The role of skeletal muscle in the prognosis of patients with Type 2 Diabetes Mellitus (T2DM) remains unclear. This study aimed to systematically evaluate the impact of different muscle-mass adjustment standards on adverse health outcomes in middle-aged and elderly T2DM patients. Retrospective cohort study. A total of 1,818 T2DM patients aged 50 years or older were included in this study. The cohort comprised 45.7% females, with a median age of 63 years. Variables closely correlated with total lean mass (TLM) and appendicular lean mass (ALM) were selected as adjustment indicators. The primary composite endpoints were all-cause mortality, cardiovascular disease (CVD), and fragility fractures. Cox proportional hazards models were used to estimate the risk associated with each indicator, and phenotypic characteristics of high-risk patients were evaluated. During a median follow-up of 63 months, 436 patients reached the primary endpoint. ALM/BMI and ALM/weight were negatively correlated with adverse outcomes in both sexes, even after adjusting for confounding factors (males: ALM/BMI (hazard ratio [HR] = 0.998, 95% confidence interval [CI] = 0.996-0.999, P = 0.005) and ALM/weight (HR = 0.924, 95% CI = 0.864-0.987, P = 0.020)
females: ALM/BMI (HR = 0.998, 95% CI = 0.996-1.000, P = 0.030) and ALM/weight (HR = 0.917, 95% CI = 0.860-0.978, P = 0.008), respectively). Individuals with lower ALM/BMI and ALM/weight have poorer metabolic status, greater fat accumulation, more complications, and a lower muscle-to-fat ratio. Our findings demonstrate that both ALM/BMI and ALM/weight can predict adverse health outcomes, suggesting their potential as practical, clinically relevant markers for sarcopenia in T2DM.