Pros and Cons of Soy: Should You Be Concerned?

Have you been told to avoid soy? Soy has been a staple food in Asian culture for thousands of years. Despite its reported health benefits, soy is often misunderstood and continues to be a controversial nutrition topic.

There are a lot of fears and negative health claims about soy that are important to address. I am not a fan of unnecessarily avoiding nutrient dense plant foods with potential health benefits for no good reason.

So, let’s dive into what we know about soy, the pros and cons and if you should be concerned about including soy into your diet.

Cons

First, let’s take a look at some of the concerns or negative claims that have been made about soy.

1. Increases Your Risk of Breast Cancer?

One of the most common claims is that eating soy can increase your risk of breast cancer.

Soy is a rich source of natural plant compounds called phytoestrogens (isoflavones). It was thought that these plant “phyto”estrogens mimic estrogen in the body.

While estrogen has positive effects on improving menopausal symptoms and bone health, it can negatively increase your risk of blood clots and breast cancer.

Studies in mice demonstrated that when given concentrated amounts of isoflavones that this increased the growth of breast cancer cells and promoted breast cancer tumors. However, it turns out mice and humans metabolize isoflavones differently¹

It also turns out that there are two different types of receptors for estrogen: alpha and beta receptors. These receptors are located in different tissues in the body.

Alpha receptors are concentrated in the liver, breast, uterus, bone, and other tissues while beta receptors are found in the prostate, bladder, colon, immune system as well as the bone².

Phytoestrogens prefer to bind to beta receptors which can explain why they have pro-estrogen effects in the bone, improving bone mass/health and anti-estrogen effects in the breast and uterus, providing protection against breast and endometrial cancers³,⁴,⁵.

One population based study found that soy intake during childhood, adolescence, and adult life were each associated with a decreased risk of breast cancer⁶. Another epidemiological study reported no adverse effects of soy foods on breast cancer prognosis⁷.

Bottomline, it appears soy actually helps to protect you from breast cancer.

2. Soy and Thyroid Function

Animal and test tube studies suggested that isoflavones may reduce thyroid gland function by competing with thyroid hormones for iodine.

More recent findings, however, have shown that soy isoflavones have little to no impact on thyroid function⁸,⁹. The key is to ensure you are getting enough iodine in your diet (or supplementing with iodine).

Food sources of iodine on a plant-based diet include iodized salt, seaweed, dulse flakes (red seaweed salt alternative). You can also take 150 mcg iodine supplement daily.

If you have hypothyroidism and are on thyroid medication (such as levothyroxine), it would be a good idea to wait 4 hours before or after taking this medication to consume soy.

The same holds true for calcium and iron supplements, antacids and cholesterol medication. These can all interfere with the way thyroid hormone is absorbed.

Bottomline if you have thyroid issues this doesn’t mean that you should avoid soy. Just ensure you are meeting your iodine needs and including selenium rich foods in your diet. Examples of selenium sources: 1 Brazil nut, whole wheat pasta, couscous, chia seeds, brown rice, oats, lentils, barley, cashews.

3. Feminizing Effects in Men?

Phytoestrogens are at it again. This time the fear is that soy isoflavones may interfere with the production of testosterone, creating feminizing effects in men.

Earlier studies showed that concentrated isoflavones had estrogen-like effects on male mice, but remember rodents and other animals metabolize isoflavones differently¹².

Meta-analysis, and review of observational and clinical data in humans provide a different picture. Soy isoflavones have no noted effect on testosterone or estrogen levels in men¹⁰,¹¹.

There you go guys. You can enjoy your tofu dinner without the fear of it giving you man boobs.

4. Soy Contains “Anti-Nutrients”

Another concern is that soy – along with most plant foods – contains natural compounds such as phytates, trypsin inhibitors, and lectins.

These compounds are often referred to as anti-nutrients as they are thought to impair the body’s ability to absorb nutrients, vitamins and minerals and cause digestive issues and inflammation.

While it is true that these compounds can interfere with the absorption of certain nutrients, most of these “anti-nutrients” are removed with cooking, fermenting, soaking and sprouting¹³,¹⁴,¹⁵,¹⁶.

Phytates are usually found in fiber rich foods and actually have antioxidant and anti-inflammatory properties. Phytates may provide health benefits such as reducing the risk of inflammation-related chronic diseases such as cardiovascular disease and certain cancers¹⁷,¹⁸.

Another very interesting finding is that a diet high in these anti-nutrients appears to increase the potential of your gut bacteria to naturally break down these compounds¹⁹. Go plant-based eaters!

Soy along with other plant foods containing “anti-nutrients” are staple foods of some of the most healthiest populations in the world. These naturally occurring plant compounds obviously serve a purpose, so let’s stop fretting over them.

