This study was undertaken to compare the effects on plasma cholesterol concentration of a new isolated soy protein in which the protein structure is kept in its native, nondenaturated form (verum 1) versus a conventional isolated soy protein (verum 2) and milk protein (placebo). This prospective, randomized, double-blind, placebo-controlled study was conducted in an outpatient clinical study center in Berlin, Germany. Over 8 wk, 120 patients (total cholesterol, 5.2-7.8 mmol/L) were given verum 1, verum 2, or placebo at a dosage of 25 g protein daily. At the end of the treatment period, total cholesterol levels were significantly reduced by 10.7% in the verum 1 group compared with placebo (P<.001), and levels were reduced by 5.8% in the verum 2 group (P=.008). The difference between the 2 verum groups was statistically significant (P=.008). Low-density lipoprotein cholesterol levels were significantly reduced with nondenaturated isolated soy protein only: levels were reduced by 9.4% in the verum 1 group (P=.002) and by 4.9% in the verum 2 group (P=.107). Again, the difference between the verum groups was significant (P=.05). The results of this study confirm that supplementation with isolated soy protein can lead to significant reductions in plasma concentrations of total and low-density lipoprotein cholesterol. These reductions are significantly more pronounced with an isolated soy protein that maintains the native protein structure than with a commercially available reference isolated soy protein.