The impact of a high protein diet with strength training on the gastrointestinal microbiota in community dwelling older adults: subanalysis of a randomized controlled trial

Patrick A. Zöhrer^1,2,3Sandra Unterberger^1,3,4Rudolf Aschauer^1,3,4Agnes Draxler^2,3Sophie Somloi²Maria Kapeller²Teresa Bauer²Cornelia Heinz²Stefanie Reichstam²Bernhard Franzke⁵Eva-Maria Strasser⁶Bela Hausmann^7,8Petra Pjevac^8,9David Berry^8,9Barbara Wessner^1,4Karl-Heinz Wagner^1,2*

• ¹Universitat Wien Forschungsplattform Active Ageing, Vienna, Austria
• ²Department of Nutritional Sciences, Faculty of Life Sciences, University of Vienna, Vienna, Austria
• ³Vienna Doctoral School of Pharmaceutical, Nutritional and Sport Sciences (PhaNuSpo), University of Vienna, Vienna, Austria
• ⁴Centre for Sport Science and University Sports, University of Vienna, Vienna, Austria
• ⁵Research Center Health Sciences, FH Campus Wien University of Applied Sciences, Vienna, Austria
• ⁶Karl Landsteiner Institute for Remobilization and Functional Health/Institute for Physical Medicine and Rehabilitation, Kaiser Franz Joseph Hospital, Social Medical Center South, Vienna, Austria
• ⁷Joint Microbiome Facility, Medical University of Vienna and University of Vienna, Vienna, Austria
• ⁸Department of Laboratory Medicine, Division of Clinical Microbiology, Medical University of Vienna, Vienna, Austria
• ⁹Centre for Microbiology and Environmental Systems Science, Department of Microbiology and Ecosystem Science, Division of Microbial Ecology, University of Vienna, Vienna, Austria

Background: A balanced gastrointestinal (GI) microbiota is essential for healthy aging. Although high-protein diets and strength training are recommended for older adults to maintain muscle mass, their effects on GI microbiota remain unclear. Methods: This randomized controlled trial examined the effect of a habitual diet with recommended protein intake or high protein intake combined with strength training on the GI microbiota of 112 community-dwelling adults aged 65–85 years. The participants were divided into three groups: no intervention control (CON), recommended protein intake plus strength training (RP+T), and high protein intake plus strength training (HP+T). Over 17 weeks, protein intake increased significantly from 0.80 (IQR: 0.30-0.50) g/kg body weight at baseline, reaching 1.07±0.25 g/kg in RP+T and 1.62±0.37 g/kg in HP+T groups. Stool samples collected at baseline, after dietary intervention, and after combined dietary and training intervention were analyzed using 16S rRNA gene amplicon sequencing. Results: Despite increased protein intake, microbiota richness, diversity, and composition showed no significant changes within or between groups. Residual energy and inflammatory markers indicated that higher protein intake was well tolerated. Conclusion: The findings suggest that increasing protein intake via food sources up to 1.6 g/kg body weight for more than 4 months, with or without strength training, does not adversely affect the GI microbiota composition in older adults.