Associations of Diabetes Mellitus Status and Geriatric Nutritional Risk Index with the Gut Microbiota in Nursing-Home Residents

Background/Objectives: Malnutrition and diabetes mellitus (DM) have been linked to gut microbial perturbations, yet data are scarce for the aging population, especially in a nursing-home setting. As this group is generally at risk for malnutrition, we aimed to investigate the link between DM and gut microbial patterns in interaction with nutritional risk status in nursing-home residents. Methods: Stool samples were collected from 173 nursing-home residents (77.5% female, mean age 86 years) and were analyzed via 16S rRNA sequencing. Furthermore, the Geriatric Nutritional Risk Index (GNRI) was assessed and data on comorbidity status, anthropometric measurements, and medication were acquired. Results: Fifty-one residents had DM (mean HbA1c 6%). There were no DM-related differences in alpha diversity (observed richness: p = 0.733; Shannon index: p = 0.747). PERMANOVA revealed slight differences in beta diversity according to GNRI (R2 = 0.009, p = 0.032), but no significant differences when adding DM status. Differential abundance analysis showed Clostridium_Clostridiaceae, Haemophilus, Actinomycetaceae and Micrococcaceae as significantly decreased with DM, independent of age, sex, and BMI. No interaction between DM and the GNRI in microbial diversity or composition was found. Conclusions: We report malnutrition-related differences in beta diversity and diabetes-related microbial taxa differences in nursing-home residents. DM status did not influence the relationship between the GNRI and gut microbiota in this population.