Soy Foods: Perfectly Good Source of Protein Caught in Misinformation

I've noticed something happening in the plant-based section of the grocery store: soy foods seem to be disappearing. You have to look harder to find soy-based yogurts, sour cream and more.

More and more products are made from peas, oats, almonds, cashews and various protein blends. Nothing wrong with those foods, of course. But I can't help wondering whether soy has been quietly pushed aside partly because of one remarkably persistent misunderstanding: Soy contains estrogen.

Except it doesn't.

Soy contains phytoestrogens, naturally occurring plant compounds—primarily isoflavones—that have a chemical resemblance to human estrogen. And that little word phyto, meaning plant, matters.

Phytoestrogens are not human estrogen. They interact with estrogen receptors in the body differently and much more weakly. Depending on the tissue and circumstances, they can have estrogen-like effects or even anti-estrogen effects.

Some of the original alarm about soy and breast cancer came from laboratory and animal studies, including studies using amounts of isoflavones quite unlike what humans normally get from food. Humans metabolize these compounds differently. When researchers actually study people eating soy foods, the frightening story largely disappears.

For women, the fear can be particularly powerful because the word estrogen immediately raises another frightening word: breast cancer.

I 'get it' as I'm a 22-year survivor of Stage III Triple Negative breast cancer.

The reasoning sounds plausible enough. Some breast cancers (HR Positive) are fueled by estrogen. Soy contains phytoestrogens. Therefore, eating soy must increase estrogen activity and perhaps increase the risk of developing breast cancer?

But that conclusion depends on treating estrogen and phytoestrogen as though they were the same thing. Which they aren't.

Soy isoflavones can bind to estrogen receptors, but they are much weaker than the estrogen our bodies produce and can behave differently in different tissues. What matters most is what happens in actual people who eat soy—and human studies have not shown that eating soy foods increases women's risk of developing breast cancer. In fact, a number of observational studies have associated greater soy consumption with a lower risk of breast cancer, particularly among women who have eaten soy regularly for much of their lives, like throughout Asia.

That doesn't mean tofu is a breast-cancer-prevention drug. Populations that eat more soy may differ in many other ways, and an association doesn't prove cause and effect. But it does turn the familiar warning on its head: the evidence certainly doesn't justify avoiding tofu, tempeh, edamame or soy milk because we're afraid their "estrogen" will give us breast cancer.

And apparently women aren't the only ones who've been frightened away from soy.

I've seen another version of the story directed at men: Eat tofu, they're warned, and the phytoestrogens will lower your testosterone, enlarge your breasts or otherwise make you less "manly." It's another case of that troublesome word estrogen doing more work than the science supports.

Clinical research has specifically looked at this question. A meta-analysis of 41 studies found that soy protein and soy isoflavones did not significantly affect men's testosterone or estrogen levels. There have been a few case reports involving extraordinarily high soy or isoflavone consumption, and those stories have traveled widely on the internet - because that's something the internet is really good at ... amplifying misinformation. But unusual individual cases aren't evidence that eating ordinary amounts of tofu, tempeh or edamame causes men to grow breasts.

Men certainly can develop enlarged breast tissue—a condition called gynecomastia—but it has a number of recognized causes, including hormonal changes, certain medications and some medical conditions. Ordinary soy consumption isn't established as one of them.

So perhaps the simplest lesson applies to both women and men:

Phytoestrogen isn't estrogen. Soybeans aren't hormone pills. And we shouldn't let a misleading similarity between two words frighten us away from a nutritious food.

Soybeans are legumes. They're an excellent source of protein and also provide fiber, healthy fats and important nutrients. Tofu, tempeh, edamame and unsweetened soy milk can be wonderful components of a healthy plant-based diet.

One important distinction: soy foods are not the same thing as concentrated isoflavone supplements. Supplements can deliver much higher doses, and the evidence concerning them is less certain. Eating tofu for dinner is not equivalent to swallowing a bottle's worth of isolated phytoestrogens.

And, speaking of dinner, there’s another irony in our complicated relationship with soy. While some of us carefully avoid tofu or soy milk because we’ve heard vague warnings about phytoestrogens, enormous quantities of soy are being fed to the animals we eat. Chickens, pigs, dairy cows and farmed fish commonly consume soy-based feed—and few of us give that a second thought when we eat the resulting meat, eggs or dairy products. Of course, eating an animal that ate soy isn’t the same as eating soy ourselves; the animal has digested and metabolized it. But from an environmental standpoint, there’s an even stranger twist: instead of eating this nutritious, protein-rich bean directly, we grow vast quantities of it to feed animals, losing considerable food energy and protein along the way. Perhaps soy isn’t the food we should be worrying about. Perhaps we should be wondering why we’ve become so suspicious of eating the bean ourselves.

So perhaps it's time to stop being frightened by a word and a bean.

Estrogen and phytoestrogen are not interchangeable. And soybeans are not estrogen pills. I'd hate to see an extraordinarily useful, nutritious and ancient food pushed off our plates because we confused the two.

NOTE: If you're a breast cancer patient, survivor or have a family history of the disease, and want to read more about soy and breast cancer, I refer you to the following article from the University of Texas, M.D. Anderson Cancer Center (where I received all my treatment) : https://www.mdanderson.org/cancerwise/is-soy-safe-for-patients-with-breast-cancer.h00-159538167.html