Research in Monkeys Suggests Dietary Soy Does Not Contribute to Breast Cancer

There has been some speculation that natural plant estrogens found in soy might increase the risk of breast and other cancers in postmenopausal women if eaten in large enough quantities. But a recently published study of the effects of high soy diets in monkeys suggest that a high soy diet does not increase the risk of breast or uterine cancer .

As lead researcher Dr. Charles Wood notes, there has been concern about carrying out research on the high use of high soy content diets over fears that such diets might spur cancer,

Evidnece from observational studies in women indicates that soy intake may help prevent breast cancer. But there has still been reluctance to conduct research studies in women because of concerns that isoflavones may stimulate breast cell growth and increase the risk of breast cancer.

So Woods followed groups of postmenopausal monkeys who ate one of three diets for three years — either soy without isoflavones, soy with isoflavones, or soy without isoflavones but with Premarin added.

Researchers then measured a number of indicators of breast and uterine cell growth as well as estrogen levels in the bodies of the monkeys. The study found that monkeys on the soy with Premarin diet had higher levels of a number of markers for cancer, but the monkeys on the soy with isoflavones diet did not.

In a press release, Dr. Wood said,

These findings suggest that high dietary levels of soy isoflavones do not increase makers for breast and uterine cancer risk in postmenopausal monkeys and may contribute to an estrogen profile associated with reduced breast cancer risk.


Animal research suggests plant estrogens in soy do not increase breast cancer risk. Press Release, Wake Forest University Baptist Medical Center, July 6, 2004.

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