by Monica Reinagel, M.S.,L.D./N.
On last week’s show, I started talking about the pros and cons of eating soy. If you haven’t listened to that show yet, you might want to go back and listen to it now because we’re going to pick up where I left off.
In last week’s show, I talked about some of the health benefits of eating more soy. It’s promoted as a way to prevent heart disease, osteoporosis, breast cancer, and hot flashes.
But as soy’s healthy reputation has grown, there has also been an ever-louder chorus of nay-sayers who claim that soy is actually quite unhealthy. This week, I want to take a closer look at some of these charges. At the end of the episode, I’ll give you some recommendations about including soy in your diet.
As I explained last week, soy contains compounds called isoflavones, which are very similar to the hormone estrogen. In fact, isoflavones are also called phytoestrogens, which means “plant-estrogens.”
We’re still not entirely sure how phytoestrogens work in the human body but we think that they are beneficial. They can help compensate for low estrogen levels and, at the same time, help block the effects of excessive estrogen. In theory, this could help prevent a whole bunch of health problems, including hot flashes, osteoporosis, and breast cancer.
However, some fear that eating too much soy could potentially have harmful effects on men. Too much estrogen could theoretically affect fertility or sexual function.
In fact, scientists have found that giving large amounts of phytoestrogens to animals can indeed affect fertility. Keep in mind, however, that men have been eating soy and plenty of it for centuries in Asia and have not experienced population-wide fertility issues.
Could Phytoestrogens Harm Babies?
There are similar concerns about eating soy during pregnancy and giving soy formula to babies. The idea is that babies, both in the womb and out, are extremely sensitive to hormones and that phytoestrogens might affect their development. Again, I’ll point out that Asian women have eaten soy throughout their pregnancies and while nursing for centuries without apparent difficulty.
Soy baby formula is a newer development, however, and there is some reason for concern here. I think we can all agree that human breast milk is by far the optimal food for babies. Sometimes, however, breast-feeding is not an option. Soy formula can be a lifesaver for babies who have an allergy to cow’s milk. But, while there is no hard and fast evidence that soy formula causes problems, many pediatricians agree that it’s best not to give soy formula to babies unless you absolutely have to—just in case.
Other Charges Against Soy
Another widely-repeated charge against soy is that it disrupts thyroid function. In fact, studies overwhelmingly show that it has minimal, if any, effect on thyroid function in human beings, except if they are deficient in iodine. Iodine deficiency is rare, thanks to our iodized salt supply, so I don’t think this is a major concern.
If you’ve read any of the anti-soy manifestos on-line, you’ve probably also read that soy contains “anti-nutrients,” which sound very sinister indeed. In fact, there are compounds in soybeans called phytates which can impair your ability to absorb certain nutrients. This is not unique to soy, however. Spinach contains compounds called oxalates, which do the same thing, and people don’t go around talking as if spinach were a vegetable from the dark side. Really, this is not a big deal if you’re eating soy in reasonable quantities as part of a nutritious diet.
Fermenting soy removes or deactivates many of the so-called anti-nutrients. Fermented soy foods include miso, tempeh, natto, and soy sauce. Many consider these to be the ideal way to consume soy.
Another charge against soy is that it may be genetically modified. It’s true that most of the soy grown today is genetically modified to withstand common pesticides and herbicides. If it’s important to you to avoid genetically-modified crops, look for soy products that are certified GMO-free.
So, Should You Eat Soy or Not?
By this point you’re probably wondering if the possible health benefits of soy are worth the risks—even if the risks are unproven or exaggerated. Ultimately, that’s a decision you’ll have to make. But, for what it’s worth, here’s my take on the controversy.
There are a few groups of people who might want to avoid soy, out of an abundance of caution. If you have or have had breast cancer or have poorly controlled thyroid disease, you might want to steer clear. I’d also use soy baby formula only as a last resort.
Soy is also a fairly common allergen. My fellow pod-caster Grammar Girl reports that she got very ill after she went on a “big soy kick” a few years ago and finally realized she was highly allergic to soy.
Other than these situations, it’s very unlikely that healthy adults will experience negative effects from eating whole soy foods in moderation. In other words, while some soy might be good for you, more is not necessarily better. And, as with most foods, the less processed, the better.
If the potential benefits of soy appeal to you, incorporate whole or fermented soy foods like edamame, tofu, soymilk, miso, and tempeh into your diet on a regular basis. But there’s no need to go overboard. Two or three servings a day is plenty!
I think more research is needed before we can say for sure whether soy isoflavone supplements are helpful and not harmful. And there’s plenty of research underway. I’m going to post a bunch of links on the show notes if you’d like to see some of the studies that I reviewed. In the meantime, though, I’ll take a pass on soy protein powders and isoflavone supplements.
Although you’d never guess it from the titles of his books and articles, the most strident soy-basher on the Internet (and you know who you are) arrives at pretty much the same prescription.
This is Monica Reinagel, the Nutrition Diva, with your quick and dirty tips for eating well and feeling fabulous.
These tips are provided for your information and entertainment and are not intended as medical advice. Because everyone is different, please work with your health professional to determine what’s right for you.
If you have a nutrition question for me, send an email to firstname.lastname@example.org or leave me a voice mail at 206-203-1438. As always, you can also find me on Facebook or Twitter.
By the way, I recently did an interview with Ben Greenfield, of the Ben Greenfield Fitness podcast. The topic is childhood obesity and what we adults can do to help raise the next healthy generation. You can find that interview on itunes or at BenGreenfieldFitness.com.
Have a great day and eat something good for me!
Soy: Health Claims for Soy Protein, Questions About Other Components (USDA)
Phytoestrogens and Breast Cancer: Promoters or Protectors (Journal article)
Soy: The Pros and Cons (Public Health Services)
Safety of Soy Based Infant Formulas (Journal Article)
Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. (Journal Article)
Soy: Healthy or Harmful? (Joe Mercola, ardent soy detractor)