Gut microbiota mediated benefits of barley kernel products on metabolism, gut hormones, and inflammatory markers as affected by co-ingestion of commercially available probiotics: a randomized controlled study in healthy subjects

Background and aims Barley kernel based products have been shown to induce benefits on blood glucose regulation, cardio-metabolic risk markers and appetite regulating hormones in a time perspective of 11–16 h after intake. The mechanisms have been assigned to gut fermentation of indigestible carbohydrates. The purpose of the present study was to evaluate if the modulatory effects of barley on markers of metabolic- and appetite regulation are affected by a dietary background including a mixture of commercially available probiotics. Methods Barley kernel bread was included in the normal diet of 21 healthy subjects in two 4-day intervention periods; with (BB-pro) or without (BB) dietary supplement with a combination of probiotics (Bifidobacterium animalis DN-173 010, Lactobacillus reuteri DSM 17938, and Lactobacillus plantarum 299v). A white wheat flour based bread was included as a reference product (WWB-ref) in a separate 4-day bread intervention period. A cross-over design was applied concerning BB- and WWB-ref; the BB-pro intervention was last in the test sequence. The BB-pro intervention was preceded by 10 days priming with probiotics. The 4 day BB- and WWB-ref intervention periods included dietary supplementation with placebo, and the interventions were preceded with 10 days priming with the placebo. The day after each intervention period, blood samples were collected at fasting and postprandially after a standardized breakfast (0–210 min) for determination of markers of glucose metabolism (blood glucose, serum (s-) insulin), inflammation (s-IL-6, s-IL-18, s-CRP, PAI-1), and concentrations of gut derived hormones involved in satiety and glucose homeostasis (plasma (p-) PYY, p-GLP-1) and intestinal barrier integrity (p-GLP-2). Breath hydrogen was determined as a marker of colonic fermentation. Results Four days intervention with BB, in comparison to WWB-ref, lowered blood glucose response after a subsequent standardized breakfast (0–210 min, P < 0.05). BB and BB-pro interventions increased p-GLP-1 (0–120 min, P < 0.05) and breath H2 (0–210 min, P < 0.05). BB-pro intervention, in comparison to BB and WWB-ref, increased levels of s-PAI-1 (P < 0.05), and p-GLP-2 (0–210 min, P < 0.05) after the standardized breakfast. Conclusions With the exception of increased p-GLP-2 and an unexpected increase in s-PAI-1 concentrations, co-ingestion of a mixture of probiotics did not affect the metabolic outcome of BB; neither positively nor importantly negatively. The study was registered at: ClinicalTrials.gov, register number NCT01718418 (www.clinicaltrials.gov/ct2/show/NCT01718418).