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.
SO WHAT IS THE BOTTOM LINE WHEN IT COMES TO EATING SOY?
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
What about soy oil? Can I eat mayo that is 90% soy?
I prefer other oils with less inflammatory omega-6 fats. Avocado oil, almond oil, and extra virgin olive oil are better choices.
Steven Masley, MD
Hi Dr. Massey,
I had DCIS stage zero in one breast in 2010. I had the “abnormal tissue” removed to safe margins around the small area. I was then on Tamoxifen for 6 years. I stopped taking it, as it was making me feel sick. I have since learned that it can be toxic to the body, so I am glad I stopped taking it. I have not had any issues since 2010, thankfully!
I was told not to eat soy foods, because DCIS is an estrogen based cancer, and that soy helps in the production of estrogen. I am not a big soy eater to begin with, but I do like the soy milk, and will eat tofu occasionally. What is your opinion on eating soy with my past diagnosis?
I am delighted that you have passed the 8 year mark. Congrats!
Share this link with your doctor. There are several studies in the US and in China showing that for women who have had breast cancer, eating soy products decreases their risk of dying from breast cancer. Every person is different, so check with your own physician.
Steven Masley, md
I really appreciate this information. It helps to clarify for us the many variables that go into “yes or no” thinking about any foods.
I am surprised by this article. Haven’t I heard for years that soy is a culprit in causing breast cancer? Avoid avoid avoid. Now it helps to heal and prevent? I’m very confused about this
You are correct that this has been a confusing discussion for years. Soy products act a bit like Tamoxifen the drug used to prevent and treat breast cancer. For more than a decade, the evidence has been very solid that eating soy products decreases your risk for getting breast cancer. One of the controversies was should you eat it if you have breast cancer. The best study published in the prestigious medical journal, JAMA, showed that for women with breast cancer, eating soy products decreases their risk for dying from breast cancer.
THE BOTTOM LINE–Eating 1-2 servings of soy products daily decrease your risk for getting breast cancer, and if you have it, from dying from it. However, I still only recommend organic, non-GMO soy, and if you are soy sensitive (perhaps 10-15% of people), best to avoid it.
I hope this helps you understand the critical point.
Steven Masley, md
Tammy – what it boils down to is that less than 1% of the soy in the supermarkets is safe to eat. Only non GMO soy is safe and fermented is best. Otherwise AVOID soy like the plague!
It is pretty easy to find organic, non-GMO tofu, soy milk, edamame, miso, and many other soy products in large chain grocery stores. In most health food stores, the majority of soy products are organic and non-GMO.
99% percent of soy products are GMO, but most of them are fed to cattle, pigs, farm raised fish, and chickens. So if you want to avoid GMO soy products, be sure to buy organically raised meat, poultry, eggs, and fish. As the chemicals eaten by the animals are in the animal fat.
Steven Masley, MD
Hi, Dr. Masley ~ What about the research done by the Weston A Price Foundation which discovered 14 separate populations throughout the world (representing all races), all of whom are among the healthiest and longest-living people on the planet today? None of them consume soy products with the exception of an Asian population who consumes only fermented soy; i.e., miso and tamari. They do consume, among other things like fruits and vegetables, high-quality animal fat products. This was common amongst these 14 populations. Are you familiar with the work of Weston A Price?
Thank you ~ Milanne
The Asian groups eat tofu and edamame often, up to 1-3 servings per day depending upon what source you follow. They don’t just eat fermented soy products, although they do consume miso frequently.
Of the blue zones, the longest lived on the planet are from Okinawa, where soy products (fermented and non-fermented) are commonly consumed.
The theme that all the blue zones have in common is eating lots of fruits and vegetables, smart fats, they are highly active, they avoid toxins, and they have social support and are connected in their communities. Eating high-quality animal fat products is not a common theme, as some are vegetarian, although some of these groups do eat wild and pasture raised animal products.
