Gabe Mirkin, M.D.

There are so many articles on how soybeans can improve health that 
some people eat soybean products at every meal. You shouldn't do 
that because too much of anything can be harmful. Mary Enig has 
written a very thought-provoking article about soybeans (1), and 
while I don't agree with a lot of her conclusions, it does underline 
the risk of eating too much of any food. 

You have heard us say many times that plants contain chemicals that 
make us healthy and chemicals that can harm us. Fortunately for us, 
our ancestors picked out plants that contain more good chemicals and 
therefore are healthful, and taught us to avoid those that are 
poisonous. However, if you eat large amounts of one food, you can 
poison yourself, even though reasonable amounts are harmless or 

An example is soybeans. Soybeans contain genistein, a weak estrogen 
that may help to prevent breast cancer. They contain omega-3 fatty 
acids that help prevent heart attacks, and are loaded with fiber 
that helps to prevent diabetes.

But soybeans contain trypsin inhibitors that block protein 
consumption and hemagglutinin that causes clots to form. It you take 
in huge amounts of soybeans, you increase your risk for pancreatic 
damage and even pancreatic cancer because the trypsin inhibitors 
block protein use and therefore make your pancreas work too hard to 
overcome this effect. Huge amounts of soybeans can also make clots 
that can form in your heart or lungs. Soy contains goitrogens that 
block thyroid function. In small doses these goitrogens do not harm 
you, but large doses can slow your thyroid. Soybeans (and many other 
plants) also contain phytates, which can block the absorption of 
minerals. Nobody has shown that phytates in soybeans are harmful; 
this is a theoretical concern. 

Dr. Enig is particularly concerned about the widespread use of 
infant formula made from soybeans. We have no data yet on the 
consequences of feeding plant estrogens to small children. If you 
choose to use feed you baby soy milk, cow's milk or any formula 
other than breast milk, I recommend that you introduce other foods 
as early as possible to add variety to the diet and reduce your 
infant's reliance on any single food.

When you hear about the health benefits of any food, don't believe 
that you should start eating it to the exclusion of other foods. 
Huge amounts of any single food can be harmful. A healthy diet 
contains a WIDE variety of fruits, vegetables, whole grains, beans, 
nuts and other seeds; and modest amounts of any foods you enjoy. 

1) Fallon, Sally, and Mary G. Enig, PhD, Tragedy and Hype: The Third 
International Soy Symposium, Nexus Magazine, Volume 7, 
No. 3(April-May 2000).