by Monica Reinagel, M.S.,L.D./N.
Over the past few weeks, I’ve gotten a whole bunch of questions about soy: Is soymilk better for you than cow’s milk? Can eating more soy help prevent osteoporosis, heart disease, or hot flashes? Are the health benefits of soy over-hyped?
Many of you have also written to ask about negative things you’ve heard about soy. Is too much soy bad for you? Are certain soy foods better than others? Should pregnant women or children avoid soy?
There’s a lot to talk about. This week, we’ll take a closer look at the alleged health benefits of soy and see how the evidence stacks up in favor of soy as a health food. Next week, I’ll investigate the charges against soy and whether we have as much to fear as some claim.
Soy Goes Mainstream
Soy has always been popular with vegetarians because it’s an inexpensive source of high-quality vegetarian protein. Lately, though, it’s become much more mainstream. It’s not just a substitute for animal products anymore. Now, it's being promoted as a way to make your diet healthier.
Once upon a time, for example, the only people who drank soy milk were vegetarians or those who were allergic to cow’s milk. Now, half the dairy case at the grocery store is occupied by soy milk, which is being pitched as a sort of nutritional upgrade from regular milk.
Nutritionally, they are fairly similar, but that’s only because soymilk manufacturers work hard to make them that way. Most soymilk contains added Vitamin A, D, and calcium, making it comparable to cow’s milk. Soymilk is free of cholesterol and saturated fat, however, and contains a couple of grams of fiber—which milk does not.
Soy has something else that cow’s milk doesn’t have, and that’s the right to make the following USDA-approved health claim: Diets that include 25 grams of soy protein a day (and are also low in fat and cholesterol) may reduce the risk of heart disease. That’s because eating foods containing soy protein can lower your cholesterol levels. So far, we don’t know why that is.
In order to get 25 grams of soy protein, you’d have to drink about 4 glasses of soymilk. Of course, there are a lot of other ways to get soy protein. You can eat steamed soybeans (otherwise known as edamame), tofu, soy yogurt, soy burgers, or bread made with soy flour.
In general, it’ll take you about four servings of whole soy foods like tofu or edamame to get to 25 grams of protein. With a more concentrated form, like a soy protein powder, it takes a lot less.
The Softer Side of Soy
Now, there are a lot of other health claims for soy that have not yet gotten the official nod from the USDA because research has been inconclusive. Most of these are considered women’s health issues. But, guys, keep listening, because this next part relates to you as well.
It’s been suggested that eating more soy can help prevent osteoporosis, breast cancer, and hot flashes. After all, it has been observed that Asian women, who eat a lot more soy than Western women, don’t seem to suffer from these things nearly as much as we do.
Of course, there are a lot of differences between Asian and Western women that could potentially explain this, such as environment, genetics, lifestyle, or other aspects of diet. These are what we call “confounding factors,” and researchers do their best to account for them when analyzing data. But you can only account for the confounders that you know about—and you never know about them all.
Nonetheless, the soy theory is plausible because soy contains isoflavones, plant compounds that happen to be shaped very similarly to the human hormone estrogen. In fact, they’re close enough that they can actually fit into estrogen receptors in human cells.
Osteoporosis, hot flashes, and breast cancer are all closely linked to estrogen activity in the body—either too much or too little. The thought is that these weak plant estrogens (or, phytoestrogens) might protect you from either scenario. If estrogen levels were low, isoflavones might provide just enough estrogenic activity to prevent bone loss or hot flashes.
On the other hand, if estrogen levels are too high, which might increase your risk of breast cancer, phytoestrogens could help block excess estrogen from entering your cells by occupying the estrogen receptors and causing your cells to turn on the “No Vacancy” sign.
Although it’s an interesting theory, it’s been tough to confirm. Some studies have found that eating soy or taking isoflavone supplements helps improve bone density but some found that it didn’t. Likewise, in terms of hot flashes, soy helps some women but not others. (Incidentally, it seems to be much more effective in reducing hot flashes if you also exercise.)
And as far as breast cancer goes, it’s even more confusing. Some studies show that soy isoflavones seem to protect healthy women from getting breast cancer. But many researchers worry that taking isoflavone supplements (such as those marketed to relieve hot flashes) could promote the growth of estrogen-sensitive cancer cells if you already have cancer.
So, if you have or have had breast cancer, you should definitely check with your health care team before adding any additional soy-based foods or supplements to your diet.
Soy: The Dark Side
Guys, are you still with me? If so, you may be wondering how the phytoestrogens in soy might affect you? Good question! Men have estrogen receptors, too. And, in fact, there are some concerns about how the estrogenic compounds in soy might affect men and small children. And, if that weren’t bad enough, there are rumors floating around the Internet that soy is bad for your thyroid and contains “anti-nutrients.”
I’m going to get into all of these questions in next week’s episode. Here’s a hint to the conclusion of this thrilling cliff-hanger: While eating certain types of soy might be good for you, more is not necessarily better. I’ll be back next week with the details. For those who can’t wait, I’ll post links on the show notes to some of the research I’ve gathered on the topic.
Got a peanut allergy? Soynut butter can be an excellent replacement.
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 nutrition@quickanddirtytips.com. Or find me on Facebook and Twitter. And don’t forget to sign up to receive my weekly newsletter, with more tips, recipes, and answers to your questions.
Have a great day and eat something good for me!
RESOURCES:
Soy: Health Claims for Soy Protein, Questions About Other Components
Soy Plus Exercise Better for Hot Flashes (WebMD)
Soy Isoflavones and Osteoporosis (Journal Article)
Phytoestrogens and Breast Cancer: Promoters or Protectors (Journal article)
Soy: The Pros and Cons (Public Health Services)
