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One of the most controversial topics in the nutrition field today centers on soy foods. Are they good for us, or bad for us? This isn’t just debated on podcasts and blogs, it is a topic that I have heard discussed at scientific medical meetings with time set aside for experts to debate differing views on this topic. (I’ll tell you the results of that debate shortly.)

In all honesty, I have avoided discussing this topic because there are such strong beliefs on both sides. Over the years though, the fervor against soy has increased – in both the general world and within the world of thyroid health. People have vilified soy, and the growing opinion among the thyroid community has been that it should be avoided, while those concerned about breast cancer and heart disease have been saying that we should be eating more of it.

I think that there is enough evidence on both sides that I need to take a deep breath and share what I know and hopefully it will help you answer this important question, “To eat, or not to eat soy”.

One of the tipping points that encouraged me to write this blog for you now, was a blog written recently by my dear friend and colleague, Alan Christianson, NMD, a naturopath endocrinologist, and a national expert on thyroid health. Alan and I have had discussed the controversy regarding soy food and overall health for years. He shared his evolution on this topic, as the evidence recently has shifted from soy is bad for your thyroid, to soy has a neutral impact on your thyroid, and there are several reasons why you might want to eat soy food.

The Story Against Soy

One of the pieces of evidence initially used to avoid soy food was based on studies of infants raised on soy formula. Initially, these studies showed that infants raised on soy formula had more thyroid problems in life than those raised on a formula developed from cow’s milk (obviously, human breast milk is the best option, but formula is an important option if a woman is unable to nurse her infant). The initial studies used soy milk that was deficient in iodine, iron, and zinc. Once they corrected those deficiencies, the link between soy milk formula and thyroid problems went away. That likely means it was the deficient nutrients in soy formula that was the problem, not the soy milk itself. There is additional weak evidence out of the UK that if you are iodine deficient, have early signs of thyroid disease, and you also consume soy foods, that you might be more likely to develop thyroid problems, but my suggestion would be to avoid being iodine deficient in the first place, and taking a good quality multivitamin would prevent this.

Perhaps the best review of the impact on soy food on thyroid function and overall health is found in an article in the journal Nutrients by Dr. Mark Messina (Nutrients. 2016 Dec; 8(12): 754. Published online 2016 Nov 24. doi:  10.3390/nu8120754). When he combined 14 studies that looked at the impact of soy foods and soy isoflavones on thyroid function, these trials found that none of the soy foods and none of the soy isoflavones (soy hormone extracts) have any effect on thyroid function in either men or women. They looked at TSH, free T3 and free T4 levels, thyroid antibodies, and none were associated with soy food intake.

The only finding that was significant was that if people take thyroid medication (such as levothyroxine), eating soy food when taking the drug would block the medication’s absorption, but this is also true for many other foods, not just soy products. So the bottom line is that people taking thyroid medications should take them on an empty stomach, and they don’t have to avoid eating soy foods.

To sum it up, the case against soy food consumption for thyroid reasons is weak to non-existent.

What about soy food allergies?

Soy is one of the top 7 foods that people react to. If eating soy foods causes you distress, then avoid it. This is similar for gluten and dairy—avoid foods that you are sensitive to. I’ll come back to this point in more detail shortly.

What about GMO soy foods?

I am very concerned about the use of Round-Up and other pesticides that are used on soy products. The producers of Round-Up create GMO (Genetically Modified Organisms)  soy products that can withstand spraying them with Round-Up, making it easy to spray and grow soy crops with Round-Up, as they can kill the weeds without killing the soy plants. However, I consider Round-Up to be a toxic compound that is sadly used on crops across the country, this is a very unfortunate use of GMO technology. The other concern with GMO soy foods is that they can create GMO soy plants that produce their own internal pesticides that kill insects (doesn’t initially sound so bad) but these compounds are neurotoxic to humans as well, meaning they should clearly be avoided.

For this reason, I strongly recommend that if you consume soy foods, you choose organically raised and non-GMO soy products. Although more than 90% of soy products in the USA are likely GMO products, it is fairly easy to avoid them—just select organic, non-GMO soy foods, and don’t buy them if they don’t have an organic, non-GMO label.

WHAT ARE THE BENEFITS OF CONSUMING SOY PRODUCTS? (Please see the article reference mentioned above by Dr. Messina in Nutrients regarding references for all the benefits noted below).

