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Breast Cancer and Soy: The Truth

When it comes to soy, there’s a lot of well meaning, but misleading misinformation out there.  Let’s clear it up:


Soy and Health

Whole foods comprised of soy are a great source of calcium, protein and other nutrients. They’re extremely versatile and can be prepared in many delicious ways. But they’re not magic. They won’t directly cause weight loss, provide relief from hot flashes, and they aren’t a miracle nutrient deemed to prevent or cause disease.  

Soy is common.  Edamame and tofu are among the most obvious, and most natural forms of soy on the market.  They are a great source of protein, and are versatile when it comes to cooking.  On the other hand, Ingredients like soy lecithin is a bit more tucked away from view, but is common.  It’s often found in small amounts in dietary supplement pills and processed and packaged foods as an emulsifying agent, which helps to properly mix oil and water, and a stabilizer to prevent the food from going rancid.  Soy isolate is also used in meat analogs and as fillers.  However, Processed foods with added soy protein are still processed foods, and likely not the best for our health for a number of reasons including typically sky-high amounts of sodium and added sugars. 

Soybean oil has a higher ratio of omega-6 to omega-3 fat compared to extra virgin olive oil, but it’s not bad for you.  Since the average consumer gets a healthy amount of omega 6 in the diet compared to omega 3, it may be best to stick with olive oil for salad dressings, bread dipping, and roasting vegetables. 

When it comes to growing the vegetable, the most important concept to understand is organics.  Most soy crops grown in the United States are genetically modified unless the the USDA has specified that they are certified organic.  If GMO is a concern, this is one food where you’ll want to check labels for the ‘organic’ symbol.


SOY: Relationship with Breast Cancer

The evidence is compelling, and the conclusions significant.  Soy will very likely NOT cause breast cancer, and it is safe to consume, and is even a healthy option.  While some early studies in rodents showed questionable effects of soy, we now understand that the phytoestrogen found in soy is NOT human estrogen prevalent in females!  Large studies in human females show that whole soy foods such as miso, tofu and edamame do not increase risk of primary breast cancer or recurrence.

Meanwhile, data suggesting that soy foods may reduce breast cancer risk is exciting and promising!  However, such evidence comes mostly from studies where women had been eating soy foods over a lifetime and therefore had early exposure. We don’t know if starting to eat soy foods later in life confers the same benefits. Women in these studies also may have had other diet or lifestyle habits that contributed to their reduced cancer risk.


The Conclusion

If you have a personal history of breast cancer or are at high risk, go ahead and enjoy the soy, just keep the portions practical.  About 10 grams per day may be best.  Thats a Cup of Soy Milk!  But don’t fret too much.  It’s another good choice when you are looking for a vegetable protein to help round out the diet.


[i] Caan BJ, Natarajan L, Parker B, Gold EB, Thomson C, Newman V, Rock CL, Pu M, Al-Delaimy W, Pierce JP. Soy food consumption and breast cancer prognosis. Cancer Epidemiol Biomarkers Prev. 2011;20:854-58.
[ii] Dong JY, Qin LQ. Soy isoflavones consumption and risk of breast cancer incidence or recurrence: a meta-analysis of prospective studies. Breast Cancer Res Treat. 2011;125:315-23
Cara Anselmo, MS, RDN

Cara Anselmo, MS, RDN, is a nutritionist and certified yoga instructor in New York City.

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