Gut Microbiota Associated with Type 2 Diabetes and Dietary Balance in Older Adults: A Longitudinal Community-Based Cohort in China

Purpose: This prospective cohort study with a nested case–control analysis aimed to identify gut microbial taxa associated with type 2 diabetes in older Chinese adults and to examine whether dietary balance influences diabetes-related microbial features. Patients and Methods: This study included 507 community-dwelling adults aged 65 years and older from the Surveillance and Management of Disability and Cognitive Impairment in Older Adults (SUM-DCI) cohort. Fecal samples were collected at baseline and analyzed using 16S ribosomal RNA gene sequencing to characterize gut microbial composition. Diabetes status was defined by fasting plasma glucose concentration ≥ 7.0 mmol/L or a self-reported physician diagnosis. A nested case–control study of 93 individuals (31 cases) was conducted within the baseline non-diabetic population to evaluate prospective associations. Metastats and Multivariate Association with Linear Models (MaAsLin) were used to identify diabetes-associated microbial taxa. Dietary intake was assessed using a self-reporting food frequency questionnaire, dietary balance was quantified using the Chinese Dietary Balance Index-22. Multivariable logistic regression was used to evaluate associations between dietary balance and gut microbial abundance. Results: Roseburia abundance was significantly lower in individuals with type 2 diabetes (FDR -adjusted P < 0.05). Higher baseline Roseburia abundance was associated with a lower risk of incident diabetes (OR: 0.225, 95% CI: 0.115– 0.818, P< 0.05). Low soybean intake was independently associated with reduced Roseburia abundance (OR: 0.61, 95% CI: 0.39– 0.94, P< 0.05), whereas overall dietary imbalance scores were not significantly related. Conclusion: Reduced Roseburia abundance is linked to both prevalent and future incident type 2 diabetes among older adults. Low soybean intake may contribute to this microbial depletion, suggesting a potential mechanism by which dietary habits influence diabetes risk through modulation of the gut microbiota. Keywords: gut microbiota, Roseburia, type 2 diabetes, dietary balance, older adults