Soy and Human Health

Alright, we are back with a nutrition post this week, and a controversial one at that. This is a topic I’ve been excited to write about for quite some time now because I get a lot of questions about my opinion of soy. I think there is a lot of fear around soy, and the funny thing is, almost everyone eats it (more on this later). I will warn you now that this is my longest post yet, and I still didn’t cover everything I could have! I tried to touch on what I believe is most relevant and answers the most common questions, and I’ve linked some additional readings at the bottom if you want to learn more.

What is Soy?

The soybean is a legume originating from Asia and it has been a staple in traditional Asian diets for centuries. Traditional, minimally processed sources of soy can typically be categorized as either fermented or non-fermented. Fermented soy products include tempeh and miso, while non-fermented include tofu, edamame, and soymilk.

Nutritional Breakdown

Nutrition Facts for Edamame (young soybeans)

Soy is a complete protein, meaning it has sufficient amounts of all essential amino acids needed for human health and therefore has comparable protein quality to meat. It is moderately high in fat, with a blend of unsaturated and monounsaturated fat, and a small amount of plant-based saturated fat. It’s even a source of omega-3 fat, an essential fatty acid that is anti-inflammatory and required for proper growth. Soy is also a great source of many nutrients you’d find in meat and dairy products, such as calcium and iron. The nutritional profile of soy makes it an excellent meat substitute because of the similar nutritional profile, without the high saturated fat content and cholesterol found in meat. Not to mention it’s a great source of fibre!

What about Phytoestrogens?

A controversial component of soy and soy products is the presence of phytoestrogens, but what is a phytoestrogen? Phytoestrogens are chemical compounds that mimic estrogen in the body because of their similar chemical structure, and therefore can somewhat compete with or inhibit estrogen in the body. Isoflavones, a class of phytoestrogens, is the specific compound found in soy and the term used in most research literature (including the research discussion below).

It is well-known that soy contains phytoestrogens, but did you know you are already consuming phytoestrogens? Another class of phytoestrogens is found in lignans and their metabolites, and also weakly mimics estrogen in the body. Lignans are found in many common foods such as flax seed, many fruits and vegetables, whole grains, and other legumes and seeds. Despite the fear of soy and its phytoestrogen content, lignans are actually commonly consumed in North America and comprise most of the phytoestrogens consumed by individuals!

Despite the controversy and fear of phytoestrogens in soy, most literature reviews (AKA an academic review of multiple research studies on a specific topic) conclude that phytoestrogens actually have anti-cancer and anti-tumor effects on the body, and therefore are not something to fear. Many of these studies even use phytoestrogen supplements as opposed to soy foods, so the dosages used would be much higher than what would be consumed in a glass of soymilk or a serving of tofu. Table 1 here shows the isoflavone content per serving for various soy foods (for reference, most Asian populations consume 25-65mg of isoflavones/day).

The Research on Soy

I really wanted to dive into some research before writing this post to ensure I was sharing accurate and up-to-date information on the topic. Below I will share the more conclusive evidence that has been found regarding soy consumption. However, many topics related to human health and soy are inconclusive still. This isn’t to say that soy is bad – most research is finding either positive effects on health or no effect at all, and very little research actually shows negative health effects. Despite the large number of studies conducted regarding soy, the results are mixed because of different study designs, health measures, soy amounts/sources/administration, and different lengths of study. Because few studies follow similar study designs, comparing their results and making informed, conclusive statements isn’t possible at this point.

For example, I looked into some research about the relationship between soy and male fertility. By review, many researchers were able to conclude that a diet high in fruits and vegetables and low in animal products increases sperm motility. One study showed that high consumption of red meat, soy, and sweets decreased sperm motility – but the rest of the studies were inconclusive or had mixed results (positive and neutral effects). Because of this, it is difficult to offer practical suggestions such as, how high is considered high consumption? What type of soy products did they test (i.e. soy isolates, whole-food soy like soybeans, processed soy like soybean oil, fermented vs. un-fermented soy)? Many of the studies also look at isoflavones as opposed to whole-food soy directly, so it is difficult to generalize the study results to soy food.

