Is It Safe to Eat Soy?

Lately there has been some controversy about safety versus the benefits of soy foods. We are told that soy foods can help to fight heart disease, make your bones stronger, and contain cancer-fighting compounds, but there are also allegations that soy foods also raise cancer risk, cause nutrient deficiencies, osteoporosis, thyroid problems, reproductive difficulties, and Alzheimer's Disease.

What’s a vegan to do?

I found an article By Virginia Messina, MPH, RD & Mark Messina, PhD at, veganoutreach.org that, I think, sheds some light on this controversy. Here are some highlights from the article. Please go to http://www.veganoutreach.org/health/soysafe.html for the full article.

" Many of the studies that have concluded that soy is unhealthful have used animals as subjects. Drawing conclusions about human health from animal research can be very misleading. For example, broccoli and other cruciferous vegetables contain a compound (called indole-3 carbinol) that is an anticarcinogen in humans. But in some other species, it causes cancer. If we looked only at the results of the studies in those species, the FDA would no doubt ban broccoli and cabbage from grocery stores."

"Many foods contain goitrogens, compounds that interfere with thyroid function (and in extreme cases can cause an enlarged thyroid, called a goiter). Along with soyfoods, millet, cruciferous vegetables and other foods contain goitrogens. Generally, these foods cause problems only in areas where iodine intake is low since this mineral is important for thyroid function. The effects of iodine deficiency can be made worse if the diet is high in goitrogens."

"There is no evidence that eating soyfoods regularly causes thyroid problems in people who eat a balanced diet. Vegans should make an effort to include adequate sources of iodine in their diet."


"One study has suggested a link between tofu consumption and poorer cognitive function in old age, but this is an epidemiological study. Therefore it doesn't show cause and effect. It did not look at diet extensively enough to draw firm conclusions. And there are no other studies to support it and three clinical studies suggest soy and isoflavones have beneficial effects on cognition. At this point, there is no reason to believe that eating soyfoods is harmful to brain aging."

"Soyfoods can be good sources of well-absorbed calcium whether they are natural sources of this mineral or are fortified with it. They may also provide other factors that help to improve bone health. Vegans should make sure their diets are adequate in calcium and vitamin D and are generally well-balanced with adequate protein. Iron deficiency does not appear to be a problem for vegans--at least no more so than for people eating other kinds of diets. But, given that it is a common world-wide deficiency, everyone should make sure they eat plenty of iron-rich foods and vegans should consume good sources of vitamin C at meals. Likewise, it is important to eat plenty of zinc-rich foods every day"

"At this time, there seems no reason for women who have had breast cancer to avoid moderate consumption of soy. And for women who have never had cancer, there seems no reason to restrict soy."

"Although soy isoflavones have weak estrogen-like effects, there is no evidence of reproductive problems in those who eat these foods."

"Based on the bulk of the evidence soy appears to be perfectly safe for nearly all healthy individuals when it is consumed in reasonable amounts. We would say that a reasonable amount of soy is two to three servings per day. Women who have had estrogen-positive breast cancer may want to be somewhat more restrictive in their soy intake but, if they are already eating and enjoying soyfoods, there is not enough evidence of any harmful effects to suggest that they need to avoid all soy."

About the Authors
Virginia Messina, MPH, RD is an adjunct assistant professor at Loma Linda University and a consultant on vegetarian nutrition. Mark Messina, PhD is an adjunct associate professor at Loma Linda University and an expert on soy and chronic disease. He is a consultant for numerous health professional organizations and for the soy industry.