April 22 (HealthDay News) -- Soy isoflavones don't increase breast density, a new study finds.

That's good news because it's believed that increased breast density is associated with a higher risk of breast cancer. A number of studies have suggested that dietary factors, including isoflavones (estrogen-like plant compounds) might increase breast density. However, there have been mixed findings about the link between isoflavone intake and breast density, according to background information in the new study.

It included 358 postmenopausal women who averaged 55 years old. Each day for two years, they took either a placebo or one of two dosages -- 80 milligrams or 120 milligrams -- of soy isoflavones, contained in soy-germ isoflavone tablets. The soy dosage levels are equivalent to the amount of isoflavones provided in two to four cups of soy milk.

Breast tissue assessments, done during and at the end of the study, indicated that soy isoflavone consumption had no effect on any breast tissue measurement, including density. The findings did not change after the authors factored in age and obesity.

"These findings offer reassurance that isoflavones do not act like hormone replacement medication on breast density," the researchers concluded.

The study appears in the May issue of the Journal of Nutrition.

SOURCE: Journal of Nutrition, news release, April 14, 2009