Background <p>Dietary approaches to stop hypertension (DASH) diet as a balanced dietary pattern is designed to help manage hypertension. The scientific evidence hypothesized that following the DASH diet may lead to reductions in cardiometabolic risk. We aimed to design a clinical trial to assess the impact of the DASH diet on cardiometabolic and atherogenic indices in individuals with metabolic syndrome (MetS).</p> Methods <p>Sixty participants diagnosed with MetS were randomly divided into two groups: the intervention group (adhering to DASH diet) or the control group (following a common healthy diet). Key outcomes of the present study including cardiometabolic index (CMI) as our primary outcome, and atherogenic index of plasma (AIP), atherogenic coefficient (AC) and castelli risk index II (CRI-II) as secondary outcomes were evaluated at the baseline and at the end of the study.</p> Results <p>While one participant excluded from the trial, 59 subjects completed the study. Baseline values of CMI (<i>p</i> = 0.33), AIP (<i>p</i> = 0.27), AC (<i>p</i> = 0.44) and CRI-II (<i>p</i> = 0.17) showed no significant difference between the intervention group and the control group. After adjusting for confounding factors, the intervention group demonstrated a significant decrease compared to the control group in CMI (−0.38±0.29 vs. −0.02±0.47; <i>p</i> = 0.001), AIP (−0.04±0.04 vs. 0.01 ± 0.07; <i>p</i> = 0.001), AC (−0.31±0.54 vs. 0.01 ± 0.72; <i>p</i> = 0.04) and CRI-II (−0.30±0.37 vs. −0.03±0.39; <i>p</i> = 0.009).</p> Conclusions <p>Adherence to the DASH diet appears to be effective in reducing CMI and some atherogenic indices. Further well-designed clinical trials with longer intervention durations are needed.</p> Trial registration <p>The trial was registered on 21 October 2022 at Iranian Registry of Clinical Trials (IRCT20180201038585N12, <a href="https://irct.behdasht.gov.ir/trial/66161">https://irct.behdasht.gov.ir/trial/66161</a>).</p>