Soy What? Navigating Soy Foods For Breast Health

From ice cream to cereals soy is everywhere.
Yet, some soy is better for you than others.
soy products

The explosion of soy containing products on the shelves in the 1990s stems from research discovering those who ate soy protein have lower levels of bad cholesterol (LDL). The popularity of soy has continued as phytoestrogens in soy, called isoflavones, have a similar structure to the female hormone estrogen and therefore mimic the action of estrogen in the body. Studies have found soy isoflavones promote bone, breast and hormonal (menopause, menstration) health.

CAUTION: Consuming soy or soy isoflavones supplements may promote health in premenopausal and menopausal healthy women. However, soy consumption may be harmful for women who have breast cancer, have high risk of developing breast cancer (e.g. family history) or, are suffering from an estrogen-based disease. In such cases, consult your healthcare professional before consuming soy or soy isoflavones as they may increase risk of disease.

Navigating Soy Foods

Packaged soy foods most commonly contain soy protein concentrates, which does not contain the same nutritional make-up as soy foods used in traditional diets and linked to its health benefits. Traditional diets used whole soybeans and fermented soy products. Such foods are thought to offer superior health benefits.

Soybeans can be harvested when the beans are still green and sweet, then boiled and salted to become the popular dish edamame. Whole soybeans are allowed to ripen and then dried. Soy nuts are soybeans that have been dried and roasted. Both forms of beans are rich in protein and isoflavones. When choosing whole soybean foods, seek out organic as to avoid GMO (genetically modified organism) soybeans.

Soy can also be converted into other food items. Textured soy protein (textured vegetable protein) is made from textured soy flour, concentrates and soy fiber. Curdling hot soymilk with coagulant makes tofu. Tempeh is fermented soy with a cake like texture.

Miso and tempeh, as well as soy and tamari sauce, are fermented soy products. When soy is fermented, the microbes break down hard to digest protein and convert isoflavones into more bioavailable forms. In addition, the microbes convert minerals (calcium, iron, magnesium) into more soluble forms, and increase vitamin levels. These elevated nutritional elements of fermented soy make it desirable.

Soy Isoflavones

The main isoflavones in soy are genistein and daidzein. Soy isoflavone supplements offer a concentrated version of these nutrients. Studies have found these isoflavones have multiple ways in which they promote health in the body. Isoflavones prevent free radical formation, as well as increase LDL receptor activity helping to reduce the amount of bad cholesterol circulating in the blood stream. In addition, soy isoflavones increase the production of SHBG (steroid hormone binding globulin) which reduces the amount of estrogen available in the body.

Soy and Breast Health

Isoflavones act like weak estrogens and bind to breast cell receptors effectively blocking the body’s strong estrogens. Studies on premenopausal women have shown daily consumption of 65mg of isoflavones results in an increase in the amount of good estrogen in the blood and bad estrogen excretion through urine. Both of these effects are protective and may reduce the risk of breast cancer.

According to a study reported in the journal Cancer Research, the isoflavone genistein may also slow or reverse the cancer process by deactivating breast cancer genes.

As with most broadly researched areas of nutrition and cancer, there have been studies with varying results. However, a 2014 systematic review on diet and breast cancer published in the International Journal of Food Science and Nutrition states, “The available literature suggests that soy food intake seems to be inversely associated with the disease [breast cancer].” In addition, a multicenter, randomized, double-blind study reported in the American Journal of Clinical Nutrition in 2011 notes the use of soy isoflavones among menopausal women is safe.


Constantinou, A. et al. Induction of differentiation and DNA strand breakage in human HL-60 and K-562 leukemia cells by genistein. Cancer Res 1990 May 1;50 (9s):2618-24.

Mourouti, N. et al. Diet and breast cancer: a systematic review. Int J Food Sci Nutr 2014 Sep 8:1-42.

Soy Isoflavones Monograph, Alternative Medicine Review 1998;3(5).

Steinberg, FM. Et al. Clinical outcomes of a 2-y soy isoflavone supplementation in menopausal women. Am J Clin Nutr 2011 Feb;93(2):356-67.

Xu, X. et al. Soy consumption alters endogenous estrogen metabolism in postmenopausal women. Cancer Epidemiol Biomarkers Prev 2000 Aug;9(8):781-86.