Association between dietary fiber and markers of systemic inflammation in the Women's Health Initiative Observational Study

Abstract

Objective

Systemic inflammation may play an important role in the development of atherosclerosis, type 2 diabetes, and some cancers. Few studies have comprehensively assessed the direct relations between dietary fiber and inflammatory cytokines, especially in minority populations. Using baseline data from 1958 postmenopausal women enrolled in the Women's Health Initiative Observational Study, we examined cross-sectional associations between dietary fiber intake and markers of systemic inflammation (including serum high-sensitivity C-reactive protein [hs-CRP], interleukin-6 [IL-6], and tumor necrosis factor-α receptor-2 [TNF-α-R2]) in addition to differences in these associations by ethnicity.

Methods

Multiple linear regression models were used to assess the relation between fiber intake and makers of systemic inflammation.

Results

After adjustment for covariates, intakes of dietary fiber were inversely associated with IL-6 (P values for trend were 0.01 for total fiber, 0.004 for soluble fiber, and 0.001 for insoluble fiber) and TNF-α-R2 (P values for trend were 0.002 for total, 0.02 for soluble, and <0.001 for insoluble fibers). Although the samples were small in minority Americans, results were generally consistent with those found among European Americans. We did not observe any significant association between intake of dietary fiber and hs-CRP.

Conclusion

These findings lend support to the hypothesis that a high-fiber diet is associated with lower plasma levels of IL-6 and TNF-α-R2. Contrary to previous reports, however, there was no association between fiber and hs-CRP among postmenopausal women. Future studies on the influence of diet on inflammation should include IL-6 and TNF-α-R2 and enroll participants from ethnic minorities.

Introduction

High-sensitivity serum C-reactive protein (hs-CRP), plasma interleukin-6 (IL-6), and tumor necrosis factor-α receptor-2 (TNF-α-R2) are markers of systemic inflammation in the body and have been associated with many chronic diseases, including coronary heart disease [1], [2], [3], [4], [5], [6], metabolic syndrome [7], [8], [9], diabetes mellitus [10], [11], [12], [13], and cancer [14], [15].

Dietary fiber intake may reduce the risk of these diseases by mediating the proinflammatory process [16], [17], [18]. Two mechanistic hypotheses have emerged. First, dietary fiber may decrease oxidation of glucose and lipids while maintaining a healthy intestinal environment. Second, dietary fiber may prevent inflammation by altering adipocytokines in adipose tissue and increasing enterohepatic circulation of lipids and lipophilic compounds [19]. The link between dietary fiber intake and reduced hs-CRP has been observed in several recent studies, including two analyses using cross-sectional data from the National Health and Nutrition Examination Survey 1999–2000 [20], [21], an analysis using a longitudinal cohort of 524 healthy adults [22], and a small clinical trial [23]. However, one study has examined the association of dietary fiber with the proinflammatory cytokines IL-6 and TNF-α [24] and there is increasing clinical and experimental evidence for an important independent role of TNF-α-R2 signaling in chronic inflammatory conditions [25]. Detailed information regarding dietary fiber–inflammation relations remains sparse, especially among diverse populations and by gender. For example, hs-CRP levels are higher in women than in men [26], [27], and African Americans have higher hs-CRP levels than European Americans [26]; whether there are differences by fiber intake is unclear.

We evaluated the relation between dietary fiber intake and plasma levels of hs-CRP, IL-6 and TNF-α-R2 in 1958 women for whom we had available baseline data on markers of systemic inflammation and dietary intake. These women were in the observational arm of the Women's Health Initiative (WHI) study, a racially and ethnically diverse sample of postmenopausal women in the United States [28].