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Do soy foods increase cancer risk?

Focused on Health - May 2013

by Amber Presley

Soy is on the menu at restaurants and in our markets. But what is soy and can it increase or decrease cancer risks? It’s a hot topic that’s confusing, so let’s start with the basics.

Get protein from soy

Soy is a plant protein full of fiber, potassium, magnesium and other vitamins. Popular soy foods include tofu, edamame, miso and soy milk.

“Soy contains all the essential amino acids that play a role in supporting the body’s vital functions,” says Clare McKindley, clinical dietitian in MD Anderson’s Cancer Prevention Center. “It can be an easy way for people on a vegan or vegetarian diet and those with food allergies to get those required amino acids. But, as with any food, eating in moderation is recommended.”

cancer, soy, risk, foodsA moderate amount of whole soy foods is up to three daily servings. Examples of a single serving include: 1 cup of soy milk, 1/2 cup cooked soy beans, 1/2 cup edamame or 1/3 cup tofu.

Soy and breast cancer

Because natural soy foods contain isoflavones, similar to estrogen, some people fear that soy may raise their risks for certain cancers. This is because estrogen is linked to hormonally-sensitive cancers, like breast cancer.

But according to the American Cancer Society, when it comes to soy, isoflavones may act like estrogen, but they have anti-estrogen properties as well. Some studies even show that people who ate soy were less likely to get breast cancer. 

“The current research does not support avoiding whole soy foods--even for cancer patients or survivors,” McKindley says.

READ ALSO: The pros and cons of soy

Soy might lower the risk of other cancers

Soybeans, soy nuts and edamame all contain fiber. And, a diet high in fiber may lower your risks for several cancers, including colorectal cancer.

cancer, foods, soy, risk, Studies among prostate cancer survivors indicate that eating soy foods may lower PSA levels. Among men in various stages of prostate cancer, those who consumed soy milk or isolated soy isoflavones saw their PSA levels rise at a slower rate. The effect was stronger in some men than others, making it unclear whether genetics or metabolism made a difference in lowering PSA levels.

A healthy balanced diet can include soy

It’s important to have a variety of foods in your diet, including soy.

“If you’re still uncomfortable adding whole soy foods to your diet yet want to reduce how much animal protein you eat, try these common alternatives: beans, lentils, nuts and seeds," McKindley says. "The protein (and amino acid) content will vary for each."

If you want to add soy to your diet, eat fewer processed soy foods, and choose more whole foods like edamame, tofu and soynuts. Does that mean you should skip the soy nuggets? Not necessarily. That’s a personal choice. But, remember that a processed soy nugget is just that—processed food. And, avoiding processed foods is another way to keep your cancer risks low.

If eating certain foods, like soy, gives you anxiety, skip them.

"Consider talking with a dietitian if you have questions about going meatless," McKindley says. "It's important to make sure you are getting all the nutrients your body needs. Talking with an expert will help you go in the right direction."

READ ALSO: Where's the beef? The trouble with processed food.

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© 2014 The University of Texas MD Anderson Cancer Center