Effects of Whole-Grain Consumption on Selected Biomarkers of Systematic Inflammation: A Systematic Review and Meta-analysis of Randomized Controlled Trials

Abstract

Whole grains have potential benefits in preventing cardiovascular diseases and diabetes; nevertheless, results from randomized clinical trials (RCTs) on inflammatory markers are controversial. The aim of this meta-analysis of RCTs was to examine the effect of whole grains on inflammatory markers A systematic literature search was conducted by using the online database of PubMed, Embase, Google Scholar, and Scopus for relevant studies up to November 2017, using Medical Subject Headings and other related keywords. Only studies that compared the effects of whole grains on inflammatory markers with refined grains were included. From more than 2278 articles, 17 RCTs met the inclusion criteria and were systematically reviewed. Weighted mean differences were estimated and pooled effect size was calculated by random effects model. Thirteen RCTs with 466 participants were included in the meta-analysis. Whole-grain consumption had a significant effect on serum concentration of high-sensitivity C-reactive protein (hs-CRP; Hedges’ g: −0.22; 95% confidence interval (CI): −0.45, 0.00; p = 0.047), interleukin-6 (IL-6; −0.28 pg/mL; 95% CI: −0.55, −0.02; p = 0.037) but did not result in a significant decline in serum concentration of tumor necrosis factor alpha (TNF-α; −0.12 pg/mL; 95% CI: −0.39, 0.15; p = 0.396). Significant heterogeneity was observed between studies for hs-CRP (I² = 69.0%, p < 0.0001), IL-6 (I² = 96.6%, p < 0.001), and TNF-α (I² =  95.4%, p < 0.001). In sensitivity analysis, the effect of whole grain intake on hs-CRP, IL-6, and TNF-α was not substantially modified by the result of a single study. Meta-regression for duration showed no significant association between the duration of study and changes in serum C-reactive protein levels (β coefficient = 0.006, standard error = 0.036; p = 0.870).

Conclusions: This meta-analysis of RCTs suggested that whole grains might affect health status via improving systematic inflammation.

Key teaching points:

• We conducted a systematic review and meta-analysis of randomized controlled trials.

• Whole grains consumption was associated with lower serum levels of hs-CRP and IL-6.

• Whole grains cannot significantly decrease serum levels of TNF-α.

• We could not found any source for heterogeneity.

• The effect of whole grains on serum inflammatory biomarkers was independent from duration.

Keywords:

• Whole grains
• inflammation
• randomized clinical trial
• meta-analysis

Acknowledgment

PH and FH designed the study, searched databases, selected eligible studies, extracted data, performed statistical analysis, and wrote the manuscript. The study was supported by Food Security Research Center, Isfahan University of Medical Sciences, Isfahan, Iran.

Transparency declaration

The lead author affirms that this manuscript is an honest, accurate, and transparent account of the study being reported. The reporting of this work is compliant with PRISMA guidelines. The lead author affirms that no important aspects of the study have been omitted and that any discrepancies from the study as planned have been explained.

Conflict of interest

The authors declare that there are no conflicts of interest.