WINSTON-SALEM, N.C. -- The cholesterol-lowering effect of soy depends on the amount of isoflavones --plant estrogens--in the soy, according to a study at Wake Forest University Baptist Medical Center. Soy high in isoflavones can lead to dramatic drops in cholesterol.
Soy from which the isoflavones had been extracted does not lower cholesterol, nor does a relatively low dose of isoflavones in soy protein, said John R. Crouse, III M.D., writing in the current Archives of Internal Medicine.
"Our study does not allow us to define which of the many component isoflavones in soy protein may lower cholesterol," said Crouse, professor of internal medicine (endocrinology and metabolism) and public health sciences.
He conducted a nine-week study that assigned participants to eat soy protein containing one of four amounts of isoflavones, ranging from a low of 3 milligrams of isoflavones (most of the isoflavones had been extracted) to a high of 62 milligrams, or a milk protein placebo.
The results were dramatic in the 62 milligram group. In just nine weeks, the low-density lipoprotein (LDL) cholesterol levels dropped by 10 percent in those patients whose LDL levels were greater than 164 mg/dl, a moderately high level. LDL is the bad cholesterol that doctors believe elevates the risk of heart disease. In the same group, total cholesterol dropped by 9 percent.
When all patients who got the 62 milligrams dose were consolidated (including those whose LDL was closer to normal), LDL cholesterol still dropped by 6 percent in the nine weeks, and total cholesterol dropped by 4 percent. All of these declines were statistically significant.
Patients in the high LDL group who got soy containing 37 milligrams of
isoflavones also showed steep drops of 8 percent in both LDL and total
cholesterol, but when all the patients who got 37 milligrams were grouped
together, the results were not statistically significant.
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Wake Forest University Baptist Medical Center