol; meta-analysis; oats; total cholesterol; triglyceride; β-glucan.

FIGURE 1

Flow diagram. EC2: not sufficiently or appropriately controlled: only baseline data provided and no control group during the treatment period or an inappropriate control group (e.g., another soluble fiber). EC4: any uncontrolled significant changes during the trial known to affect blood lipid concentration—for example, a significant difference in total fat or saturated fat intake between control and intervention groups, diets contain other soluble fibers than soluble nonstarch polysaccharide from oats, or uncontrolled significant body weight change (note: important only if interventions are affected differently). EC7: insufficient information to estimate the magnitude of the effect: no measure or estimate of soluble fiber or oat β-glucan intake or limited amount of information on the outcome measures. IC9: a formal assessment of diet and body weight changes during the trial. MW, molecular weight; RCT, randomized controlled trial; TC, total cholesterol.

FIGURE 2

Forest plots of estimates of mean differences (95% CIs). LDL cholesterol: heterogeneity (χ², P = 0.13; I² = 22%) (A). TC: heterogeneity (χ², P = 0.067; I² = 28%) (B). The area of the circle is proportional to the inverse variance of the estimate of mean difference. For studies with more than one OBG arm, the number of subjects randomized equals those randomly allocated to the particular OBG arm plus those to the control arm. For Beck et al. (16), the 2 OBG doses were 5–6 and 8–9 g/d. For Davidson et al. (28), the 3 OBG doses were 84 g oatmeal (3.6 g/d), 56 g oat bran (4 g/d), and 84 g oat bran (6 g/d). For Wolever et al. (12), the 4 OBG doses were 4 g/d low MW (4L), 3 g/d medium MW (3M), 4 g/d medium MW (4M), and 3 g/d high MW (3H). diff, difference; MW, molecular weight; OBG, oat β-glucan; TC, total cholesterol; up, unpublished.

FIGURE 3

Forest plots of estimates of mean difference (95% CIs). HDL cholesterol: heterogeneity (χ², P < 0.001; I² = 81%) (A). Triglycerides: heterogeneity (χ², P = 0.58; I² = 0%) (B). The area of the circle is proportional to the inverse variance of the estimate of mean difference. For studies with more than one OBG arm, the number of subjects randomized equals those randomly allocated to the particular OBG arm plus those to the control arm. For Beck et al. (16), the 2 OBG doses were 5–6 and 8–9 g/d. For Davidson et al. (28), the 3 OBG doses were 84 g oatmeal (3.6 g/d), 56 g oat bran (4 g/d), and 84 g oat bran (6 g/d). For Wolever et al. (12), the 4 OBG doses were 4 g/d low MW (4L), 3 g/d medium MW (3M), 4 g/d medium MW (4M), and 3 g/d high MW (3H). diff, difference; MW, molecular weight; OBG, oat β-glucan; up, unpublished.

FIGURE 4

Funnel plots of inverse SE compared with the estimate of mean difference for LDL cholesterol (A) and TC (B). Shading of circles indicates the number of 6 quality questions (Q9a, random sequence generation; Q9b, treatment allocation concealed randomization; Q11, blinding of subjects; Q12, blinding of caregivers; Q13, blinding of outcome assessors; and Q14, reporting of subject compliance) with “yes”: empty, 0; lines, 1–3; hashed, 4–5; and solid, 6. The area of a circle is proportional to the inverse variance of estimate of mean difference. Q, question; TC, total cholesterol.