Steven Masley, MD, FAHA, FACN, FAAFP, CNS
Thank you so much for this . There is so much demonizing and misinformation out there about soy. I find plenty of organic, non-GMO tofu, tempeh, etc, in supermarkets and asian markets just fine. All the non-GMO soy is fed to livestock or used in processed garbage.
Hi Dr Masley, very good article. I am concerned with soy Isolate, which I was told that petroleum is used during the process. Many people objected to this process, not sure if they are still using it. If so, it doesn’t sound good.
That is a good point. I do not recommend that people use soy isolates (extracts), only non-GMO, organic soy products, and limit themselves to 1-2 servings per day.
Steven Masley, MD
It is my understanding that people with thyroid disease should not eat soy because it can interfere with meds. . Same with cruciferous veggies. I asked my endo why not the cruciferous veggies and he said it was because of the iron. Also, that they can interfere with thyroid meds. After years of taking Synthroid I switched to a natural thyroid and have done much better. I quit using soy after reading about it affecting meds. But, like you, I also became concerned about the Roundup being used, thanks to Monsanto. I only eat organic, but you even have to be careful of organic these days, unless you grow it yourself or get from a local farmer.
Please send the article referenced by Dr Messina to your endocrinologist. Hopefully she/he will appreciate the update.
Cruciferous veggies are a problem only if you juice them and consume super high dosages. They do not have excessive iron. All foods can block a small amount of thyroid medication absorption, not just soy foods. That is why thyroid medication manufacturers suggest you take your medication on an empty stomach. i am glad that you switched from Synthroid (only synthetic T4) to natural thyroid (likely Armour or Naturethroid) as both contain T4, T3, and T2–which is much better therapy.
Steven Masley, MD
Where do you buy your natural thyroid meds, I would love to drop the synthroid
You would need to get a prescription from your doctor. With my patients, I recommend either Nature-throid (which is temporarily hard to find and some dosages are out of production) and Armour thyroid medication. Natural thyroid medication provides a mixture of several thyroid forms (T2, T3, and T4), while Synthroid (levothyroxin) is only T4. As your thyroid receptor sites are largely T2 and T3, and only some T4, your body may not convert enough to the T4 form, and 20% of people taking only T4 may have low thyroid symptoms, despite that their levels of T4 and TSH appear ok, related to not making this conversion properly.
FYI, some conventional physicians refuse to write for natural thyroid medication. Most functional medicine physicians prefer natural thyroid medications.
Steven Masley, MD
In Asian countries they only eat fermented soy.
There is oxalic acid (spelling) that is not good for you in raw or cooked soy.
My friend, a vegetarian, attributes his memory loss to eating a lot of soy. He now eats only fermented soy if he eats it at all.
Look into the difference between raw/cooked soy and fermented soy.
I do not eat soy products and find it difficult to find products without soy in them.
Soy sauce is fermented.
Sorry, but in Asian countries, they eat plenty of tofu and edamame, and they drink soy milk, which are all non fermented soy products, and specific areas in Asia with the highest intake have the longest healthy lifespans on the planet, like Okinawa. I have lived and worked in several countries in Asia, and reviewed consumption rates recently.
Yet historically, they only consumed natural soy foods. They didn’t have the GMO produced soy that is common today. And to repeat myself, if you eat soy food, I only recommend organically-raised, non-GMO soy. The biggest source of GMO soy in the western diet is animal protein, as in they feed the GMO soy products to cows, pigs, chickens, and fish, and if you eat these foods, you also consume the chemicals that were applied to the GMO soy plants.
Fermented soy foods are easier to digest, here we agree, and for this reason, some people only choose fermented soy foods, which for some people is a good choice. But the health benefits from soy foods in published studies come from either fermented or non fermented soy foods, the preponderance of scientific evidence shows that both are beneficial.
One of the reasons that I hesitated to write this blog on soy, was because of the all the myths that are commonly believed regarding it. But if you actually limit your reading to scientific articles, it is easy to come to the conclusion that soy foods are more beneficial than negative.
