Low Intake of Dietary Fiber Is Associated With Gastrointestinal Inflammation in Healthy U.S. Adults

Abstract

Objectives We examined associations between reported fiber intake and markers of gastrointestinal (GI) inflammation in a healthy human population. Methods Participants in the USDA Nutritional Phenotyping Study completed up to three 24-hour recalls using ASA24 and a Block 2014 Food Frequency Questionnaire (FFQ) to assess recent and habitual intake, respectively. Stool samples were stored on ice immediately after collection and homogenized within 24 hours. Markers of inflammation from stool, including calprotectin, neopterin, and myeloperoxidase (MPO) were measured by ELISA along with LPS-binding protein (LBP) from plasma. Associations were tested using regression models. We compared GI marker levels between participants who consumed low and adequate amounts of fiber according to both dietary assessment tools. Analyses were repeated with the subset of participants who had subclinical levels of calprotectin (< 100 μg/g) and myeloperoxidase (<2000 ng/g). Results There were no significant associations between fiber intake and calprotectin or MPO levels (n = 295). Recent and habitual fiber intake were negatively correlated with neopterin levels (n = 289, P = < 0.001 and P = 0.023, respectively). Fiber groups were determined by lowest quartiles of both dietary instruments and minimum recommendations from the Dietary Guidelines for Americans (low: < 15.9 g/day mean ASA24 & FFQ, n = 35; adequate: >28 g/day, n = 68). Participants with low intake had higher neopterin levels (30.7 ± 9.1 nmol/L) than the adequate intake group (16.5 ± 3.3 nmol/L, P = 0.003). Plasma LBP was higher in participants with low fiber intake (12.8 ± 1.2 μg/mol) than those with adequate intake (9.71 ± 0.62 μg/mL, P = 0.01). When fiber was expressed as g/1000 kcal consumed (low: < 8.6 g/1000 kcal, n = 50; adequate: >14 g/1000 kcal, n = 54), LBP levels were higher in the low intake group (12.5 ± 0.96 μg/mL) than adequate (9.9 ± 0.67 μg/mL, P = 0.03). Habitual fiber intake was negatively correlated with calprotectin in the subset of participants with subclinical levels (P = 0.04). Conclusions Dietary fiber intake was negatively correlated with neopterin and subclinical calprotectin levels. Participants with low intake on both instruments had higher neopterin and LBP than those with adequate intake. Fiber consumption may be protective against GI inflammation in healthy adults. Funding Sources USDA ARS 2032-51,530-026-00D.