Are Soy Products Linked to Cancer Prevention?

Katrina Claghorn, RD
Last Modified: November 1, 2001

Dear OncoLink "Ask the Experts,"
I read someplace that a woman trying to avoid breast cancer should have 35-60 grams of soy products per day. I bought some tofu powder (I can't abide the texture of real tofu!) and attempt to mask it in my morning oatmeal.

How many grams of tofu powder is as effective as 35-60 grams of real tofu?  
Thank you.

Katrina Claghorn, RD, Section Editor of OncoLink's "Nutrition During Cancer Treatment" and "Diet and Cancer" menus, responds:

I believe that you are referring to the isoflavones which are in soy foods. The recommended intake is 30-50mg a day. These isoflavones may have many beneficial health benefits. They appear to have a protective effect against breast cancer, decrease symptoms associated with menopause as well as prevent heart disease and osteoporosis.

Isoflavones are sometimes referred to as phytoestrogens or plant estrogens.They have similar properties to human estrogen, but the are much weaker. In addition, they have a chemical shape that is very similar to human estrogen. We believe that the reason phytoestrogens may reduce the incidence of breast cancer is that they fit into the receptor site on breast tissue where estrogen usually attaches. Thus they prevent the more powerful (human) estrogen from attaching and starting the cancer-causing process.

Researchers are still investigating the mechanisms through which soy may protect against breast cancer. The current recommendation is to consume 30 to 50 mg of isoflavones daily to reduce your risk of breast cancer. The best sources of isoflavones are soy milk (30 mg/8 oz), tofu (35 mg/1/2 cup),tempeh (35-mg/1/4 cup), roasted soy nuts (60 mg/1/4 cup) and soy protein powder (approximately 60 mg/2 scoops).

Not all soy foods contain isoflavones. Soy foods made from soy protein concentrate may have little if any isoflavones,so read the ingredient label. Some doctors feel those women with estrogen positive breast cancer or who are on Tamoxifen should limit their intake of isoflavones until we have a better understanding of the effects of phytoestrogens on breast tumors.


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