SAN FRANCISCO - April 4, 2000 (Reuters) -- Soy consumption has been shown to inhibit breast cancer, but isoflavones -- a soy component assumed to provide those anti-cancer benefits -- may not be that important, a study presented on Monday.

The study casts doubt on the benefits of using purified soy isoflavones to cut the risk of breast cancer.

Researchers at the University of Illinois at Chicago (UIC) tested purified isoflavones against soy protein mixes with and without isoflavones in female rats to determine their effectiveness in reducing the incidence and the number of mammary gland tumors.

"There are well-established studies showing that soy is effective in helping prevent tumors. The assumption was that isoflavones would be the active ingredient, but we found a lot of surprises," Dr. Andreas Constantinou, associate professor in surgical oncology at UIC's College of Medicine, said at an American Association of Cancer Research meeting here.

Although all the compounds studied reduced the incidence of tumors, the soy protein mix without isoflavones was the most effective in decreasing the number of tumors, he said.

Constantinou suggested that the anti-tumor ingredient in the soy mixture works by increasing the production of two detoxification enzymes that shield cells from harmful substances called free radicals.

Other components of soy that could be responsible are dietary fiber, phytic acid or lignans, the researcher said.

Purified isoflavones have become commercially available as women at risk for breast cancer seek preventive measures against the disease.

Studies have shown an inverse relationship between the consumption of soybean products and breast cancer risk in premenopausal women. In addition, the incidence of the disease is lower in Japan and regions of China -- where a large percentage of daily caloric intake is from soybeans -- than in Western industrialized countries where little or no soy is included in the diet.

"Based on these findings, I recommend against using purified soy isoflavones," Constantinou said.

reprinted from http://www.cnn.com/2000/HEALTH