Can Soy Cause Breast Cancer?

by Natalie on May 30, 2012

Confused about soy and breast cancer? You’re not the only one. Researchers have been studying soy and breast cancer for decades and still don’t have all the answers!

The good news is that with all the research being done, we now have a much clearer picture of the soy/breast cancer relationship.

Before we proceed: the topic of soy and breast cancer is extensive and cannot be covered completely in one single blog post. My goal in this article is to cover a few key points.

Why All the Confusion?

Interestingly, soy was first studied for its protective role against breast cancer. In these early studies, Asian women who traditionally consumed higher amounts of soy were seen to have lower rates of breast cancer.

The controversy began when researchers brought the study of soy out of people and into the laboratory. Studies done in lab animals and test tubes showed that soy actually promoted the growth of breast cancer cells.

So what gives? Why did the studies in people show a protective effect and the lab studies show a harmful effect?

We now believe it has to do with the type of soy being used in research. In the human studies, most of the women were eating traditional whole soy foods. In the lab studies, highly concentrated soy products were used in amounts much greater than women would traditionally eat. From this knowledge researchers determined that consuming processed soy or soy supplements may be harmful for women, especially women at high risk of breast cancer or those with breast cancer.

It is best to consume whole (minimally processed) soy foods and avoid processed soy foods and supplements. Studies done in large populations of people continue to assure us of the safety of consuming whole soy foods.

Examples of  Whole Soy Foods

  • whole soybeans
  • edamame
  • roasted soybeans
  • soy milk
  • tempeh
  • tofu
  • miso

Examples of Processed Soy Foods

  • soy shakes
  • soy chips
  • soy bars
  • soy supplements
  • soy powders
  • fake meat products

If the product is questionable, read the label. If the ingredient list has any of the follow words “soy protein concentrate”, “soy isolate”, or “isolated soy protein”, avoid the product.

How Much is Safe to Eat?

The active compounds in soy are called isoflavones. Isoflavones have a structure similar to human estrogen and can act like a weak form of human estrogen. It is still unclear whether or not this is a good thing. In some cases it appears to be good and in others it appears to be bad. This is why it is a good idea to be conservative with your soy intake.

Small amounts of whole soy foods appear to be completely safe – maybe even protective against breast cancer, but too much may be harmful.

1 to 2 servings of whole soyfoods per day are safe and healthy for most women to consume.

Soy Serving Sizes

  • 8 oz soymilk
  • 3.5 ounces of tofu or tempeh (about the size of the palm of your hand or a deck of cards)
  • ¼ cup roasted soybeans
  • ½ cup cooked soybeans or edamame

You don’t need to consume soy to be healthy, but know that it can be safely included in your breast cancer prevention plan if you want to eat it. Just make sure you choose whole, minimally processed soy foods and keep it to 1 or 2 servings each day.

I would love to hear what you think! In the comments below, tell me:

1. If you have ever felt confused by the soy/breast cancer relationship.

2. What would help make the confusion go away?

photo by: the 10 cent designer on Flickr

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Nancy Walsh November 5, 2012 at 3:48 pm

I have been reading multiple sites trying to find a concise or clearly written article for recommendations on what specifically to avoid on the nutrition labels for people with breast cancer. Everything has soy something in it, Is there a specific resource I can access or print to take to the store with me. I am very confused on what is considered safe to eat or not.For example is powdered coffee creamer safe to use? Thank you for any help you can send me.

Natalie November 15, 2012 at 2:08 pm

Thank you for your comment Nancy. I am sorry that you have not been able to find what you are looking for. You’re right, a lot of processed foods contain something soy. As I stated in my article, it is most important that you avoid foods with “isolated soy protein” or “soy protein isolate” or “concentrated soy protein”. Whole soy foods are okay to consume in moderation (1 to 2 servings per day). I do know of a resource, but it is by no means concise. It is a database from the USDA on isoflavones of common foods. With it, you can look up the amount of isoflavones in foods. If you are interested, here is the link. Hope this helps!

Natalie November 15, 2012 at 2:11 pm

Forgot to respond to your question on powdered coffee creamer. I do not recommend these products because they are usually made with hydrogenated oils (trans-fats). Coffee-Mate just came out with a liquid creamer that is made without hydrogenated oils, it is called “Natural Bliss”.

