Fecal Microbiota and Associated Metabolites are Minimally Affected by Ten Weeks of Resistance Training in Younger and Older Adults

Abstract

Recent evidence suggests that short chained fatty acids (SCFAs) produced by gut microbiota may impact body composition and muscle accretion. Additionally, aging is implicated in negative alterations to the gut microbiome and exercise training has been posited to positively affect gut microbiota. However, limited human evidence indicates that shorter-term resistance training does not appreciably alter the gut microbiome in older adults, and no human study has examined if resistance training differentially alters the gut microbiome and associated SCFAs between younger and older individuals. Therefore, we examined whether 10 weeks of resistance training (RT) differentially altered fecal microbiota composition, fecal and circulating SCFAs, and serum markers associated with gastrointestinal integrity in younger and older adults. Fecal and serum samples were collected from untrained younger (22 ± 2 years, n=12) and older (58 ± 8 years, n=12) participants prior to and following 10-weeks of supervised twice-weekly full body RT. Outcome measures prior to (Pre) and following the training intervention (Post) included body composition measured by dual x-ray absorptiometry, vastus lateralis (VL) thickness measured by ultrasound, fecal microbiome data from 16S rRNA gene sequencing, serum and fecal SCFAs measured by gas chromatography, and serum intestinal fatty acid-binding protein 2 (FABP2), lipopolysaccharide-binding protein (LBP), and leucine-rich alpha-2 glycoprotein (LRG-1) quantified by enzyme-linked immunosorbent assays. Repeated measures two-way (group×time; G×T) ANOVAs were performed for all dependent variables over time, and Spearman correlations were used to explore if changes in training variables were associated with microbiome variables and SCFAs. RT significantly increased VL thickness and lean body mass (p<0.05) in both groups, but no GxT interactions were evident. Although differences in beta diversity were evident between younger and older participants, no significant age, time, or interaction effects were evident. Seven SCFAs were detected in the fecal samples, albeit no significant age, time, or interaction effects were evident. Acetic acid was the only SCFA detected in serum, and no significant age, time, or interaction effects were evident. Serum LRG1 exhibited a significant main effect of time (Pre>Post, p=0.007) and age (Younger>Older, p=0.015), but this marker nor serum FABP2 or LBP exhibited significant interactions. In all younger, older, and/or all participants combined, there were no significant correlations between RT-induced changes in muscle mass-related outcomes and changes in either metrics of fecal microbiome diversity, total or individual SCFAs, or serum FABP2/LBP/LRG-1 (p>0.00067). Our data highlights that 10 weeks of RT largely does not alter the fecal microbiome, associated SCFAs, or select markers of gastrointestinal integrity in untrained younger or older adults.