The study, which was published in the Journal of Clinical Endocrinology and Metabolism, noted that a soy-rich diet showed healthy changes in the blood-fat levels of female monkeys. However, human tests yielded mixed results. So the researchers checked the blood levels of 483 women for both daidzein and another plant estrogen called genistein. About 80 percent of the women tested were postmenopausal. All were considered at-risk for heart diease.
The study produced evidence that daidzein causes soy's beneficial effects on blood-lipid levels, although additional research is required to confirm the results. Higher levels of daidzein in the blood were connected to lower levels of triglycerides and higher levels of HDL ("good") cholesterol in the participants.
Women with low estrogen levels gained the most benefit from the effects of daidzein, displaying reductions in LDL ("bad") cholesterol and lower total cholesterol, leading researchers to conclude that the soy component helped restore healthier blood-fat levels by acting like additional estrogen in the body.
"These and prior studies suggest that cardiovascular risk-reduction strategies in women should consider dietary intake of food products, such as soy, which elevate blood daidzein levels, consistent with recent recommendations," Merz and colleagues wrote.