We found previously that dietary soy protein, compared with casein, reduced
plasma LDL cholesterol and increased HDL cholesterol concentrations in hea
lthy women and men. However, there was considerable variation among individ
uals. The aim of this study was to characterize the lipoprotein responsiven
ess of individuals to examine whether different response patterns could be
identified. Nine normolipemic men consumed 2 liquid-formula diets of identi
cal composition except that the protein component was either soy protein or
casein. After 1 mo of consuming each diet, the subjects' plasma HDL choles
terol (P < 0.01) and apolipoprotein (apo) A-I (P < 0.05) concentrations wer
e increased by the soy-protein diet whereas the ratio of LDL cholesterol to
HDL cholesterol was decreased (P < 0.01); total cholesterol, triacylglycer
ol, LDL cholesterol, apo B and apo A-II were insignificantly affected. In 5
individuals, however, soy protein reduced mean LDL cholesterol, LDL2 chole
sterol, and LDL2 apo B concentrations by 26% and plasma apo B by 16%, where
as HDL cholesterol increased by 11%. In 3 other individuals, soy protein in
creased mean HDL cholesterol by 17% and plasma apo A-I by 12%, but did not
lower LDL. In 1 subject, soy protein decreased LDL2 cholesterol by 11% and
increased plasma triacylglycerol by 40%, but neither HDL cholesterol nor ap
o A-I increased. We identified 3 types of lipemic responses to dietary soy
protein involving a reduction in atherogenic LDL and increase in antiathero
genic HDL. In most subjects, the effects on both LDL and HDL were favorable
, although fewer experienced either an increase in HDL or a decrease in LDL
2.