Abstract
Rye kernel bread (RKB) evening meals improve glucose tolerance, enhance appetite regulation and increase satiety in healthy volunteers. These beneficial effects on metabolic responses have been shown to be associated with increased gut fermentation. The present study aimed to elucidate if RKB evening meals may cause rapid alterations in microbiota composition that might be linked to metabolic-, immune-, and appetite- parameters. Gut-brain axis interaction was also studied by relating microbiota composition to amount of brain-derived neurotrophic factor (BDNF) in blood plasma. Nineteen healthy volunteers, ten women and nine men aged 22–29 years, BMI < 25 (NCT02093481) participated in the study performed in a crossover design. Each person was assigned to either white wheat bread (WWB) or RKB intake as a single evening meal or three consecutive evenings. Stool and blood samples as well as subjective appetite ratings were obtained the subsequent morning after each test occasion, resulting in four independent collections per participant (n = 76). DNA was extracted from the fecal samples and V4 hypervariable region of the bacterial 16S rRNA genes was sequenced using next generation sequencing technology. Higher abundance of Prevotella and Faecalibacterium with simultaneous reduction of Bacteroides spp. were observed after RKB meals compared to WWB. The associations between metabolic test variables and microbiota composition showed a positive correlation between Bacteroides and adiponectin levels, whereas only Prevotella genus was found to have positive association with plasma levels of BDNF. These novel findings in gut-brain interactions might be of importance, since decreased levels of BDNF, that plays an essential role in brain function, contribute to the pathogenesis of several major neurodisorders, including Alzheimer's. Thus, daily consumption of Faecalibacterium- and/or Prevotella-favoring meals should be investigated further for their potential to prevent neurodegenerative processes in the brain.
Highlights
Colonization of the intestinal tract with commensal microorganisms occurs immediately after birth, establishes during digestive and immune system maturation in early childhood and remains relatively stable in healthy adults [1, 2]
The operational taxonomic units (OTUs) assigned taxonomically to family level resulted in 37 families, the 20 most abundant being shown in Figure 1C, only three were dominating, represented by Bacteroidaceae (32%), Ruminococcaceae (17%), and Lachnospiraceae (14%)
It is worth mentioning that the Prevotellaceae family showed the highest variation within the cohort, ranging from 0.003 to 59%
Summary
Colonization of the intestinal tract with commensal microorganisms occurs immediately after birth, establishes during digestive and immune system maturation in early childhood and remains relatively stable in healthy adults [1, 2]. Despite the relatively stable microbiome in a healthy population, alterations in colonic microbiota composition may occur relatively rapidly after intake of indigestible carbohydrates, i.e., dietary fibers. It is well-known, that dietary fibers in the colon can be used as substrates for fermentation process, depending on the individual fermentative capacity of different bacterial species [4,5,6]. The positive effects of barley kernel-based meals were strongly associated with colonic fermentation and linked to alterations in the bacterial family Bacteroidaceae, an increase in Prevotella and decrease in Bacteroides abundance [17]. Functional changes of microbiota after rye kernel-based meals, such as increased concentrations of breath hydrogen and production of SCFAs and, especially, of butyrate and propionate, have previously been reported [15]
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