Gut Microbiota Enterotype as a Predictor of Sarcopenia in the Japanese Elderly Population

<b>Background/Objectives</b>: Frailty and sarcopenia are age-related conditions that impair quality of life in older adults. Although the gut microbiota affects muscle health, its role in sarcopenia remains unclear. This study investigated the association between gut microbiota enterotypes and sarcopenia in community-dwelling older Japanese adults. <b>Methods</b>: In this cross-sectional study, 322 community-dwelling adults from the Japanese Frailty Scale cohort aged ≥65 years were assessed for sarcopenia using standardized criteria. Physical measures included grip strength, gait speed, and skeletal muscle mass index (SMI). Gut microbiota profiles were analyzed using 16S rRNA sequencing and classified into four enterotypes (ET-B1, ET-B2, ET-R, ET-P). Associations with sarcopenia were evaluated using multivariable logistic regression. <b>Results</b>: Participants with enterotype ET-B2 had significantly lower microbial diversity (<i>p</i> < 0.01) and reduced grip strength (<i>p</i> < 0.05), whereas the difference in SMI compared with ET-P individuals did not reach statistical significance (<i>p</i> = 0.0625). Sarcopenia prevalence differed significantly between enterotypes (<i>p</i> < 0.01). A predictive model incorporating age and ET-B2 exhibited an area under the receiver operating characteristic curve (AUC) of 0.795, significantly higher than the age-only model (AUC = 0.686, DeLong's test, <i>p</i> < 0.05). <b>Conclusions</b>: Gut microbiota composition, especially enterotype ET-B2, is significantly associated with sarcopenia in older Japanese adults. These findings indicate the potential for using the gut microbiota as a biomarker and therapeutic target in treating age-related muscle decline.