Is Soy Good or Bad For You? The Controversy, Explained

Let’s set soy straight. This legume has quite the rollercoaster reputation—it’s praised as a nutrient powerhouse one day, then scrutinized for potential health risks the next.

So what’s the real story? Should we be adding tofu to our grocery lists or approaching it with caution? Here’s the truth—don’t soy I didn’t warn you (get it?!).  

The Science of Soy

Soy is a nutrient-rich legume packed with protein, fiber, and essential micronutrients like iron, calcium, and folate. But what makes it interesting—and sometimes controversial—is its biochemistry.

Enter: Isoflavones. These plant-based compounds found in soy act as both estrogenic and anti-estrogenic substances in the body. In some tissues, isoflavones weakly mimic estrogen, but in others, they actually block estrogen’s effects.

This dual nature is why soy has generated tons of debate and confusion.

The Misconceptions of Soy

A common myth about soy is that since it can boost estrogen in some tissues, it might increase the risk of breast or other hormonally responsive cancers.

But here’s the thing: A cancer labeled as “estrogen receptor positive” (ER+) does not mean estrogen caused the cancer. It just means the cancer cell maintained its original receptor configuration as it transformed into a cancer cell—after all, all breast cells have receptors for estrogen.

“What about progesterone?” Soy’s impact on progesterone (i.e., the pregnancy hormone) is more up in the air. Some studies suggest soy consumption may decrease progesterone levels, while others show no significant effect.

The reason for this uncertainty is simple: Foods affect people differently. Soy’s impacts can vary dramatically based on whether it’s consumed by women or men, the type of soy, the amount consumed, etc.

Until more research is done, we won’t have a crystal-clear picture of how soy affects women on a broad scale. That said, based on the studies we do have, here are some of its pros and cons:

Pros of Soy  

1. Menopausal Symptom Relief:

Remember soy’s isoflavones? Because they can faintly mimic estrogen, they may alleviate menopause symptoms, such as night sweats and hot flashes.

A 2012 meta-analysis reviewed 19 studies where women took soy isoflavone supplements to see if they help with hot flashes during or after menopause. The researchers found:

• A daily dose of about 54 mg reduced the frequency of hot flashes by 21% compared to a placebo.
• The supplements also reduced how severe the hot flashes were by about 26% (Taku et al., 2012).

A more recent study in 2021 found that a plant-based diet rich in soy, or just a half a cup of soybeans a day, reduced hot flashes by 84%—from nearly five hot flashes per day to fewer than one (Barnard et al., 2021).

2. Bone Health Support:

Those same isoflavones that help with hot flashes may benefit your bones too, though the evidence is mixed. However, a promising meta-analysis found that women taking soy isoflavones showed significantly better spine density compared to those who didn’t (De-Fu et al., 2008).

3. Cardiovascular Benefits:

Soy may help lower the risk of heart disease, especially in younger women and postmenopausal women not using hormone therapy. A study with over 200,000 participants found that eating at least one serving of tofu each week was linked to a reduced risk of heart disease (Le Ma et al., 2020).

4. Cancer Prevention Myths Debunked:

Remember how we debunked those myths about soy and breast cancer? Well, research seems to confirm this. A meta-analysis found that soy consumption was actually associated with a reduced breast cancer risk, especially in Asian populations where soy is a childhood dietary staple (Truck et al., 2006).

Cons of Soy

1. Thyroid Health:

Soy has a…complicated relationship with your thyroid gland. If you have an underactive thyroid (hypothyroidism) or don’t get enough iodine in your diet, eating too much soy could interfere with how well your body absorbs thyroid medication.

The good news is that research shows that eating a moderate amount of soy foods is generally safe, even for those with thyroid issues—as long as you’re getting sufficient iodine (Messina, Nutrients, 2019).

2. Processing Matters:

Not all soy is created equal. Highly processed soy products (e.g., soy protein isolate in snack bars) may not provide the same benefits as whole or fermented soy foods like edamame, tofu, tempeh, and miso.

Don’t Be Soy Afraid

While I was getting my degree in nutrition, the general rule of thumb was you’d have to eat a lot of soy (and I mean a lot) for it to cause any harm.  

In moderation, soy isn’t just safe but also nutritious and potentially beneficial for women’s heart, bone, and hormonal health. Just be sure to choose whole or minimally processed sources of soy rather than highly processed soy isolates.

Here’s to adding edamame and tofu to the grocery list! 🫛

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