Background and objective <p>The composite dietary antioxidant index (CDAI) is a tool to assess an individual’s comprehensive dietary antioxidant intake profiles. This study aimed to explore the association between energy-adjusted composite dietary antioxidant index (E-CDAI) and sarcopenic obesity (SO).</p> Methods <p>Participants from the NHANES cohort (<i>n</i> = 4388) and the Tongde Hospital of Zhejiang Province cohort (<i>n</i> = 276) were enrolled in the present study. Logistic regression analyses were applied to explore the association between E-CDAI (both continuous and quintiles) and SO. Moreover, the mediating effect of inflammatory/nutritional indicators were evaluated to investigate the association between E-CDAI and SO.</p> Results <p>In the NHANES cohort, logistic regression demonstrated a significant inverse correlation between E-CDAI and SO (adjust odd ratio (OR)_continuous =0.89, 95% CI = 0.81, 0.98, <i>P</i> = 0.041; adjust OR_Q5vsQ1 =0.44, 95% CI = 0.29, 1.18, <i>P</i>_trend =0.050) In the Chinese population cohort, an inverse correlation also existed between E-CDAI and SO (adjust OR_continuous =0.72, 95% CI = 0.60, 0.87, <i>P</i> &lt; 0.001; adjust OR_Q5vsQ1 =0.30, 95% CI = 0.13, 0.74, <i>P</i>_trend &lt;0.001). Applying data from the NHANES cohort, the mediation analysis indicated that neutrophil-percentage-to-albumin ratio mediated 12.812% and C-reactive protein mediated 6.485% of the associations between E-CDAI and SO.</p> Conclusion <p>A decreased E-CDAI score is associated with the increased risk of SO in adults. The association appeared to be partially mediated through inflammatory/nutritional pathways, suggesting that the E-CDAI may serve as a valuable indicator for identification of individuals at risk for SO.</p>