There are multiple strong reasons why you should eat organic, non-GMO soy products regularly:

#1. Eating soy foods helps to prevent breast cancer. And if you have breast cancer, eating soy foods in moderation (1-3 servings per day) will increase your chance of surviving it). This by itself is why I recommend that all women eat organic soy products, and the biggest benefit is for adolescent girls going through puberty. Eating 1-2 servings per day of soy products gives women a lifetime reduced risk for getting breast cancer. That is truly amazing!

#2. Eating soy foods improves menopause symptoms. The evidence again is solid that eating soy foods reduces hot flashes, night sweats, and vaginal dryness.

#3. Eating soy foods improves your cholesterol profile. OK there isn’t a big change in your cholesterol, but eating 1-2 servings per day will modestly improve your lipid profile and achieve some minimal reduction in heart attack risk. Studies have also shown that eating more soy products will decrease arterial plaque growth, as measured by carotid intima-media thickness (carotid IMT) measures.

#4. Eating soy foods decreases the risk for prostate cancer. In the Asian population that eats lots of soy foods, eating more soy foods is associated with a 50% lower risk for getting prostate cancer.

Contrary to reports noted on websites, men who eat soy foods do NOT have a drop in testosterone levels. There were two cases where this did occur, but only when men took massive dosages of isoflavone supplements (soy extracts in huge dosages), nearly 10 times what people would eat from food. Regular soy food intake does not impact testosterone levels or sex hormone binding capacity.

#5. Eating soy foods increases bone density and helps prevent osteoporosis. Studies have shown that consuming more soy products is associated with a lower risk for fractures and better bone density measures.

#6. Eating soy foods “might” improve cognitive function. Initial epidemiological studies following populations over time have shown mixed results as to whether soy products improved or worsened cognitive function. Better designed, more recent studies have suggested that eating soy foods may even improve cognitive function for women who have already reached menopause. However, a couple of other studies with men and women have shown that soy foods had no impact on cognitive function, but at least these investigations noted no harm.

#7. Eating soy foods may reduce inflammation. In contrast to studies claiming that soy causes auto-immune disease and increased inflammation, for the average person, eating more soy food is associated with a decrease in CRP (C-reactive protein) levels, and no worsening in other inflammatory levels.

Of course, if you happen to be soy sensitive, and feel you are intolerant of soy, then I strongly recommend that you avoid soy products. Eating foods that you are sensitive to may increase your risk for auto-immune activity.

I promised at the beginning of this blog to share which expert won the medical meeting debate on eating soy products. After seeing the benefits noted above, I bet you can now appreciate that the person speaking in favor of consuming organic soy products clearly won that debate.


If you tolerate soy products, then I recommend that you can safely eat and will likely benefit from having several servings of soy foods per week, up to 1-2 servings every day. I only recommend organic, non-GMO soy products. You should explore eating edamame, tofu, miso, tempeh, and soy milk and find products you enjoy.

If you feel you are soy intolerant, then clearly avoid soy foods. for at least for 3-6 months, and perhaps long term. Talk to your physician if you should consider reintroducing soy foods in the future (at least after being soy free for a minimum of 3-6 months), and consider food allergy testing with a blood test to clarify if you are in fact soy sensitive.

I have met patients that were initially soy and gluten sensitive. When they completely gave up both for six months and reintroduced soy, and continued to avoid gluten, they no longer reacted to soy protein. I find this a common occurrence. If you are gluten sensitive and you eat soy products, likely your gut leaks food products into your system—this is from eating gluten and initiating an inflammatory reaction, and soy food can literally leak from your gut into your system. You are supposed to have soy food nutrients in your blood, but not soy food. Stop the gluten, stop the leaky gut, and often other food sensitivities, including to soy products will sometimes disappear.

If after giving up gluten, you reintroduce soy products, and your good allergy testing shows that you are soy sensitive (you make antibodies against soy products and have associated symptoms), then yes I recommend that you give up eating soy products long term. My estimate from my 30 years in my clinic is that 10% of people may have a long-term soy food sensitivity, compared to 20% of the population that is gluten sensitive.

If you look at the evidence, It is clear that soy foods have far more benefit than risk. Hopefully, you can discover new ways to enjoy these food products that have been eaten for thousands of years by some of the longest-lived and healthiest populations on the planet.

I wish you the best of health!

Steven Masley, MD, FAHA, FACN, FAAFP, CNS