Nicole Aboujaoude February 1, 2013 at 4:39 am

I’m a vegetarian (almost vegan, still eat cheese & milk chocolate) who relies very heavily on the fake meats like Tofurky. My boyfriend and I started switching between soy and almond milk to avoid too much soy intake. I’ve been paranoid about breast cancer for a while, because my mother and grandmother both had it. Though the doctors say it wasn’t genetic, and both survived, I am obviously still concerned, so when I recently heard rumors about soy, I started searching the web frantically.

First off, I’d like to thank you for a clear article- one of the few I’ve seen that makes a mostly clear, concise conclusion. But I was just wondering, since I still have a fridge full of these fake meats, do you think limited consumption of these might be safe? Or are they so awful that any meal I make with them is a serious threat to my health? I’m worried to cut them out completely, because I’m a college student, so most times they are the easiest foods to cook with when I’m busy with school work.

I appreciate your help!

Natalie February 6, 2013 at 12:16 pm

Hi Nicole,

I am glad you found the article helpful. Now to answer your questions: First, check the ingredients list of your “fake” meat products. If they don’t contain any soy protein isolate or isolated soy protein or soy protein concentrate, then go ahead and continue eating them. If they do contain ISP, I don’t think you need to waste them. I would go ahead and finish them up, but in the future, look for products that don’t contain ISP or soy concentrate. At this time, I don’t really think there is a safe level to consume, especially with a family history of breast ca.

Sunshine Burger is a brand of veggie burgers that don’t contain any soy. Consider looking for that brand. Also, tempeh is a whole form of soy and a better option. There are flavored versions of tempeh that you can use to make a sandwich or put on salads. Consider experimenting with that. Amy’s is another brand that offers some convenience food items you should check out. The breakfast burritos are tasty and don’t contain and isolated soy protein.

Hope this helps!

Steffie May 6, 2013 at 8:39 am

I would also recommend Quorn products which are totally soy free. I’ve tried the “chicken” patties and nuggets and they are really good. They sell a bunch of other products like “meatballs” etc but I haven’t tried them. Hope this help.

Thanks you Natalie for your clear and informative article!!

Natalie May 8, 2013 at 9:18 pm

Thanks for sharing Steffie. I haven’t tried Quorn, but will check it out soon.

miyoko schinner April 18, 2013 at 1:11 pm

Tofurky is made from gluten and tofu, a whole soy food, and does not contain isolated soy protein.

Elaine June 2, 2013 at 9:12 pm

Hi Natalie,

Loved your article very helpful. I take Michelle Bridges protein figure shake once a day after excersise. It has 21.2 g of soy protein per serve. Is this safe or shall I stop taking it?
Is whey protein better?

Thanks for your page..

Natalie June 3, 2013 at 1:26 pm

Hi Elaine,

Thanks for your comment. I am glad you found the article helpful. I recommend avoiding isolated soy protein because this is the type that may promote breast cancer development. I think it is a good idea to stick with a non-soy plant protein powder such as from hemp, pea, rice or a combination of all three. I am currently using Sun Warrior “warrior blend” protein powder.

Liz May 5, 2013 at 5:38 am

Hi Natalie, thank you for the article it’s really helpful. Is ‘textured soya protein’ the same as the bad types of soya you listed?

diana June 10, 2013 at 1:46 pm

my sister has breast cancer ans does not know what to eat
she has bought food likem orning star with soy in it
is this safe
this soy things is very confusing

arun June 26, 2013 at 10:53 pm

can u tell me other foods ,expect soy,to take eat make breast cencer…

Natalie June 27, 2013 at 9:16 am

Hi Arun, I think you are asking about which other foods could increase breast cancer risk. I think you will find this post helpful – it’s titled, Foods to Avoid with Breast Cancer. I hope this is the info that you are looking for.

Barbara B September 3, 2013 at 7:00 pm

Wonder if you know the answer to the question I sent a few days ago. Is taking Vitamin K supplement which includes Natto (soy) not good because of the soy for someone who has a family history of breast cancer. If not do you know where to look for that information? Thanks, Barb

Natalie September 12, 2013 at 12:59 pm

Hi Barb, thanks for your question. Unfortunately there is not a black or white answer. The soy/breast cancer controversy still runs deep. Based on my research, I have found that processed soy products (containing isolated soy protein) should be avoided. Natto is a whole soy food, made from fermented soybeans. Whole soy foods are better to eat than processed, but they still contain soy isoflavones. Small amounts of soy isoflavones are okay for women with an increased risk of breast cancer, but too many could be problematic. In my professional and personal opinion (being at increased risk of breast cancer myself), I would not take a soy product daily.

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