Soy: is it bad for you?

Half the time, when I talk with people about eating a plant-based diet, I hear that I should avoid soy. It seems that most of the people around me worry that soy is full of estrogen. Ironically, most of these people regularly consume dairy products. When pressed on the subject, my friends usually think it would be ideal to avoid both. A week later, they are still only avoiding soy. Why? Is soy really bad for you or is this more propaganda against giving up meat?

Many people switch from meat to tofu and quickly benefit from reduced saturated fat and cholesterol. Sure, you can still get these benefits from a plant-based diet without consuming soy.

Most people, who accept the logic of a plant-based diet, would agree that tofu is safer to eat than steak. Those same people would also agree that tofu or edamame is better for you than a tofu dog or other processed soy products because many of the nutrients in soy, like fiber, are filtered out in the process of making the tofu dog or tofu-based cream "cheese."

People worry about consuming the estrogen in soy because for years we were told that estrogen caused breast cancer. Many blogs still support this idea. Is it true? Does soy even contain estrogen?

When I started writing this post, I knew that soy contained isoflavones and phytoestrogens. I've been reading up on what that means:

Isoflavones are polyphenolic compounds that possess both estrogen-agonist and estrogen-antagonist properties. For this reason, they are classified as phytoestrogens — plant-derived compounds with estrogenic activity. Isoflavones are the major flavonoids found in legumes, particularly soybeans.

We know that during the early stages of breast cancer estrogen encourages cancer cells to grow and spread. This makes many doctors worry that soy could make things worse for women with breast cancer. A 2014 American study looked like it may support this idea, but the study lost funding and couldn't go on long enough for conclusive results. During this study, 70 women at the early stages of breast cancer consumed four cups of soy milk a day, while 70 others consumed a placebo. I don't know anyone who consumes that much soy per day. They found that several genes that encourage cancer growth were active in women in the soy group. They didn't find out if this actually caused cancer to grow.

They also didn't find out anything about the effect of soy on people who don't have cancer. Many studies suggest that consuming soy prevents cancer, including prostate cancer in men.

In fact, soy has been found to have so many health benefits that it is available as a supplement. People take soy supplements to treat high blood pressure, heart diseases, type 2 diabetes, asthma, lung cancer, endometrial cancer, prostate cancer, thyroid cancer, osteoporosis, and kidney disease. It's used to regulate bowel movements, improve memory, to relieve muscle and breast pain, for menopause, and premenstrual syndrome. People also take it to prevent breast cancer. Though, we all know how I feel about supplements.

A study of the quality of commercially available soy supplements suggests that less than 25% of products contain within 90% of labeled isoflavone content. Paying more for a product doesn’t necessarily guarantee that the content shown on the label is accurate. 

But wait a minute... can soy prevent cancer?

When we want to know more about the benefits of plant-based diets, we keep looking to China because the Chinese have been eating plant-based diets for centuries. Researchers studied more than 73,000 Chinese women and found that those who ate at least one or two servings of soy per day were 11% less likely to develop breast cancer than those who did not.

Of course, there are problems with that study too, at least when we apply it to the lives of women who ate McDonald's and Dairy Queen as kids, rather than tofu and miso. We don't know how soy benefited those women in China. Did it start to work when they were children? Is starting a soy diet at 40 too late?

I don't know. None of the research available is persuasive enough for this skeptical woman. I would likely be more concerned about soy if I had breast cancer. If I had breast cancer, I wouldn't take advice from my blog, but would listen to the professionals helping me get rid of the cancer.

If you don't have cancer, these studies are only telling you to eat soy in moderation, by which they mean one or two servings per day. That doesn't sound very moderate to me, but I'm less concerned about soy now than I was when I started researching it.

Thanks for reading. Please share any more information about the benefits and dangers of soy in the comments.

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