Obesity significantly impacts bone health. The ABSI is an innovative metric for assessing obesity, offering greater accuracy than traditional measures such as body mass index and waist circumference in reflecting visceral fat accumulation. This study aims to investigate the relationship between ABSI and BMD as well as its association with osteoporosis among U.S. adults, utilizing data from the NHANES. This cross-sectional study analyzed data from adults aged 18 years and older, collected during the 2005-2006, 2013-2014, and 2017-2018 cycles of the NHANES. Multivariate linear regression models were used to evaluate the association between ABSI and BMD. Multivariate logistic regression models were applied to assess the relationship between ABSI and osteoporosis. Restricted cubic spline models were employed to evaluate potential nonlinear associations between ABSI and BMD as well as osteoporosis. Additionally, subgroup analyses and sensitivity analyses were conducted to ensure the robustness of the findings. A total of 5487 participants were included in the analysis, with a mean age of 47.04 years. ABSI was found to be negatively associated with BMD at the femoral neck, total femur, and lumbar spine. Participants in the highest ABSI quartile exhibited a significantly higher prevalence of osteoporosis compared to those in the lowest quartile (OR = 1.95; 95% CI 1.61-2.26). Nonlinear relationships were observed between ABSI and BMD at the femoral neck, total femur, lumbar spine, and osteoporosis, with inflection points at 8.84, 8.56, 9.23, and 8.14, respectively. Sensitivity analyses confirmed the robustness of these associations. Subgroup analyses revealed significant interactions between ABSI and BMD in smokers (P < 0.05). This study identifies a significant negative association between ABSI and BMD and a positive association with osteoporosis. The nonlinear relationship observed between ABSI and both BMD and osteoporosis underscores the importance of maintaining an optimal ABSI to promote bone health. These findings support the utility of ABSI as a valuable marker for early identification and prevention of osteoporosis, offering actionable insights for clinical and public health strategies. Future longitudinal research is warranted to validate these results and further elucidate the underlying mechanisms.