Substituting whole grains for refined grains in a 6-wk randomized trial has a modest effect on gut microbiota and immune and inflammatory markers of healthy adults

Background: Observational studies suggest an inverse association between whole-grain (WG) consumption and inflammation. However, evidence from interventional studies is limited, and few studies have included measurements of cell-mediated immunity. Objective: We assessed the effects of diets rich in WGs compared with refined grains (RGs) on immune and inflammatory responses, gut microbiota, and microbial products in healthy adults while maintaining subject body weights. Design: After a 2-wk provided-food run-in period of consuming a Western-style diet, 49 men and 32 postmenopausal women [age range: 40-65 y, body mass index (in kg/m²) <35] were assigned to consume 1 of 2 provided-food weight-maintenance diets for 6 wk. Results: Compared with the RG group, the WG group had increased plasma total alkyresorcinols (a measure of WG intake) (P < 0.0001), stool weight (P < 0.0001), stool frequency (P = 0.02), and shortchain fatty acid (SCFA) producer Lachnospira [false-discovery rate (FDR)-corrected P = 0.25] but decreased pro-inflammatory Enterobacteriaceae (FDR-corrected P = 0.25). Changes in stool acetate (P = 0.02) and total SCFAs (P = 0.05) were higher in the WG group than in the RG group. A positive association was shown between Lachnospira and acetate (FDR-corrected P = 0.002) or butyrate (FDR-corrected P = 0.005). We also showed that there was a higher percentage of terminal effector memory T cells (P = 0.03) and LPS-stimulated ex vivo production of tumor necrosis factor-a (P = 0.04) in the WG group than in the RG group, which were positively associated with plasma alkylresorcinol concentrations. Conclusion: The short-term consumption of WGs in a weightmaintenance diet increases stool weight and frequency and has modest positive effects on gut microbiota, SCFAs, effector memory T cells, and the acute innate immune response and no effect on other markers of cell-mediated immunity or systemic and gut inflammation.