5. Soy and GMOs

Most soy grown in the United States comes from genetically modified crops. However, most GMO soy is used for livestock and poultry feed, making soybean oil and as an ingredient in processed foods (lecithin, emulsifiers, and proteins).

According to Our World In Data only 7% of the soy produced globally is used directly for human food products such as tofu, soy milk, edamame, and tempeh. 

Just look for organic or the Non GMO Project Verified label which most whole soy products at the grocery store contain.

6. Soy Allergy

Soy is recognized as one of the big eight food allergens. While soy allergy usually develops in childhood (~0.4% of children are allergic to soy), most of these children (69%) are likely to outgrow their soy allergy by age 10²⁰.

Allergic reactions to soy in adults are rare – estimated to be less than 0.5% of the general population²¹. But, of course, if you have a true allergy to soy you should avoid it.

Pros

After breaking down all of the negative claims against soy, I think it’s time to dig in to all of the benefits soy has to offer.

1. Nutrient Dense

I think this is a good place to start as soy foods are loaded with beneficial nutrients!

Soy is rich in:

• Plant protein: Soy is a complete protein that offers all the essential amino acids.
• Fiber: Soy is rich in both soluble and insoluble fiber.
• Minerals: iron, zinc, magnesium, calcium, copper, manganese, phosphorus, potassium, selenium.
• Vitamins: B vitamins (folate, thiamine, riboflavin, niacin), vitamin K1.
• Omega-3s: good source of essential ALA plant omega-3s.
• Pre and probiotics: Soy is a good source of fiber providing prebiotics (fuel for your gut). Fermented soy (miso, tempeh, natto) also provides probiotic benefits along with better digestibility.
• Polyphenols (phytochemicals): compounds in plant foods that act as antioxidants.
• Isoflavones (a type of plant “phyto”estrogen):  the main compound associated with its health benefits along with its controversial claims.

The healthiest soy foods are those that are less processed such as tofu, tempeh, edamame, unsweetened soy milk/yogurt, soy nuts, miso and natto.

Highly processed soy includes soy protein powders, soy protein isolate, soy flour, soybean oil, texturized vegetable protein, and meat alternatives (fake meat).

It is best to limit these more processed products as they don’t provide the same benefits as more whole forms of soy.

2. Heart Healthy

Including more soy foods into your diet may reduce your risk of cardiovascular disease. This may be due to a variety of factors.

Isoflavones in soy have been linked to helping to reduce inflammation in the blood vessels, improve endothelial function (improving elasticity and blood flow), blood pressure, and cholesterol levels²²,²³,²⁴.

Higher soy intake has been associated with a lower risk of death from cardiovascular disease, stroke and heart attack²⁵,²⁶.

Soy, besides being rich in fiber, is also a good plant source of omega-3 s (ALA). Omega 3s have been shown to be beneficial in lowering triglycerides, blood pressure, and increasing HDL (good) cholesterol.

For more information about the benefits of omega 3s check out the blog: Best Vegan Omega 3 Sources.

3. Improves Menopausal Symptoms

Ladies in the house! We all know that as we age and get closer to menopause our natural estrogen levels start to decline.

Because of this, a lot of us have to deal with unwanted symptoms such as fatigue, weight gain, irritability, insomnia, hair loss, vaginal dryness, and hot flashes to name a few. Doesn’t sound like fun does it?

Since soy is rich in phytoestrogens (isoflavones), they have the ability to bind to estrogen receptors reducing some of these symptoms, particularly hot flashes²⁷,²⁸.

In fact, a more recent randomized controlled trial – the WAVS study (Women’s Study for the Alleviation of Vasomotor Symptoms) – showed some pretty cool results.

They looked at the effects of a low-fat plant-based diet plus the addition of 1/2 cup of cooked soybeans daily on postmenopausal women. Moderate to severe hot flashes reduced by 84% along with improved quality of life²⁹.

4. Can Improve Bone Health

Another problem specifically for postmenopausal women is decreased bone mass and higher risk for osteoporosis with declining estrogen levels.

Since soy phytoestrogens (isoflavones) bind to estrogen beta receptors which can be found in the bone you would expect it to have a protective effect.

The results can be conflicting as a lot of studies used high doses of isolated isoflavone supplements instead of using whole soy foods. But, soy has been linked to reduced bone turnover/loss, increased bone mass and bone calcium retention, and may reduce the risk of bone fracture³⁰,³¹,³²,³³.

Soy is also a good source of calcium and plant based protein both of which support bone health.

In fact, just by having a higher intake of plant protein versus animal protein has been associated with decreased bone loss and risk of fracture and frailty³⁴,³⁵.

Bottomline, there are many things that impact bone health: magnesium, calcium, vitamin D, vitamin K, protein and weight bearing exercise. Eating a nutrient dense diet including soy foods can have a positive impact on your bones.

5. Protective of Certain Cancers

We have already discussed how soy can provide protection against breast cancer. Soy foods have also been associated with reduced risk of other cancers.

