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News Release

November 08, 2006

U of G Researchers Debunk Soy Detriments

There have been some mixed messages lately about the dangers of consuming too much soy, but University of Guelph researchers say that making soy products a regular part of a balanced diet will only improve your health. Nutritional sciences professor Alison Duncan will discuss the benefits of eating soy Nov. 11 at 5 p.m. at the Royal Agricultural Winter Fair at Exhibition Place in Toronto.

News coverage in the past few months has linked soy to health problems, including thyroid damage and reproductive difficulties, because of the hormone estrogen that’s found in soy.

Prof. Istvan Rajcan, a soybean breeding expert in the Department of Plant Agriculture, said the misconception occurred because isoflavones — non-nutritive, naturally occurring plant chemicals found in soybeans — are related to estrogens.

“The isoflavones in soybeans are a thousand times less potent than estrogen, so one would have to consume huge amounts of soybeans to have any estrogen effect,” he said. “A small percentage of the population has food allergies to soy, but I have yet to see a study showing that an adult was negatively affected from consuming too much soy.”

Rather than doing people harm, soy isoflavones are known to offer some protection against hormone-related disorders, including certain forms of cancer, said Rajcan. “Isoflavones have been shown to reduce prostate, breast and colon cancer; to slow the onset of osteoporosis; and to alleviate symptoms of menopause.”
Added Duncan: “In the research studies that I’ve done so far, I haven’t observed any negative effects of consuming soy.”

In her study of the effects of consuming soy protein on reproductive hormones related to prostate cancer risks in healthy adult men, Duncan found that some hormones changed in a direction beneficial for prostate cancer risk. The research, published in the Journal of Nutrition, also found that hormone levels remained within normal levels, not suggesting any negative effects related to male fertility.

Duncan is also looking at the impact of soy on circulating thyroid hormones. “My research found no effects from soy consumption on thyroid hormones among healthy young men, which adds to results from other studies that had similar findings,” she said.

“Overall, foods made from soybeans have many healthy attributes,” she said. “They are often high in protein, low in fat and high in fibre.” Added Rajcan: “Soybeans produce one of the healthiest vegetable oils, and soy protein has all the essential amino acids. It has a good balance of fatty acids and a relatively small amount of saturated fat. Soybeans are also one of the main sources of vitamin E, which is a byproduct of processing the oil from soybean seeds.”

The U.S. Food and Drug Administration has approved a health claim for soy foods stating that 25 grams of soy protein a day may reduce the risk of heart disease.

“A health claim in the United States would not be approved unless there was sufficient evidence to support its validity,” said Duncan. “Canada’s Food Guide stresses moderation and variety as key concepts to a healthy diet, and soy foods have many excellent attributes that fit into that recommendation.”

In a study recently published in the American Journal of Clinical Nutrition, she found that soy protein can reduce blood fats in healthy men in a direction that reduces the chances of cardiovascular disease.

“That study showed that it’s never too early to start incorporating soy into a balanced diet and that there are benefits even for people who are healthy,” she said.