Soy protein diet significantly improves endothelial function and lipid parameters

Background: Replacement of animal protein with soy protein in the diet is associated with decreased cholesterol levels. However, the effects of soy protein diet on endothelial function are not well known. Hypothesis: The aim of the study was to investigate the effects of soy protein diet on plasma lipids and endothelial function parameters assessed by two different methods. Methods: Twenty hypercholesterolemic, nonsmoker male patients (age 50.1 +/- 11.8 years), with a normal body mass index, were included. After calculating their daily requirements, a diet with 25-30% of energy from fats, 10-12% from proteins, and the rest from carbohydrates was instituted. Sixty percent of the animal source proteins of the diet were substituted by soy. The anthropometric measures, lipid parameters, and endothelial functions of the subjects were assessed at baseline and 6 weeks after soy protein diet. Flow-mediated endothelium-dependent dilatation (EDD) and plasma thrombomodulin (TM) levels were evaluated as endothelial function parameters. Results: After diet, plasma total cholesterol, low-density lipoprotein cholesterol, apolipoprotein B, and triglyceride levels decreased significantly (p < 0.001, p < 0.001, p = 0.039, and p = 0.001, respectively). The mean plasma TM levels were also significantly reduced with diet (p = 0.004). Studies of the brachial artery indicated a borderline dilatation in baseline brachial artery diameter (p = 0.05), however the diameter at reactive hyperemia was significantly larger after diet (p < 0.001), resulting in a significant improvement of EDD (p = 0.002). Conclusion: Soy protein diet significantly improves plasma lipid profile in patients with hypercholesterolemia. Furthermore, the endothelial function, as judged by two different methods (EDD and plasma TM levels), also improves with soy protein diet.