High intake of dietary fiber is associated with decreased inflammation and all-cause mortality in patients with chronic kidney disease (CKD), according to researchers.

An analysis of data from 14,533 participants in the third National Health and Nutrition Examination Survey showed that each 10 g/day increment in total fiber intake is associated with 38% and 11% decreased likelihood of having elevated C-reactive protein (CRP)—a marker of systemic inflammation—in patients with and without CKD, respectively, after adjusting for age, gender, race, and numerous comorbid conditions and laboratory measures, according to a report in Kidney International (published online ahead of print).

The investigators, led by Vidya M. Raj Krishnamurthy, MD, of University of Utah School of Medicine in Salt Lake City, defined CKD as an estimated glomerular filtration rate below 60 mL/min/1.73 m2 and an elevated CRP as a serum CRP level above 3 mg/L.

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In addition, each 10 g/day increment in total dietary fiber was associated with a 19% decreased risk of all-cause mortality in the CKD subpopulation. Dietary fiber was no longer associated with mortality in this population after adjusting for serum CRP, suggesting that reduction in inflammation is a possible mechanism by which dietary fiber lowers mortality in CKD patients, according to researchers. The study found no association between dietary fiber intake and all-cause mortality in the non-CKD participants.

The authors noted that various mechanisms could explain the association between high dietary fiber intake and decreased serum CRP. Dietary fiber may inhibit inflammation by lowering glycemic load of rapidly digestible and absorbable dietary carbohydrates, they pointed out. High fiber diets have been associated with higher plasma levels of adiponectin, which has anti-inflammatory properties.

Another possibility is related to toxic substances such as phenols, indoles, and amines produced by colonic bacterial metabolism. These metabolic end products are absorbed from the gut and might have a role in systemic inflammation, they stated. These substances normally would be  excreted via the kidney, but they accumulate in patients with kidney disease. This could explain why the association of higher dietary fiber with lower inflammation is stronger in the CKD than non-CKD population. By altering gut bacterial metabolism, they observed, a high-fiber diet likely decreases production and absorption of these toxins, thus decreasing systemic concentrations of these toxins more in the CKD population than in the non-CKD population.

With regard to study limitations, the authors noted that their study was observational and retrospective, which limits causal inference. In addition, residual confounding due to unmeasured variables cannot be ruled out and diet was assessed using only a single 24-hour diet recall.