However, if you are soy intolerant, (as in when you eat soy, if you get GI symptoms, a rash, or joint achiness) then I agree that you should avoid eating soy products. Soy products, just like eggs, dairy, wheat, corn, shrimp, strawberries, and peanuts can cause food intolerances. But not everyone is intolerant to all these foods, so everyone doesn’t need to avoid all of them.
However, there is no scientific credible data that soy products cause memory loss, and there is decent but not conclusive data that eating modest soy intake prevents memory loss (although eating GMO soy products can cause multiple health problems.) Nor does eating soy cause thyroid disease (another myth–please read the references noted in my blog) and eating 1-2 servings of soy products daily decreases your risk for breast cancer, prostate cancer, bone loss (osteoporosis), and improves menopause symptoms. I hope you would agree that these are pretty amazing benefits.
Whether you avoid soy, or eat it, I want to ensure you have the best information possible, so that you can make the best decision for your own health.
I wish you the best of health!
Steven Masley, MD
Dr Masley I guess you have avoided the much studied topic that soy increases estrogen in men! There has been many studies in this are as well as books that instruct men to avoid this food. I test my hormones yearly and the last test was high in estrogen and was advised by my doctor to avoid soy and take supplements to reduce it.
James, What you are saying is a common myth and simply not true. If you have published clinical research articles, I am always happy to read articles from established medical journals, so please share them. But please don’t send links from websites with people who are only sharing opinions.
The reality is that soy foods block estrogen activity at the estrogen receptor site (they have agonist/antagonist activity). That is why we recommend that women who have estrogen positive breast cancer should consume modest amounts of soy foods, so block their estrogen receptors. So in men, eating 1-2 servings of soy products daily would actually decrease your overall estrogen activity. I am sorry that your doctor didn’t clarify this for you.
Men form estrogen largely from testosterone. Their fat cells convert testosterone into estrogen. Some of my male patients have elevated estrogen levels, not because they eat soy foods, but because they are overweight and their fat cells convert their testosterone into estrogen. Other sources of estrogens in men’s diets come from plastics and other chemicals in our environment–many of the toxins in are diet have estrogen like activity.
Eating 1-2 servings of soy foods daily will NOT increase your estrogen levels, and will decrease your overall estrogen receptor activity. However, high dosages of soy isolates consumed as soy isoflavone supplements can impact estrogen activity, but this would be 10-30 times the dosage that comes from soy food.
Several studies have shown that eating soy foods does not impact men’s testosterone levels, and it does not cause men to grow man boobs either. Being over weight is the primary cause for man boobs, although a few men have a genetic tendency to forming breast tissue even when they have normal weight.
A study published by Jason Kovac MD highlights the 2010 meta-analysis published in Fertility and Sterility as the best literature to consider, where researchers reviewed 15 placebo-controlled treatments and 32 reports. The results suggested that soy protein and isoflavones do not affect testosterone levels in men — regardless of age.
There are medications that will block the conversion of testosterone into estrogen and are used in men, but I rarely use these. The best way to balance your hormone levels is to:
1) Be highly fit and exercise vigorously
2) Keep your weight normal
3) Eat a clean diet free of processed foods and chemicals
4) And yes you can have 1-2 servings of soy food daily. The real reason to avoid soy foods is for people with soy food sensitivities. Soy foods are one of the top 5 food intolerances, and if you are soy intolerant, then you should avoid eating soy food.
Steven Masley, MD
Do you ever recommend Nattokinase which is made from soy as a blood thnner?
Nattokinase does have some anti-coagulant activity, but to me the response with Nattokinase isn’t highly precise and might vary between individuals. When I use a blood thinner for a patient with a serious medical condition (heart valve problems, a blood clot, or atrial fibrillation), which can be life threatening, I’m only going to use something that is proven in clinical studies to provide the outcome I want. The challenge is weighing the risk and the benefits and making the right decision for the individual. Every person is different and this must be part of a personalized health care decision.
Steven Masley, MD