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Gut microbiota
Figure 4 Athletes display a pro fi le of short-chain fatty acids (SCFAs) that alters from that of the controls. (A) Heat map of bacterial taxa (family, genus and species level) that correlate with faecal short-chain fatty acid levels using Spearman ’ s correlation. Cool colours represent positive correlations; hot colours represent negative correlations (r). All taxa shown had a correlation p value<0.01. Those marked with * represent correlations with a false discovery rate <0.01 after Benjamini-Hochberg multiple testing corrections. (B) Median concentrations of GC-MS-derived faecal SCFA. Quantitative analysis of SCFAs in faecal samples shows signi fi cant increase in measured concentrations of acetate, propionate, butyrate and valerate in athletes. Error bars represent 95% CIs. (C) Quanti fi cation of statistically relevant correlations of metabolic pathways to GC-MS-derived faecal SCFA concentrations ( μ M). BMI, body mass index; GC-MS, gas chromatography – mass spectrometry.
It was also observed that 16 genera correlated with 12 metabo- lites (see online supplementary table S9).
Correlating metabonomic and metagenomic results Correlation analysis between targeted measurements of SCFAs and taxonomic data from 16S rRNA sequencing revealed a number of correlations that remained signi fi cant following cor- rection; Roseburia was positively correlated with acetate (p=0.004) and butyrate (p=0.018) while Family XIII Incertae Sedis was positively correlated with isobutyrate (p<0.001), iso- valeric acid (p<0.001) and valeric acid (p=0.008) ( fi gure 4A and online supplementary table S7). SCFAs were also correlated with pathway relative abundances, with all SCFAs associating with considerably more pathways in the athletes versus the controls ( fi gure 4C). Multiple statistically signi fi cant (7948) (p<0.05) correlations between the metabolic pathways and SCFAs were identi fi ed (see online supplementary table S8). Two distinct blocks of proportionately discriminant correlations were observed with isobutyric and isovaleric acids, which were more abundant in the athletes, while acetic and butyric acids were proportionately more abundant in controls. Correlations of the SCFA concentrations to pathways related to fermentation, biosynthesis or modi fi cation of fatty acids were identi fi ed among the numerous other associations (see online supplementary table S8 for complete list). Additional correla- tions of metabolic pathways against well-identi fi ed metabolites detected from both faecal water ( fi gure 5A, C) and urine ( fi gure 5B, D) presented numerous signi fi cant associations (6186 and 13 412, respectively; data not shown) (p<0.05).
DISCUSSION The results con fi rm enhancement of microbial diversity in ath- letes compared with controls. Supporting previous insights into the bene fi cial in fl uence of physical exercise and associated diet on the compositional structure of the gut microbiota, 25 26 30 this study has extended the paradigm to include links between physical fi tness and the functional potential of the gut micro- biota and its metabolites. It must be conceded that some ath- letes, although fi t, may not necessarily be more healthy. 31 Athletes have an increased abundance of pathways that — given an equivalent amount of expression activity — could be exploited by the host for potential health bene fi t, including bio- synthesis of organic cofactors and antibiotics, as well as carbo- hydrate degradation and secondary metabolite metabolism. 32 Furthermore, athletes have an enriched pro fi le of SCFAs, previ- ously associated with numerous health bene fi ts and a lean phenotype. 33 – 35 While interpretation of SCFA data can be dif fi - cult as levels represent a combination of SCFA production and host-absorption rates, it is notable that, as previously presented, the athletes ’ diet maintained signi fi cantly higher quantities of fi bre intake. 26 This along with an increased number of detected SCFA pathways in the athletes would be conducive to an enhanced rate of SCFA production 36
BartonW, et al . Gut 2017; 0 :1 – 9. doi:10.1136/gutjnl-2016-313627
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