Gastrointestinal Microbial Changes Following Whole Grain Barley and Oat Consumption in Healthy Men and Women

Abstract

BackgroundWhole grain fiber consumption is a promising approach to positively alter the human gastrointestinal (GI) microbiome. The Dietary Guidelines for Americans recommends half of all grain servings be consumed as whole grains to minimize chronic disease risk. However, little is known about the effects of whole grain barley and oat consumption in their whole food forms on GI microbial profiles in healthy individuals.ObjectiveWe aimed to assess the impact of whole grain barley and oat consumption on the GI microbiota in healthy men and women and determine whether effects of whole grain consumption on the GI microbiota are associated with metabolic and immunological improvements.MethodsA 6‐week randomized, double‐blinded, parallel‐arm, controlled‐feeding intervention was undertaken in healthy adults (n=68) fed at weight maintenance. Male and female participants were randomly assigned to 1 of 3 treatments: 1) a control diet containing 0.8 daily servings of whole grain/1800 kcal, 2) a diet containing 4.4 daily servings of whole grain barley/1800 kcal or 3) a diet containing 4.4 daily servings of whole grain oats/1800 kcal. Blood, urine, and fecal samples were collected at baseline and at the end of the intervention period for metabolic, immunologic, and microbial analyses. Bacterial, fungal, and archaeal sequences were generated using an Illumina MiSeq and analyzed with QIIME 1.8. Data were analyzed using SAS 9.4.ResultsPrior to treatments, associations between bacterial taxa and host metabolism were observed. The Bacteriodes:Firmicutes ratio was negatively correlated with BMI (r=−0.31, p=0.009). The abundance of Bifidobacterium was negatively correlated with age (r=−0.40, p=0.0008). Alternatively, Collinsella was positively correlated with age (r=0.26, p=0.03), LDL cholesterol (r=0.21, p=0.09), and triglycerides (r=0.23, p=0.06). Microbial community structure was affected by whole grain barley and oat consumption. Total species richness was higher in participants consuming oats compared with control (p=0.01). Principal coordinates analysis (PCoA) of UniFrac distances between samples based on their 97% OTU composition and abundances indicated that the microbiota of participants within a treatment were more similar than between treatments (p=0.03).ConclusionsOur findings are congruent with previous research demonstrating associations between the GI microbiota, weight status, age, and serum lipids. Ecological analyses revealed that whole grain barley and oats induced changes in the microbial community structure of the Gl microbiota. Additional study is ongoing to delineate the microbial taxa driving these shifts and the interrelationships among changes in the GI microbiota and metabolic improvements.Support or Funding InformationThis study was funded by USDA and the Kellogg Company.