Soy made headlines the past couple years with claims of benefiting heart health, relieving menopausal symptoms, possible prevention of osteoporosis and cancer.
The active substances in soy are protein and isoflavones – a class of phytoestrogens (estrogen like compounds in plants). The Food and Drug Administration has concluded soy protein can lower cholesterol. A diet low in saturated fat and cholesterol, containing at least 25 grams of soy protein daily may help reduce the risk of heart disease.
The evidence of soy’s role in cancer prevention is less clear. The theory is that the isoflavones in soy prevent estrogen (which can encourage the production of cancer cells) from entering breast tissue. Concern has arisen as newer studies show soy supplements actually increasing breast cell proliferation, which increases disease risk.
Researchers are not sure about adding soy to the diet of a woman with breast cancer or at high risk. Dr. Goldin of Tufts University states “two or three ounces of .. . soy based foods wouldn’t be harmful” noting that this is the amount the average Japanese woman eats. But adding soy based foods to your diet in higher amounts is not advised for breast cancer prevention.
Soy powder can also be part of a healthy diet. Be wary, however, of soy powders enhanced with isoflavones, the two most common being genistein and daidzein. Consuming more than 100 milligrams of isoflavones per day – no matter the source – is more than the typical Asian consumer and the effect is unknown.
Soy supplements containing concentrated soy isoflavones are not recommended. Scientists know about soy protein but isoflavones are where the controversy exists. You also risk overdoing it when using concentrated supplements.
The bottom line: soy foods can be part of a healthy diet. As with most things, the food is probably a better choice than the supplement or powder, and all things in moderation. Don’t have more than 3 ounces soy food a day, or more than 100 milligrams isoflavones a day. If you have breast or other hormone dependent cancer, or are at high risk, it may be best to avoid isoflavone supplements altogether. And remember no one food or supplement takes the place of a healthy balanced diet.