The Dietary Inflammatory Index (DII) was designed to measure the inflammatory potential of one's diet. Evidence from observational studies supports that a higher (ie, more pro-inflammatory) DII score is associated with inflammation and cardiometabolic diseases. We hypothesized that reduction in DII score would improve inflammatory cytokines. To test this hypothesis, we assessed data from a dietary intervention trial in patients with diagnosed coronary heart disease (CHD) to determine whether reduction in DII scores through healthy diets is linked to improvement in inflammatory and related cardiometabolic risk markers. Participants (n = 65, 83% male) were randomized to a Mediterranean diet or low-fat diet intervention for 6-months. Anthropometry, body composition and blood markers were measured and DII scores were calculated from 7-day food diaries. After 6-months, in participants who completed the intervention (n = 56), reduction in DII score correlated significantly with reduction in high sensitivity interleukin-6 (hs-IL-6) (r = 0.34, 95% CI 0.05, 0.56) and triglycerides (r = −0.30, 95% CI -0.51, −0.06) but not with C-reactive protein, adiponectin, glucose, body composition or anthropometry. The adjusted mean difference in hs-IL-6 and triglycerides between the highest and lowest tertiles of DII improvement was −0.47 pg/mL (95% CI 0.41, 1.10) and +0.30 mmol/L (95% CI 1.06, 1.59), respectively. The present study found that improvement in DII score through healthy diet intervention was linked with reduced levels of hs-IL-6, but also increased triglycerides, in adult Australian patients with CHD. Future research is warranted to investigate the impact of change in DII on cardiometabolic risk markers in larger cohorts, other disease populations or healthy subjects and with longer-term follow up.