Should you avoid soy — or not?

If you’ve heard me say this one thing loud and clear, you’ve heard me say it a million times: Eat real food, not too much, mostly plants.

While that statement answers about 99 percent of diet-related questions, it does leave one question unanswered: Should you eat soy?

Patients and readers often ask me about the risks of soy: Is there a connection to cancer? Can it help hot flashes? And as a cardiologist, I’m probably asked most often…

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Is soy really beneficial for heart health?

Researchers had previously suspected that soy is beneficial for heart health, but they couldn’t be too definitive since people who eat things like tofu are also more likely to eat fruits and vegetables and exercise, making it difficult to narrow down the exact cause of the benefits.

But recently, the evidence really swung in soy’s favor…

When scientists looked at data from three big studies that included over 200,000 people, they found that people who ate tofu more than once a week were less at risk — 18 percent less, in fact — of a heart event. When you get to really large numbers of people in any analysis, it’s much more likely that the effect is real.

Heart disease prevention? Check.

But what about soy and breast cancer?

But what if you’ve been told to avoid products with soy because you have estrogen-receptor positive breast cancer? Rest assured that Step One Foods don’t have any estrogenic properties. Our Dark Chocolate Crunch and Dark Chocolate Peanut Butter bars, the only soy containing products in our collection, contain only the lecithin component, which has no phytoestrogenic properties or isoflavone components.

But in a broader context, avoiding all soy may actually not even be necessary if you have or are at risk for breast cancer. The phytoestrogens in soy, also known as isoflavones, are just different enough structurally that they don’t appear to exert the same effects as human or medicinal estrogen. In fact, according to Harvard’s Dana-Farber Cancer Institute:

  • Phytoestrogens are structurally different and significantly weaker than human estrogen.
  • Phytoestrogens do not turn into estrogen when you eat them.
  • Moderate intake of soy, in food form, does not increase cancer growth.

People hear the word “estrogen” in the word “phytoestrogens” and assume that means soy has estrogen-like effects. Not necessarily — and it’s far more complicated: We have estrogen receptors in various tissues in our bodies and not all estrogen effects are bad. For example, even though high levels of estrogen can increase the likelihood of developing breast cancer, those same levels of estrogen can be good for bone density.

Ideally, what you want is a “selective estrogen receptor modulator” that would have pro-estrogenic effects in tissues you want affected by estrogen — like bones — and anti-estrogenic effects where you’d like to minimize effects — like breast tissue. Well, that’s what soy phytoestrogens appear to be — selective modulators. Cultures that eat a lot of soy experience significantly lower breast cancer rates — an anti-estrogenic effect. Meanwhile, tofu consumption can significantly improve hot flashes — a pro-estrogenic effect.

So with soy, we seem to get all the benefits without the risk. Yet another high-five for food and another reminder about how complex our bodies are…

According to Dana-Farber again: “Research in patients with breast cancer patients suggests possible benefit to overall survival with consuming moderate amounts of soy foods, or 1-2 servings per day. One serving of soy is equivalent to ½ cup of edamame, 1 cup of soy milk or ¼ cup of tofu.

The bottom line is that soy foods like edamame, tofu and unsweetened soy milk can safely be included as an alternative protein or dairy source, even for those going through cancer treatment.”

Soy or tofu?

But just like you should be consuming foods closer to their original form in general, this is also true for soybeans. The data is not supportive of using soy protein supplements or soy derivative products like meat alternatives, soybean oil or soy fortified foods for preventing cancer or for improving cancer survival rates.

So, stick with the original or close to it. Low in fat but high in fiber, iron, magnesium, potassium, protein and zinc, edamame is one of my favorite beans. I order a bowl every time we go out for sushi — although I ask that the preparer go easy on the salt. And I add edamame beans to salads when I’m at home. And even though I don’t cook with it, I often order tofu-based stir-fries or stews when eating out.

But I most definitely stop at tofurky!

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Dr. Elizabeth Klodas MD, FACC

By Dr. Elizabeth Klodas MD, FACC

"Diet is a major driver of high cholesterol, but instead of changing the food, we prescribe medications. This never seemed logical to me.” Dr. Klodas has dedicated her career to preventive cardiology. Trained at Mayo Clinic and Johns Hopkins, she is the founder and Chief Medical Officer for Step One Foods. Dr. Klodas is a nationally sought out speaker and has an active role at the American College of Cardiology. Her clinical interests include prevention of heart disease and non-invasive cardiac imaging and she has published dozens of scientific articles throughout her career. Dr. Klodas has been featured on CNN Health for her mission to change how heart disease is treated. An independent study performed at leading medical institutions affirmed the ability of Step One Foods to deliver measurable and meaningful cholesterol-reduction benefits in the real world. The results of the trial were presented at the 2018 American Heart Association’s Scientific Sessions. Dr. Klodas has also authored a book for patients, "Slay the Giant: The Power of Prevention in Defeating Heart Disease," and served as founding Editor-in-Chief of the patient education effort of the American College of Cardiology. In addition to her practice and her duties at Step One Foods, she also serves as medical editor for webMD.