Abstract Sarcopenia, a syndrome characterized by declining muscle mass and function, is associated with various adverse health outcomes. While body mass index (BMI) is a fundamental health indicator, its relationship with sarcopenia is complex and remains inadequately explored. Low BMI has been linked to muscle loss, but the role of other demographic and clinical factors in this relationship is unclear. This cross-sectional study analyzed data from the NHANES 2011–2018 cohort, including 7,455 adults aged ≥ 20 years. Low muscle mass was diagnosed based on appendicular skeletal muscle mass using DXA criteria. BMI was categorized into quartiles for analysis. Weighted multivariable logistic regression assessed associations between BMI and low muscle mass, adjusting for confounders such as age, gender, ethnicity, income-to-poverty ratio, and chronic diseases (e.g., diabetes and hypertension). Variance inflation factors (VIF) confirmed the absence of multicollinearity. Lower BMI was significantly associated with higher odds of low muscle mass (adjusted OR: 0.508, 95% CI: 0.483–0.533, p