Dietary fiber is an integral part of a healthy diet, but questions remain about the mechanisms that underlie effects and the causal contributions of the gut microbiota. Here, we performed a 6-week exploratory trial in adults with excess weight (BMI: 25-35 kg/m) to compare the effects of a high-dose (females: 25 g/day; males: 35 g/day) supplement of fermentable corn bran arabinoxylan (AX; n = 15) with that of microbiota-non-accessible microcrystalline cellulose (MCC; n = 16). Obesity-related surrogate endpoints and biomarkers of host-microbiome interactions implicated in the pathophysiology of obesity (trimethylamine N-oxide, gut hormones, cytokines, and measures of intestinal barrier integrity) were assessed. We then determined whether clinical outcomes could be predicted by fecal microbiota features or mechanistic biomarkers.
AX enhanced satiety after a meal and decreased homeostatic model assessment of insulin resistance (HOMA-IR), while MCC reduced tumor necrosis factor-α and fecal calprotectin. Machine learning models determined that effects on satiety could be predicted by fecal bacterial taxa that utilized AX, as identified by bioorthogonal non-canonical amino acid tagging. Reductions in HOMA-IR and calprotectin were associated with shifts in fecal bile acids, but correlations were negative, suggesting that the benefits of fiber may not be mediated by their effects on bile acid pools. Biomarkers of host-microbiome interactions often linked to bacterial metabolites derived from fiber fermentation (short-chain fatty acids) were not affected by AX supplementation when compared to non-accessible MCC.
This study demonstrates the efficacy of purified dietary fibers when used as supplements and suggests that satietogenic effects of AX may be linked to bacterial taxa that ferment the fiber or utilize breakdown products. Other effects are likely microbiome independent. The findings provide a basis for fiber-type specific therapeutic applications and their personalization.
Clinicaltrials.gov, NCT02322112 , registered on July 3, 2015. Video Abstract.

The initial contact between humans and their colonizing gut microbiota after birth is thought to have expansive and long-lasting consequences for physiology and health. Premature infants are at high risk of suffering from lifelong impairments, due in part to aberrant development of gut microbiota that can contribute to early-life infections and inflammation. Despite their importance to health, the ecological assembly and succession processes governing gut microbiome composition in premature infants remained incompletely understood. Here, we quantified these ecological processes in a spatiotemporally resolved 16S rRNA gene amplicon sequencing data set of 60 extremely premature neonates using an established mathematical framework. We found that gut colonization during the first months of life is predominantly stochastic, whereby interindividual diversification of microbiota is driven by ecological drift. Dispersal limitations are initially small but have increasing influence at later stages of succession. Furthermore, we find similar trends in a cohort of 32 healthy term-born infants. These results suggest that the uniqueness of individual gut microbiota of extremely premature infants is largely due to stochastic assembly. Our knowledge concerning the initial gut microbiome assembly in human neonates is limited, and scientific progression in this interdisciplinary field is hindered due to the individuality in composition of gut microbiota. Our study addresses the ecological processes that result in the observed individuality of microbes in the gastrointestinal tract between extremely premature and term-born infants. We find that initial assembly is mainly driven by neutral ecological processes. Interestingly, while this progression is predominantly random, limitations to the dispersal of microbiota between infants become increasingly important with age and are concomitant features of gut microbiome stability. This indicates that while we cannot predict gut microbiota assembly due to its random nature, we can expect the establishment of certain ecological features that are highly relevant for neonatal health.

Emerging evidence suggests a major role for salivary flow and the viscoelastic properties for taste perception and mouthfeel. Sweet-tasting compounds have also been proposed to have an effect on salivary characteristic. However, it is yet not clarified if perceived differences in the sensorial properties of structural diverse sweet tasting compounds contribute to salivary flow and viscoelasticity of saliva as part of mouthfeel and overall taste perception. Here we hypothesized that sensorially diverse sweeteners would affect salivary characteristics differently. Thus, we investigated the salivary flow, viscoelasticity of saliva, and selected influencing factors including the basal oral microbiome from 21 healthy test subjects after orosensory stimulation with sucrose, rebaudioside M (RebM), sucralose, and neohesperidin dihydrochalcone (NHDC) in a cross-over design. All test compounds enhanced the salivary flow by up to 1.51 ± 0.12 g/min for RebM, compared to 1.10 ± 0.09 g/min for water in the first minute after stimulation. The increase in the flow rate was correlated moderately to the individual perceived sweetness (r= 0.3, p< 0.01), but did not differ between the test compounds. The complex viscosity of the saliva was not affected by the test compounds, but analysis of covariance showed that the complex viscosity was associated (p< 0.05) with the concentration of mucin 5B (Muc5B). The oral microbiome showed a typical composition and diversity but was strongly individual-dependent (PERMANOVA: R²=0.76, p< 0.001), and was not associated with the changes in salivary characteristics. In conclusion, the present study indicates an impact of the individual sweetness impression on the flow rate without measurable changes in the complex viscosity of saliva, which may contribute to overall taste perception and mouthfeel of sweet tasting compounds.