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Your Questions on Soy and Breast Cancer Answered

Soy usesFrom milk to meat substitutes, soy foods have made their way into snacks, burgers and breakfasts. That’s good news if you’re working to eat healthier and cut down on red and processed meats, which can increase risk of colorectal cancer. Yet soy is among the top foods we get asked about the most when it comes to breast cancer.

It’s no surprise women are confused with recent headlines and old studies causing any well-read woman to scratch her head. And while there’s still a lot to learn, there’s now a body of consistent and solid research behind soy and breast cancer.

Here are some basic questions you might be wondering.

What’s the bottom line for breast cancer: will soy foods increase or decrease my risk?

For breast cancer risk among cancer-free women, studies show that eating a moderate amount of soy foods does not increase risk of this cancer or any other cancer type. Some research indicates it may offer modest protection against breast cancer: These protective effects may primarily come from consuming soy during childhood and adolescence.

I’m a breast cancer survivor, is it safe for me?

The body of research shows that for breast cancer patients and survivors, consuming moderate amounts of soy foods does not increase a woman’s risk for recurrence or earlier death.

So what’s a moderate amount of soy?

A moderate amount of soy is one to two standard servings daily of whole soy foods, such as tofu, soy milk and edamame. Studies have demonstrated as many as three servings of soy foods a day are not associated with increased breast cancer risk.

Why have I heard soy may increase breast cancer risk then?

Soy contains compounds called isoflavones, which are classified as plant estrogens. High levels of estrogen link to increased risk of breast cancers. Early animal studies saw that high amounts of two isoflavones – genistein and daidzein – promoted breast cancer growth. Scientists now know that rodents and most other lab animals metabolize soy isoflavones differently than humans.  And soy consumption does not lead to increased estrogen levels in humans.

But just recently I’ve heard that soy promotes breast cancer - what’s that about?

You probably saw headlines about a new study that focused on soy supplements - not soy foods. This study among women diagnosed with breast cancer was short, only 7 to 30 days. The women who ate soy powder had changes in certain genes that play a role in breast cancer growth. But there were also changes to other genes so it is unclear what the end effect would be (and if this only affects certain women), and tumor cell growth was no different than in a placebo group . And the amounts of isoflavones consumed were far above – about double – what you would get from food if you were to eat one to two servings every day.

I see soy in the ingredients of so many foods I eat. Does that add up to more than what’s considered moderate?

Not likely. Most cereals, bars and other products with a soy concentrate in them have a relatively small amount of isoflavones. You would have to eat about 7 soy bars a day – without any other soy products – to get to the upper amount of what is recognized as safe. (Our nutrition advisor Karen Collins has done some digging to find out how much isoflavones different products contain.)

If there’s any concern, why should I eat soy?

There’s a lot of tasty – and healthy – soy foods out there. Soy foods can be a great way to get plant-based protein (and in some cases,  more calcium), along with other healthful compounds. They’re good sources of protein, and many are also good sources of fiber, potassium, magnesium, copper and manganese.

I’ve never even had tofu. What do you do with soy?

Visit our Foods that Fight Cancer section to find tips and recipes for soy foods.

Published on 10/02/2014

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