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Soy protects heart without disrupting hormones: Study

University of Toronto

Adding soy foods to a healthy diet reduces the risk of heart disease without stimulating harmful hormone activity, according to a new study in the journal Metabolism.

Some people have been discouraged from eating soy because of claims that the estrogen in it may produce dangerously high levels of hormones in the body, says Professor David Jenkins of the University of Toronto's department of nutritional sciences and the Clinical Nutrition and Risk Factor Modification Centre, St. Michael's Hospital. "The concerns have been whether soy estrogen might lead to hormone-dependent breast cancer or abnormal sexual development in children, yet we found no evidence to support this."

The study involved two groups of people put on a low-fat diet over two one-month periods - one diet with soy foods and the other without. To determine the estrogen level resulting from each diet, the researchers collected urine for 24 hours from all the participants at the end of each month and tested it on human breast cancer cells. Since estrogen stimulates breast cancer cells to produce a special protein, the researchers measured the amount of this protein produced by each urine sample to calculate how much estrogen was present.

The total estrogenic activity in the urine of women on soy was actually slightly less than before they started the diet. "This finding suggests that soy may not have the estrogenic effects that were thought to alleviate menopausal symptoms but it refutes claims about its purported hormone risks," Jenkins says.

The study also discovered that soy reduces the risk of heart disease by lowering levels of oxidized cholesterol, which is taken up more rapidly by coronary artery walls to form dangerous plaques. Jenkins' previous research has already shown that soy consumption reduces cholesterol in general while also decreasing the amount of "bad" (LDL) cholesterol in the body and maintaining the amount of "good" (HDL) cholesterol. According to Jenkins, this confirms that soy should be promoted for its important role in preventing heart disease without fear.

Funding for this study was provided by the University-Industry Research Partnership Program of the Natural Sciences and Engineering Research Council, the Ontario Ministry of Agriculture, Food and Rural Affairs and Loblaw Brands, Toronto.


Steven de Sousa
U of T Public Affairs
(416) 978-5949

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