Q: I've heard that soy has estrogens in it. Is that good or bad?
A: Soybeans contain compounds known as isoflavones, whose chemical structure is similar to human estrogens; these similarities cause speculation that soy products might have hormonal effects feminizing men or increasing cancer risk in women, for example.
Such concerns have been put to the test. The results show no negative effects from soy on men's hormonal function; soy does not interfere at all with testosterone or sperm production. As for cancer risk, several research teams have tracked the dietary habits of people who've developed cancer and those who've remained cancer-free; compiling the results of these studies in 2008, researchers at the University of Southern California found that women who ate a daily serving of soy products had about a 30 percent reduced risk of developing breast cancer, compared with women who consumed very little soy. (A serving is approximately 1 cup of soymilk, 1/2 cup of tofu, or a similar amount of other soy products.) So a modest amount of soy eaten regularly may actually reduce the risk that breast cancer will occur.
Moderate intake may also boost survival in women who've been treated for breast cancer. The Shanghai Breast Cancer Survival Study followed 5,042 breast cancer survivors for four years. Those who ate two daily servings of soy were about 30 percent less likely to have a cancer recurrence or cancer death, compared with those who avoided soy.
Q: Does soy cause thyroid problems?
A: Not according to the evidence. But if you're hypothyroidmeaning your thyroid gland acts sluggishbe aware that soy products can reduce the absorption of thyroid supplements. If you take these medicines, your health care provider can check if your dose needs to be adjusted.
Q: How can I tell if I am allergic to soy?
A: Like other allergies, a reaction to soy can manifest with hives, flushing, itching, runny nose, or wheezing that occurs shortly after exposure. An allergy can also cause local symptoms, such as swelling of the lips, tongue, or throat, and digestive upset, including abdominal pain and diarrhea. Some people can tolerate modest amounts of soy, and react only when they get too much. In rare cases an allergy can be life-threatening, a condition called anaphylaxis. Most children with soy allergy outgrow it.
But the opposite can occur too. A person can develop an allergy to a food that caused no problem previously. Doctors can easily check for a soy allergy with skin testing and specialized blood tests. But if you think you might be allergic to soy, you can simply avoid it for a few weeks and notice if your symptoms improve. If so, you can challenge yourself with it later on and see if your symptoms return. Do not try this if your allergy symptoms are severe.
Q: Can I be getting too much soy?
A: Not so far as we know, but there's some benefit in favoring minimally processed soy products; edamame and tempeh are tops, followed by soymilk and tofu. Producing meat substitutes often means extracting and concentrating soy protein, so you'??re getting further away from the bean that nature intended.