High levels of von Willebrand factor (vWF) have been reported in diabetics with vascular complications, suggesting a role for this protein in the development of cardiovascular complications in non-insulin-dependent diabetes mellitus (NIDDM). Recently, a diet rich in monounsaturated fatty acids (MUFA) has been found to improve glycemic control and decrease diurnal blood pressure as compared with a high-carbohydrate (H-CHO) diet in NIDDM subjects. To study the impact of MUFA on the hemostatic system, we compared the levels of vWF, fibrinogen, fibronectin, and alpha 2-macroglobulin before and after 3 weeks on a high-MUFA (H-MUFA) diet and on an isocaloric H-CHO diet in 15 NIDDM subjects. In a crossover study, the patients were randomly assigned to a H-CHO diet (50% carbohydrate, 30% fat [10% MUFA]) or a H-MUFA diet (30% carbohydrate, 50% fat [30% MUFA]). Before and on the last day of the two diets, vWF, fibrinogen, fibronectin, and alpha 2-macroglobulin levels were measured. The H-MUFA diet caused a decrease in vWF from 1.31 +/- 0.08 to 1.13 +/- 0.08 U/mL (P < .004), whereas an unchanged level was observed after a H-CHO diet (1.19 +/- 0.11 v 1.25 +/- 0.11 U/mL, NS). The relative changes in vWF during 3 weeks on a H-MUFA and on a H-CHO diet attained -12.5% +/- 3.2% versus 5.7% +/- 3.5%, respectively (P < .0001). Furthermore, unchanged levels of fibrinogen, fibronectin, and alpha 2-macroglobulin were seen after usage of the two diets.(ABSTRACT TRUNCATED AT 250 WORDS)