April 19, 2014
How much have you heard about health benefits or risks of eating soy foods? Maybe your doctor has advised you to include soy foods in your diet for heart health or to eliminate them to reduce breast cancer risk. Or maybe even include them to reduce breast cancer risk. So wait, is it healthy or harmful? I was pretty confused about soy foods myself before I became a dietitian (and for a time after!), so hopefully I can help you clear up the confusion.
Soy is a plant-based source of protein and it’s a complete protein at that (which means it contains all the essential amino acids needed by our bodies in the correct proportions). In addition to protein, soy provides fiber, potassium, essential fatty acids, folate, other vitamins and minerals, and isoflavones. It’s the isoflavones that seem to cause many soy-skeptics the most concern.
Soy Foods and Breast Cancer Risk
Isoflavones are phytoestrogens, which are chemically similar to estrogen. Two major types of isoflavones, genistein and daidzein, can act like estrogen in the body, but at a much lower level of potency than free circulating estrogen in women. So if these isoflavones act like estrogen, you would imagine that soy could increase your risk of estrogen-receptor (ER) positive breast cancer (this is one type of breast cancer which is spurred on by the binding of estrogen to breast receptors for the hormone). In some studies with laboratory animals, rats injected with ER-positive tumor cells that were given the highest amounts of isoflavones had the greatest growth of tumor cells. BUT, that isn’t the case in all animal studies.
When analyzing epidemiological studies in which women were asked about their normal diets and followed over many years, researchers have found either no association between soy food consumption and breast cancer, or a protective association (women who reported eating more soy foods had lower rates of breast cancer). Keep in mind these studies focused on whole soy foods in the diet, not soy supplements. More research is needed to understand the benefits or risks of isolated soy compounds like those found in soy protein supplements or foods with high amounts of soy protein isolate (like some nutrition bars).
What about women who are ER-positive breast cancer survivors? Various research studies have found no harmful effects to eating soy foods for breast cancer survivors. How can isoflavones, which mimic estrogen, NOT have a negative effect on women who have a history of ER-positive cancer? Researchers aren’t sure of the exact mechanisms, but isoflavones also have anti-estrogen properties, which means they can block stronger natural estrogens from binding to the breast receptors.
Soy Foods and Heart Health
Soy and heart health is one of the most researched of all soy/health links. Studies show that soy foods can help reduce total and LDL-cholesterol and triglycerides. The link is so strong that the FDA authorized the following food-labeling health claim: “25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. A serving of (name of food) provides ____ grams of soy protein.”
The Bottom Line:
To reap the health benefits of soy without the (possible) risk, enjoy soy foods and pass on soy supplements or isolated soy compounds.
Easy Soy Food Additions
- Add edamame or tofu to your next stir fry or fried rice
- Make your next smoothie with soy milk or silken tofu
- Try edamame hummus—make your own or try Eat Well Enjoy Life
- Munch on soy nuts or dried edamame for a snack
- Swap soy crumbles for some or all ground beef in pasta sauce or chili