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Experimental evidence was sought concerning whether soy phytoestrogens (SPEs) inhibit postmenopausal atherosclerosis progression/extent and, if so, their effectiveness relative to traditional estrogen replacement therapy. Premenopausal cynomolgus monkeys were fed a moderately atherogenic diet (26 months) to induce atherosclerosis. After ovariectomy, the moderately atherogenic diet was continued, and they were treated (36 months) with a control diet (soy protein depleted of SPEs), a diet containing SPEs in soy protein isolate, or a diet containing SPE-depleted soy protein with conjugated equine estrogens (CEE; Premarin) added. SPE effects on plasma lipids were better than those of CEE (higher high density lipoprotein cholesterol and no increase in triglyceride). Relative to the control group, CEE treatment inhibited (P = 0.0001), and SPE treatment partially inhibited (P = 0.10) the progression of atherosclerosis (common iliac artery atherosclerosis before and after treatment). CEE-treated monkeys had much less coronary artery atherosclerosis than the controls (P = 0.0002), whereas SPE-treated monkeys were intermediate in lesion extent between the controls and the CEE-treated animals (P = 0.02). Both CEE and SPE significantly reduced the extent of common carotid and internal carotid artery atherosclerosis, and the two treatment groups were not significantly different.
Clarkson et al. (Mon,) studied this question.