AIMS/BACKGROUND: The relationship between cardiovascular disease and the inflammatory potential of diet has been recently reported. This study aimed to investigate the relationship between a pro-inflammatory diet, as assessed by the dietary inflammatory index (DII), and the atherogenic index of plasma (AIP) and biochemical markers in patients with atherosclerotic heart disease. METHODS: This study was conducted with 100 patients with atherosclerotic heart disease who were admitted or hospitalised at the Department of Cardiology, Erciyes University Faculty of Medicine between March and September 2024. Participants' sociodemographic variables, anthropometric measurements, and biochemical markers were recorded. Their AIP and DII values were calculated. The 14-item Mediterranean Diet Adherence Tool and the Global Physical Activity Questionnaire were administered to them. RESULTS: In our study, DII scores ranged from (-0.50) to (+12.20). Patients were divided into three groups based on their DII scores; T1 and T3 represented lower and higher DII scores, respectively. There were no significant differences in AIP values among the groups (p > 0.05). There were also no differences among the groups in serum Na, K, Ca, fasting blood glucose (FBG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), and C-reactive protein (CRP) values (p > 0.05 for all); only Hemoglobin (Hb) value was higher in the T1 group compared to the other groups (p = 0.014). Participants in the T1 group had higher intakes of energy, total fat, carbohydrates, protein, monounsaturated fat, polyunsaturated fat, fiber; beta-carotene, thiamine, riboflavin, niacin, folic acid, and vitamins A, E, C, and B6; and iron and zinc (p < 0.001 for all). Significant differences were observed among the groups in the intake of saturated fat (p = 0.020), vitamin B12 (p = 0.030), magnesium (p < 0.001), garlic (p = 0.004), onion (p < 0.001), and pepper (p < 0.001), whereas no significant differences were found for cholesterol, vitamin D, selenium, and tea consumption (p > 0.05). No associations were observed between DII and HDL-C, LDL-C, TG, TC, CRP, AIP, Global Physical Activity Questionnaire (GPAQ) score, or the 14-item Mediterranean Diet Adherence score after adjustment for confounders in the whole cohort (p > 0.05 for all). CONCLUSION: This study demonstrates that patients with atherosclerotic heart disease tend to have more pro-inflammatory dietary habits, which are significantly correlated with energy intake and various macronutrient and micronutrient levels. Although there is no direct association between DII and AIP or key biochemical markers, continued pro-inflammatory dietary habits in patients may increase inflammation, potentially affecting the development and progression of atherosclerosis. Accordingly, reducing the inflammatory load of the diet may be a beneficial strategy for preventing and managing atherosclerosis and related cardiovascular diseases.