Effect of Two Types of Soy Milk and Dairy Milk on Plasma Lipids in Hypercholesterolemic Adults: A Randomized Trial

Objective: To compare the effects of two commercially available soy milks (one made using whole soy beans, the other using soy protein isolate) with low-fat dairy milk on plasma lipid, insulin, and glucose responses. Design: Randomized clinical trial, cross-over design. Subjects: Participants were 30–65 years of age, n = 28, with pre-study LDL-cholesterol (LDL-C) concentrations of 160–220 mg/dL, not on lipid lowering medications, and with an overall Framingham risk score of ≤10%. Intervention: Participants were required to consume sufficient milk to provide 25 g protein/d from each source. The protocol included three 4-week treatment phases, each separated from the next by a wash-out period of ≥4 weeks. Results: Mean LDL-C concentration at the end of each phase (± SD) was 161 ± 20, 161 ± 26 and 170 ± 24 mg/dL for the whole bean soy milk, the soy protein isolate milk, and the dairy milk, respectively (p = 0.9 between soy milks, p = 0.02 for each soy milk vs. dairy milk). No significant differences by type of milk were observed for HDL-cholesterol, triacylglycerols, insulin, or glucose. Conclusion: A 25 g dose of daily soy protein from soy milk led to a modest 5% lowering of LDL-C relative to dairy milk among adults with elevated LDL-C. The effect did not differ by type of soy milk and neither soy milk significantly affected other lipid variables, insulin or glucose.