Observational studies have shown a 19% reduction in risk of endometrial cancer when comparing highest reported soy intake versus lowest³⁶.

A systematic review and meta-analysis of 23 prospective studies showed that a higher intake of soy was associated with decreased risk of mortality from gastric, colorectal, and lung cancers as well as ischemic cardiovascular diseases³⁷.

For you men out there, soy does not discriminate. Turns out soy foods may also provide protection against prostate cancer, one of the most common cancers among men in the United States.

Observational studies have shown significant association between soy intake and decreased risk of prostate cancer³⁸.

6. May Improve Blood Sugar/Insulin Sensitivity

Soy consumption has been linked to improved insulin sensitivity and glucose metabolism, improved oxidative stress and decreased risk of developing Type 2 diabetes and cardiovascular disease³⁹,⁴⁰,⁴¹.

This can be attributed mostly to the isoflavone content of soy. However, soy is also low in saturated fat and provides a rich source of fiber and plant protein which can also have a positive impact on blood sugar control.

Another study, although small, had interesting results. Partly replacing meat protein with soy protein improved insulin sensitivity and blood lipids in postmenopausal women with abdominal obesity⁴².

Soy, IBS and Gut Health

Another consideration to take into account is if you have irritable bowl syndrome (IBS) or digestive issues.

Soy can be great for gut health. It is high in both insoluble and soluble fiber. The soluble fiber provides fuel for the healthy bacteria in your colon.

In fact, some studies have shown that soy can help increase the levels of healthy bacteria and reduce the levels of bad bacteria creating a healthier microbiome⁴³,⁴⁴.

If you tend to have digestive issues with soy, you may do better choosing fermented sources such as tempeh and miso for improved digestibility and absorption.

FODMAPs

The fiber in soybeans and soy products can also be a source of FODMAPs (fermentable oligo-saccharides, di-saccharides, mono-saccharides and polyols).

FODMAPs are certain types of carbohydrates (starch, fiber, sugars) that are resistant to digestion. Once they reach your colon your bacteria digest them as fuel. This produces hydrogen gas and sometimes draws fluid into your intestines creating symptoms.

Not everyone is sensitive to FODMAPs but they can cause issues for those with IBS or other digestive issues.

So, while soy can be beneficial for a healthy gut certain people following a low FODMAP diet may need to limit certain soy foods for a short period of time while their gut is healing.

Not all soy is high in FODMAPs though. It depends on the maturity of the bean, the processing involved and if it’s fermented or not.

The following soy products are lower in FODMAPs. These foods can be included (in the serving size listed) if following a low FODMAP diet:

• Firm or Extra Firm Tofu (1 cup)
• Tempeh (100g or about 1 slice)
• Edamame, unshelled (1 cup or 90g)
• Miso (2 Tbsp)
• Soy sauce (2 Tbsp)
• Soybean oil
• Soy lecithin
• Soy milk made from soy protein (1 cup or 250ml). *However, most soy milk in the U.S. is made from soy beans and is considered high in FODMAPS.

How to Add Soy to Your Diet

As long as you don’t have a soy allergy or sensitivity to FODMAPs, the addition of soy to your diet can be beneficial to your overall health.

Here are a few ways you can add soy to your diet:

• Make soy milk the base of your smoothies, shakes, chia pudding or topper to your cereal or coffee.
• Add marinated baked or air-fried tofu or tempeh to stir-fries, buddha bowls, tacos, sandwiches, wrap, salads.
• Use ground baked tempeh in chili, soup, stews, enchiladas, tacos.
• Tofu veggie spring rolls, tofu scramble
• Use miso in salad dressings, sauces, and soups.
• Add cooked shelled edamame as a topper to salads, pasta, stir-fries or eat as a snack with lemon juice and coconut aminos.
• Grab some dry roasted edamame or soy nuts for a snack.

Pros and Cons of Soy: Bottomline

The topic of soy is HUGE! With so much misinformation about soy, it’s no wonder why people are confused.

In the end, the pros of soy definitely outweigh any cons. There are so many positive health benefits to adding soy to your diet.

So, how much is recommended? Just like with any food, if you over-consume in huge quantities it can create problems. But, for most people, including 3-5 servings a day of whole soy foods can be a safe daily amount to aim for.

Soy is a staple food for most plant-based eaters. For meat eaters, it appears substituting some whole soy foods in place of meat can have a positive effect on your health.

Bottomline, what really matters is the quality of your overall diet and not just singling out one food or nutrient. Adding soy can be a healthy bonus to a whole foods diet that includes a lot of plants.

For ideas of how to include more plant foods into your diet, read the blog: 15 Tips for Eating More Plants. Interested in getting started on a plant-based diet but don’t know where to start? Check out my Starter Guide + 5 day meal plan.