BACKGROUND AND OBJECTIVES: The complex interplay between diet, gut microbiota, and metabolic health has gained increasing recognition as a key factor in the development of obesity and related conditions, such as sarcopenia. This study examines the relationship between the dietary index for gut microbiota (DI-GM) and sarcopenia, while exploring the potential mediating role of the body roundness index (BRI) in this association. By integrating these factors, our findings aim to shed light on the diet-gut microbiota-sarcopenia interaction and its implications for personalized dietary interventions. RESEARCH DESIGN AND METHODS: Data were obtained from the National Health and Nutrition Examination Survey (NHANES) 2011-2018. Multivariable weighted regression analyses were conducted to assess the association between DI-GM and sarcopenia. Restricted cubic spline analyses were used to evaluate potential non-linear relationships. Additionally, mediation analysis was performed to determine whether the BRI mediated the relationship between DI-GM and sarcopenia. RESULTS: A total of 10,190 participants were included in the study, of whom 7.57% were diagnosed with sarcopenia. In the weighted linear regression analysis, each one-point increase in DI-GM was associated with a 12% reduction in the prevalence of sarcopenia (OR = 0.88, 95% CI: 0.82, 0.95). Specifically, a higher beneficial gut microbiota score was significantly associated with a lower prevalence of sarcopenia (OR = 0.82, 95% CI: 0.75, 0.89). Mediation analysis revealed that BRI accounted for 23% of the total effect of DI-GM on sarcopenia. Among the beneficial components, those with a significant mediation effect contributed approximately 9% of the total effect. DISCUSSION AND IMPLICATIONS: The DI-GM was found to be negatively associated with the prevalence of sarcopenia, with BRI playing a crucial mediating role. These findings highlight the importance of the diet-gut microbiota-sarcopenia interaction and underscore the potential for incorporating dietary and microbiota-targeted interventions in personalized therapeutic strategies for sarcopenia.