Although very brief questionnaires are commonly used to assess physical activity, an analogous approach for assessing diet quality within clinical practice has not been developed. Thus, we undertook an exploratory study to evaluate the association between a single-item questionnaire regarding dietary quality and patient risk profiles, lifestyle habits, lipid values, coronary artery calcium (CAC) scores and mortality. We assessed 15,368 patients who underwent CAC scanning, followed for a median of 12.1 years for all-cause mortality. Diet quality was assessed according to a single-item question regarding self-reported adherence to a low saturated fat diet (0 = never, 10 = always), with patients categorized into 4 dietary groups based on their response, ranging from low to very high saturated fat intake. We observed a significant stepwise association between reported saturated fat intake and smoking, exercise activity, obesity, and serum cholesterol, low density lipoprotein, and triglyceride values. Following adjustment for age and risk factors, patients reporting very high saturated fat intake had an elevated hazard ratio for mortality versus low saturated fat intake: 1.22 (95% confidence interval 1.04 to 1.44). The hazard ratio was no longer significant after further adjustment for exercise activity. Upon division of patients according to baseline CAC, a stepwise relationship was noted between increasing saturated fat intake and mortality among patients with CAC scores ≥400 (p = 0.002). Thus, within our cohort, just a single-item exploratory questionnaire regarding very high saturated fat intake revealed stepwise associations with health behaviors and cardiac risk factors, suggesting the basis for further development of a practical dietary questionnaire for clinical purposes.