Aims Diet is a determinant of cardiovascular diseases (CVD) with coronary disease as predominant cause of pre-mature death. To analyse how diet was associated with coronary atherosclerosis, including plaque features.Methods and results The cross-sectional population-based study using data from the Swedish CArdioPulmonary BioImage Study (SCAPIS) included 24 079 adults aged 50-64 years, recruited in 2013 to 2018 who were free of clinical cardiovascular disease. The recruitment and comprehensive examinations were conducted at six locations in Sweden. A dietary index (DI) based on a previously published anti-inflammatory DI including high proportion of plant-based foods, and low in red or processed meat and sugar-sweetened beverages was constructed. The reference group was within lowest DI tertile. Coronary atherosclerosis assessed by coronary computed tomography angiography, including any-, significant-, and adverse or high-risk coronary plaque, which is non-calcified with a significant stenosis >= 50%. Lowest, compared to highest DI tertile was associated with younger age, more often men (62.2% vs. 32.9%), higher high-sensitive C-reactive protein, more cardiometabolic risk and smokers, higher alcohol-, and higher energy-intake. In the highest and lowest tertile, coronary plaques were present in 36.3% and 44.3%, respectively, stenosis >= 50% in 3.7% and 6.0%. Non-calcified coronary plaques with stenosis >= 50% were present in 0.9% and 1.5% in highest and lowest tertiles. In multivariable analyses, the lowest tertile of DI was associated with high-risk plaque features after adjusting for age, sex, smoking, with waist circumference, triglycerides (TGs), and hypertension as possible mediators.Conclusion A low-fibre diet with high red meat content was associated with high-risk plaques features, increased coronary calcification and significant stenosis. Waist circumference, TGs, and hypertension emerged as potential mediators of these associations, underscoring the role of metabolic and hemodynamic factors in the dietary impact on coronary atherosclerosis. Our findings strengthen the importance of cardioprotective dietary recommendations.