Is Soy Healthy To Eat?

I seem to have this conversation a lot, especially with patients and with other health professionals.  We know that incorporating more plant foods and reducing or eliminating meat and dairy is effective for decreasing the risk of heart disease.  One of the best plant sources of protein is soy.  Is soy healthy to eat?

In a recent conversation with a personal trainer, I mentioned that I recommend soy supplements for those looking for weight loss.  You would have thought I was recommending arsenic!  In short order, he rattled off a number of concepts that I had heard before and knew were either myths or highly exaggerated.

Many of my patients use soy for weight loss.  You, Dear Reader, may be one of them 🙂  Just in case your family, friends, or (God forbid) health care professionals tell you soy is dangerous or unhealthy, I want to give you some scientific evidence to use as ammunition.  This of course is not an exhaustive list and new research is coming out all the time, so if you hear about a new study about soy and health, please let me know!

Soy has estrogen and increases breast cancer risk

This one has been pretty definitively disproven.  I reviewed a lot of research about this one recently.  In fact, soy food intake DECREASES breast cancer risk and prolongs survival in women who already have breast cancer.

Soy has estrogen and causes menstrual problems and infertility

Soy isoflavones are plant compounds that bind to estrogen receptors in human cells.  The theory is that since they bind to estrogen receptors they will behave like estrogen in the cells.

Estrogen is a powerful regulator of female fertility and the menstrual cycle.  There is some evidence that a diet high in soy foods can make menstrual periods a little farther apart but there is no evidence that it will interfere with female fertility.  I did find one study that suggested that male sperm count is lower in men who eat a lot of soy, but whether that will interfere with fertility is unclear.

Soy has estrogen and will make men grow “man boobs”

I had to laugh out loud at this one.  I personally have never seen this happen in male patients eating soy foods.  “Man boobs,” or gynecomastia, is growth of the male breast tissue in response to estrogen.  This happens to men who are obese because fat tissue has aromatase, an enzyme that changes a man’s testosterone and other male hormones into estrogens.

I went to the literature and found a study.  Soy doesn’t make men grow breasts.  ‘Nuff said.  If you are a man who is obese and feel you have too much breast tissue, the best option is to work on losing weight.  Soy can help with weight loss and will NOT cause your breast tissue to grow.

Soy has estrogen and will interfere with babies’ growth and development

This has been discussed and debated for years.  Obviously, human breast milk is the best, most perfect food for human infants.  However, if breastfeeding is not possible then soy formula is an option many families choose, especially if the baby seems not to tolerate cow’s-milk formula.

There was a concern that the isoflavones in soy might interfere with babies’ growth and development.  However, studies have shown that babies who are fed soy formula have no difference in growth and development compared to babies who are fed cow’s-milk formula.

Soy causes thyroid problems

This one is interesting.  There actually IS some evidence that the soy isoflavones interfere with production of thyroid hormones, but the evidence is conflicting.  One study showed that people with borderline (called subclinical) hypothyroidism are more likely to progress to clinical hypothyroidism if they eat a lot of soy foods.

There is evidence that eating a LOT of soy (2 grams daily per kilogram of body weight, or 5 ounces for a 150 pound person) can affect thyroid hormone levels very quickly, but the effects do not appear to be permanent.  Eating soy can interfere with the absorption of synthetic thyroid hormone replacement, but so can eating any food too close to taking your thyroid medication.

On the whole, it appears that for healthy people who get enough iodine in their diet (most multivitamins contain the 150 mcg of iodine that people need on a daily basis), eating soy foods does not lead to permanent thyroid problems.

In short, soy is a healthy food that provides plenty of plant-based protein and isoflavones that help reduce blood pressure, heart disease and the risk of breast cancer.  There is no significant danger to the reproductive or hormonal health of people who choose to eat soy.

If you would like to add healthy soy to your diet in an easy, tasty form, please check out Shaklee’s Life Shake.

QUESTION: Do you eat soy?  Why or why not?  (I have soy every single day.  I love it!)


2 thoughts on “Is Soy Healthy To Eat?

  1. Dr. Jen;

    I want you to know how deeply grateful I am that you are an available nearby doctor and practitioner. I’ve been studying integrative nutrition and medicine for over forty years. I’m in a quandary about your stance on soy. Please read my link and help find a happy medium between my research and your declaration.

    Thank you,

    Mary A. Antoniazzi-Greene

    • Hi, Mary Ann! Thank you for the comment. First of all, I disagree with Dr. Mercola about many topics, so I’m not going to address this link specifically. It includes no scientific research citations so these assertions are not backed up with science.

      I personally know many people who have taken cold-processed non-GMO soy protein daily for over 40 years and have nothing but robust health to show for it. I’ve included links in my post to research published in respected peer-reviewed journals. I would like to see primary research that demonstrates documented adverse health effects from soy intake. I’m aware of no research published in the last 5 years that shows that soy is dangerous or unhealthy in any way, with the exception of progression from subclinical to clinical hypothyroidism.

      Hope this helps!

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