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NEW YORK (Reuters Health) - Estrogen-like compounds in soy known as isoflavones cannot, on their own, improve blood sugar control or reduce heart disease risk factors in postmenopausal women with type 2 diabetes, UK researchers report.

This suggests that soy's heart-healthy effects are likely due to soy protein or some dual effect of soy protein and isoflavones, Dr. Susana Gonzalez of the University of Hull and colleagues conclude in a report in Diabetes Care this month.

In a previous study, the research team found that soy protein plus isoflavones improved blood sugar control, cut insulin resistance, and reduced cholesterol levels in postmenopausal, diabetic women.

To tease out which soy components were responsible for the effect, Gonzalez and her team had 26 women with type 2 diabetes, all of whom were postmenopausal, consume a preparation containing 132 milligrams of soy isoflavones or a placebo for 12 weeks. After a four-week "washout" period in which the women didn't take placebo or isoflavones, they were switched to the opposite preparation for an additional 12 weeks.

There was no difference in blood sugar control, insulin resistance, triglycerides, or "good" HDL or "bad" LDL cholesterol levels when the women were on the isoflavones versus when they were taking placebo, the researchers report.

It's possible, they note, that the effect of the isoflavones on heart health was too subtle to be detected over a three-month period.

But soy protein itself has been shown to substantially cut levels of "bad" LDL cholesterol, total cholesterol, and triglycerides, Gonzalez and her colleagues point out. The US Food and Drug Administration recommends that people consume 25 grams of soy protein daily to reduce heart disease risk.

The current findings suggest, they conclude, "that either the soy protein component alone or a synergistic effect between the protein with the isoflavones may be responsible for any cardiovascular disease changes."

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