Protective Foods - How Soy Isoflavones Help Protect Against Cancer

When it was discovered that the breast cancer risk of Asian women is much lower compared to Asian-American women, scientists began to search for an explanation.¹ (Most Asian countries have lower incidences of uterine, prostate, and colon cancers, as well.²) Much of the research on this phenomenon has centered on the fact that people in Asian countries eat more soy products that people in Western countries. Researchers believe that certain chemicals in soybeans called isoflavones are responsible for the lowered risk.³

Isoflavones are phytoestrogens (phyto means "plant"), which act like the estrogen police when inside your body. They keep estrogen levels under control as they can act both like a weak estrogen when body estrogen levels are low and can inhibit estrogen's effects when body estrogen levels are high.⁴ Isoflavones can attach to the same spot on cells that estrogen found in the body would. If there is too much estrogen in the body, like in premenopausal women, isoflavones block it from affecting cells. If there is not enough estrogen, like in postmenopausal women, they mimic it and produce similar, but milder, effects.³

The two main isoflavones found in soybeans and soy products are genistein and daidzein.³ In many studies, genistein has been shown to inhibit the growth of cancer cells, especially those of the breast, prostate, colon, and skin.³ Daidzein has shown similar anticancer effects.³ Encourage your young daughters, granddaughters, and nieces to eat soy products, as isoflavones may have the most influence on preventing breast cancer early in life.^1,3

Soybeans are superheroes whose résumés stand out among the rest. Along with fighting cancer, they are also thought to aid in lowering the risk of cardiovascular disease, reducing cholesterol, preventing osteoporosis, and lessening menopausal symptoms.^2,4

Food Sources

Isoflavones are found in soybeans and soy products, such as tofu and tempeh. Tofu, also known as bean curd, is made from curdled soymilk and comes in three different textures—firm, soft, and silken. It is extremely versatile in that it readily soaks up the flavor of the foods or sauces with which it is cooked. Tempeh is a fermented soybean cake with a smoky or nutty taste.² Both of these foods, along with textured soy protein, can be prepared in the same ways as meat. Table 1 shows the isoflavone content of several different products. It is easy to add more isoflavones to your diet because there are so many ways to incorporate soy products into what you would normally eat.

Tips for Increasing Isoflavones in Your Diet

• Instead of peanuts, snack on roasted soybeans (also known as soynuts).
• Try soymilk on your breakfast cereal instead of cow's milk.
• Replace up to one-quarter of the regular flour in baked goods with soy flour.
• Use textured soy protein in place of meat in your favorite recipes.
• Make cancer-fighting stir-fries, soups, casseroles, shakes, and pies with tofu.
• Fire up the grill and enjoy barbequed tempeh.
• Top your salad with miso dressing.
• Sip on a tasty smoothie or shake made with soymilk.

References
1. Lamartiniere CA. Protection against breast cancer with genistein: a component of soy. Am J Clin Nutr 2000;71(suppl):1705S-7S.
2. Anderson JA, Smith BM, Washnock CS. Cardiovascular and renal benefits of dry bean and soybean intake. Am J Clin Nutr 1999;70(suppl):464S-74S
3. Messina MJ. Legumes and soybeans: overview of their nutritional profiles and health effects. Am J Clin Nutr 1999;70(suppl):439S-50S.
4. Wiseman H, O'Reilly JD, Adlercreutz H, et al. Isoflavone phytoestrogens consumed in soy decrease F2-isoprostane concentrations and increase resistance of low-density lipoprotein to oxidation in humans. Am J Clin Nutr 2000;72:395-400.

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