Lack of effects of isoflavones on the lipid profile of Brazilian postmenopausal women.

OBJECTIVE: To evaluate the effects of soy isoflavone supplementation on profile lipid and endogenous hormone levels.

METHODS: In this double-blind, placebo-controlled study, 47 postmenopausal women 47-66 y of age received 40 mg of isoflavone (n = 25) or 40 mg of casein placebo (n = 22). Cardiovascular risk factors were assessed by evaluating lipid profile at baseline and after 6 mo of treatment. To examine the effects of this regime on endogenous hormone levels, follicle-stimulating hormone and beta-estradiol were measured. Urinary isoflavone concentrations (genistein and daidzein) were measured as markers of both compliance and absorption using high performance liquid chromatography. Baseline characteristics were compared by the unpaired Student's t-test. Within-group changes were determined by paired Student's t-test and comparison between the isoflavone and casein placebo groups were determined by analysis of variance.

RESULTS: Lipid levels (low-density lipoprotein and total cholesterol) similarly decreased in both groups. High-density lipoprotein increased significantly in both groups and cannot thus be attributable to treatment; the reason for such variation is unknown and can be attributed to chance or to bias (even that of a real placebo effect in both groups or perhaps in spontaneous changes in exercise and dietary habits of patients after their inclusion). Furthermore, in both groups very low-density lipoprotein and triacylglycerol levels increased in a non-significant manner.

CONCLUSION: The results of the present study do not support any biologically significant estrogenic effects of isoflavone on the parameters assessed. Further research will be necessary to definitively assess the safety and efficacy of isoflavone.