Soy and Your Health: Dispelling the Myths Part 3

Review of article by Dr. Messina, an expert in the study of soy.
Breast Cancer
For more than 20 years the US National Cancer Institute and laboratories throughout the world
have been rigorously investigating the role of soy in breast cancer prevention. However, in
recent years, concerns have arisen that, because they contain isoflavones, soyfoods may worsen
the prognosis of women with a history of breast cancer and increase risk of breast cancer in women at high risk of developing this disease. These concerns are based on research in one particular type of mouse. Because rodents metabolize soy much differently than humans, they aren’t particularly useful models for learning about the effects of soyfoods. Studies done with humans paint a different picture. When female subjects are given either soyfoods or the isoflavones from soyfoods, there is no effect on indicators of breast cancer risk. Recently published studies from China and the United States, show that soy consumption after a diagnosis of breast cancer reduces recurrence and improves survival.

Soyfoods and Male Reproduction
The estrogen-like effects of isoflavones have led to concerns that soyfoods may exert feminizing
effects in men, but a wealth of human data show these concerns to be without merit. A recent review of
nine studies found that soy has no effect on estrogen levels in men. Men in these studies consumed as much as six servings of soy per day.

Thyroid Function
Although soy isoflavones can interfere with thyroid function in laboratory animals, they have no
effect on thyroid activity in healthy people. More than 20 studies have examined thyroid
function in response to the consumption of soyfoods, soy protein, or isoflavones. The evidence overwhelmingly supports the safety of soy.

Cognitive Function
In a study conducted in Hong Kong, tofu had no effect on cognition, and in Indonesia, intake of the widely consumed soyfood tempeh, was linked to better cognitive health whereas tofu was unrelated. Even more important, the clinical studies, which are studies in which subjects are actually given the test product, suggest that soy may improve cognitive function. At this point, the totality of the evidence suggests
soy may actually improve cognitive function, not impair it but the data are far too limited for any
claims about the impact of soy on cognition to be made.

Consumption
There is a considerable range of soyfood intake among Asian countries. In Japan and some urban
areas of China, average consumption is around 1 ½ to 2 servings per day, but older people with
more traditional diets may consume as many as 3 servings per day of 25 grams. Both fermented and
unfermented soyfoods are popular throughout Asia. While consuming more than this amount is not unsafe, consuming too much (more than 4 servings in one day) of any food violates the principles of moderation and variety.