Mechanisms
Soy protein doubles Lp(a), but alcohol-extracting it eliminates the effect, a crossover trial of 12 people (Arterioscler Thromb Vasc Biol 2002)
Original title: Alcohol-extracted, but not intact, dietary soy protein lowers lipoprotein(a) markedly
This crossover trial tested whether alcohol-removable components of soy protein explain its Lp(a)-raising effect, having previously found soy protein raises Lp(a) more than casein. Twelve normolipidaemic men and women consumed casein, soy protein, or alcohol-extracted soy protein liquid diets for 32 days each, separated by washout periods. Median Lp(a) was more than twofold higher after 28-32 days on soy protein than on extracted soy protein (P<0.001), while casein and extracted soy protein produced virtually identical Lp(a) levels. Switching from a self-selected diet to soy protein raised median Lp(a) by 16% after 1 week (P<0.01), before declining toward baseline, whereas extracted soy protein and casein diets never raised Lp(a) and instead lowered it by more than 60% below baseline by 28-32 days (P<0.001 and P<0.01, respectively). LDL cholesterol did not differ across the three diets. The findings show dietary soy protein raises Lp(a), an effect eliminated by alcohol extraction, and that high Lp(a) can be markedly reduced through diet.
Original abstract
We previously found that dietary soy protein produces higher lipoprotein(a) [Lp(a)] plasma concentrations than does casein. This study tested the hypothesis that soy protein contains Lp(a)-raising alcohol-removable components. Twelve normolipidemic women and men consumed, in a crossover design, liquid-formula diets containing casein, soy protein, or alcohol-extracted soy protein. Dietary periods of 32 days were separated by washout periods on self-selected diets. Fasting lipid and Lp(a) levels were measured throughout. Median Lp(a) concentration was >2-fold greater after 28 to 32 days on a soy protein diet than after an extracted soy protein diet (P<0.001). Lp(a) concentrations after casein and extracted soy protein diets were virtually identical. Women and men responded similarly. When the switch was made from a self-selected to a soy protein diet, median Lp(a) concentration increased 16% after 1 week (P<0.01) and subsequently decreased toward baseline; extracted soy protein and casein diets never exhibited increased median Lp(a) levels, and after 28 to 32 days, these levels were decreased >60% below baseline (P<0.001 and P<0.01, respectively). Low density lipoprotein cholesterol concentrations were not different after the 3 experimental diets. The data indicate that (1) dietary soy protein can increase Lp(a) concentrations, (2) this effect is eliminated after alcohol extraction, and (3) high Lp(a) concentrations may be markedly reduced by diet.
Summary written by lp-a.org from the published abstract; figures as published. Page updated 18 August 2026. Methods.