Scared of soy? Thanks to internet and TV claims, many people have a fear of this legume. But is there any research to actually support this fear? Read on to find out.

The controversy over soy has to do with the isoflavones that it contains. Isoflavones are a phytoestrogen that act as a very weak form of estrogen and actually compete for the same place on cells as estrogen. This means that they can affect the action of estrogen. They do not, however, increase estrogen levels in the body.

The isoflavone content of soy foods differs by food:

  Portion: Isolfavones:
Edamame ¾ cup 138 mg
Soybeans, cooked ¾ cup 81 mg
Soynuts, roasted ¼ cup 60 mg
Tofu ¾ cup 52 mg
Soy beverage 1 cup 20-30 mg

The number one concern that I hear about soy products is that they increase the risk of breast cancer. However, there is no evidence to support this claim. The original research was conducted in rodents who metabolize isolfavones very differently than humans. In human population studies, soy consumption is actually associated with reduced breast cancer risk. Research shows that breast cancer survivors and even women with estrogen-sensitive breast cancers do not need to avoid soy. On the other hand, it is recommended that they don’t take soy supplements that contain concentrated forms of isoflavones.

Others fear that consuming soy may cause an underactive thyroid by blocking thyroid hormone production. In fact, this claim is only supported in people who do not get enough iodine (a mineral) in their diet. In Canada, iodine deficiency is rare because salt has iodine added to it to prevent deficiency.

Another concern with soy is a fear that it will cause feminization in men since isoflavones acts like a weak estrogen. However, this claim, like the one above, is not supported. Men would have to consume extremely high amounts of soy to cause sex hormone changes. Additionally, the effects would be reversed when soy intake was discontinued.

Soy is a great addition to the diet, especially for vegetarians or those trying to limit animal product intake. 1 cup of soy milk contains as much protein as about 100 grams of meat. Unlike other beans, such as kidneys beans, black beans, or chickpeas, soybeans are a complete protein, which means that they contain all the essential amino acids needed for growth and development.

 If you don’t consume cows’ milk, soy milk is a great alternative and should be selected over other milk alternatives like almond, cashew or rice. This is because soy milk has a similar nutrient profile to cows’ milk. Both contain about 8 grams of protein. On the other hand, almond milk, cashew milk and rice milk are all poor protein sources. Each contain only about 1 gram of protein.

Another reason to include soy protein is its positive heart health effects. Consuming 20 grams of soy protein each day reduces “bad” LDL cholesterol that can cause cardiovascular disease.

Be careful what you read online. Many people hype up the fear of soy products despite the lack of evidence to support the claims. There should be no fear when it comes to consuming soy. It’s a nutritious and tasty choice.

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Categories: Megan Kuikman

Megan Kuikman

Hello! I’m Megan Kuikman. I’m a Registered Dietitian with specialized training in sports nutrition. My goal is to help athletes and active individuals achieve a healthy attitude towards health, training, and food. I empower athletes to fuel properly for training in order to restore their health and enhance performance. You can get in touch with me at:


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