Effects of feeding 4 levels of soy protein for 3 and 6 wk on blood lipids and apolipoproteins in moderately hypercholesterolemic men

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Abstract
Background: Replacing animal protein with soy protein has been shown to reduce total and LDL-cholesterol concentrations in humans. However, the minimum amount of soy protein required for significant reduction of blood lipids is not known. Objective: We evaluated the amount of soy protein needed to reduce blood lipids in moderately hypercholesterolemic men. Design: Eighty-one men with moderate hypercholesterolemia (total cholesterol concentration between 5.70 and 7.70 mmol/L) were studied. After a 3-wk lead-in on a Step I diet, total cholesterol was measured and subjects were randomly divided into 5 groups. For 6 wk, each group received 50 g protein/d, which included isolated soy protein (ISP) and casein, respectively, in the following amounts: 50:0, 40:10, 30:20, 20:30, and 0:50 (control group) g. Blood was collected at baseline and weeks 3 and 6 of the intervention. Results: At week 6, significant reductions (P < 0.05) from baseline compared with the control group were found for non-HDL and total cholesterol and apolipoprotein (apo) B for all ISP groups (except total cholesterol with 40 g ISP). At week 3, significant reductions (P < 0.05) were found in apo B for the groups that consumed ≥30 g ISP and in non-HDL cholesterol for the groups that consumed ≥40 g ISP. HDL-cholesterol, apo A-I, lipoprotein(a), and triacylglycerol concentrations were not significantly affected by dietary treatment. Conclusion: Our findings show that consuming as little as 20 g soy protein/d instead of animal protein for 6 wk reduces concentrations of non-HDL cholesterol and apo B by ≈2.6% and 2.2%, respectively.

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