INTRODUCTION: There is an increase in awareness about the role of nutritional factors in chronic non-communicable diseases. We therefore conducted this study with an aim to assess the relationship between nutritional factor (vitamin B12 and homocysteine [Hcy]) and its association with insulin resistance and inflammatory markers, and differences in traditional and non-traditional risk factors among diabetics and non-diabetics in known cases of coronary artery disease (CAD). MATERIALS AND METHODS: Three hundred consecutive patients with known coronary disease on coronary angiography, who were >25 years old were included in this study. All cases were interviewed using a questionnaire. Blood samples were analyzed for insulin, vitamin B12, Hcy and inflammatory markers (highly sensitive C-reactive protein [hsCRP], interleukin-6 [IL-6], Tumor necrosis factor-alfa [TNF-α]). Insulin resistance was calculated with homeostasis model assessment of insulin resistance (HOMA-IR). RESULTS: Mean age of the patients was 60.95 ± 12.3 years. Body mass index and waist hip ratio were comparable in both groups. Triglyceride, very low-density lipoprotein and HbA1C were significantly higher and high-density lipoprotein (HDL) was significantly lower in patients with diabetes. Patients with diabetes had significantly high levels of IL-6, hsCRP and TNF-α compared with non-diabetic patients. Insulin resistance was twofold higher in diabetic patients. Serum vitamin B12 levels were significantly lower and Hcy was significantly higher in the diabetic group compared with the non-diabetic patients. HbA1C, HOMA-IR and Hcy levels were positively correlated with inflammatory markers in the total study population and in the non-diabetic patients; but, in diabetic patients, HbA1C and Hcy showed this relation. CONCLUSIONS: Vitamin B12 deficiency is common in the diabetic population. Hcy levels were higher in diabetics compared with non-diabetics, and were related to glycemic level and insulin resistance in diabetic patients. Patients with diabetes had higher traditional risk factors than patients without diabetes in known patients with CAD. Glycemic status was associated with insulin resistance and inflammatory markers.