Lipoprotein(a) and dietary proteins: Casein lowers lipoprotein(a) concentrations as compared with soy protein

Abstract

Background: Substitution of soy protein for casein in the diet decreases LDL cholesterol and increases HDL cholesterol. How the 2 proteins affect lipoprotein(a) [Lp(a)], an independent risk factor for coronary artery disease, is unknown. Objective: We compared the effects of dietary soy protein and casein on plasma Lp(a) concentrations. Design: Nine normolipidemic men were studied initially while consuming their habitual, self-selected diets, and then, in a crossover design, while consuming 2 liquid-formula diets containing either casein or soy protein. The dietary periods lasted 45 d (n = 7) or 33 d (n = 2). Fasting total cholesterol, LDL- cholesterol, HDL-cholesterol, triacylglycerol, and Lp(a) concentrations were measured throughout. Results: After 30 d of each diet, the mean concentration of Lp(a) was not significantly different after the soy-protein and self- selected diets. However, Lp(a) decreased by an average of 50% (P < 0.001) after the casein diet as compared with concentrations after both the soy- protein and self-selected diets. Two weeks after subjects switched from the self-selected to the soy-protein diet, Lp(a) increased by 20% (P = 0.065), but subsequently decreased to baseline. In contrast, the switch to the casein diet did not cause an increase in Lp(a), but instead a continuing decrease in mean concentrations to 65% below baseline (P < 0.0002). Total cholesterol, LDL cholesterol, and HDL cholesterol were significantly lower ≥30 d after both the casein and soy-protein diets than after the self-selected diet (P < 0.001). HDL cholesterol was 11% higher after the soy-protein diet than after the casein diet (P < 0.002), but LDL cholesterol, total cholesterol, and triacylglycerol were not significantly different after the casein and soy- protein diets. Conclusion: These findings indicate that soy protein may have an Lp(a)-raising effect, potentially detrimental to its use in antiatherogenic diets.