Interestingly, many studies regarding soy and human health find that studies in/including Asian populations have stronger positive results. It isn’t understood why, but it could be because of the inclusion of soy traditionally in the diet, they have favorable gut bacteria to metabolize soy optimally, they eat more minimally processed soy and more variety, or because they naturally eat diets high in fruits, vegetables, and grains and low in meat. Despite these possibilities, the health of Asian populations consuming traditional diets is something to be noted when considering optimal nutritional health.

Health Benefits

I will be honest that I really tried to not be biased with this article. Since I eat soy products and enjoy them, it would have been easy for me to disregard science that is anti-soy. I was pleasantly surprised to find that the most recent studies and review articles are actually in favor of it! Although there is a mix (some look at soy directly while some look at isoflavone intake), this is the conclusive research I have found related to soy.

Cancer, one of the most controversial illnesses especially related to soy, actually seemed to benefit from isoflavone intake and soy. I found review articles and studies specifically discussing colorectal and GI cancers and breast cancer. For colorectal and GI cancers, high isoflavone intake was associated with a significantly decreased risk of cancer. Soy is a source of isoflavones/phytoestrogens, so the association between soy itself and a decreased risk of cancer is evident, but weaker. Soy, and in particular the soy isoflavones, have also been shown to potentially lower the risk of breast cancer, including hormone-mediated breast cancer. Isoflavones have been shown to produce antioxidant properties, inhibit tumor growth and cell angiogenesis (blood vessel growth), promote cell apoptosis (cell death), and decrease circulating free estrogen by competing for estrogen receptors in the body.

In case you haven’t heard enough about gut health lately, some studies have actually shown that the metabolites produced in the digestive tract after consuming soy can have beneficial effects on waist circumference, especially in those with metabolic syndrome. However, an unhealthy gut microbiome could mean you have insufficient gut bacteria to metabolize soy optimally, and not reap the full benefits of these metabolites (another reason to prioritize your gut health!).

Finally, the most conclusive data I found related to soy consumption and health is with blood cholesterol. Because the scientific evidence is so strong, Health Canada has approved a health claim related to soy intake to be used on food labels. The food product must meet certain criteria, such as containing a minimum amount of soy protein, to use the health claim on the label (however, this label is usually used on processed food which may not be the most healthful source of soy… more on that later).

These studies have provided conclusive evidence that 25g of soy protein per day can reduce blood cholesterol levels and, because high cholesterol is linked to heart disease, can therefore decrease the risk of heart disease.


Health Concerns

Of course, there are some popular concerns regarding soy intake; one of these is undoubtedly GMO soy and its safety. GMO’s are a hot topic for the environmentally- and health-conscious; they are new, researched very little, and even banned in some countries. I will do a post in the future about GMO’s, but currently I’ve done little research and my knowledge is quite limited. Most of the research regarding GMO’s is funded by the very companies that produce and market the crops, so it’s difficult to discern biased information from unbiased. Additionally, GMO’s have been on the market for a very short period of time, so long-term human health studies haven’t been conducted. However, animal studies have been done which showed alterations in gut bacteria, digestive enzymes, and liver metabolism. How much we can generalize this information to human health and disease progression is unclear though.

Interestingly, many people that fear soy products because of GMO soy are probably consuming it already. Yup. You heard that right. Minimally processed soy products actually marketed as soy (i.e. soybeans, edamame, soymilk, tofu, tempeh) are almost always non-GMO. However, many processed foods (think crackers, cookies, salad dressings, sauces, deep-fried fast food, etc.) on the market contain processed soy as a food additive, and therefore are probably using GMO soy. Why?

The US is currently the largest soybean producer in the world, and almost 95% of it is genetically modified. Because the US produces GMO soy in such a large abundance, it is very cheap to refine into food additives: soybean oil and soy lecithin being two of the most common. These soy additives are usually used because they are cheap and can provide desirable food properties or shelf stabilization to the product. Because of this, those consuming a typical Western-style diet of processed and fast food actually consume tremendous amounts of processed, GMO soy – some estimate that 1/5 of calories in the typical Western diet is soy. How harmful this actually is isn’t clear, however I would personally be skeptical of this unnatural, processed, GMO soy consumption. Eating soy in a minimally processed, natural state, much like the soy that was consumed in Asian populations for centuries, arguably is the most healthful way of consuming soy and reaping any benefits it may have.


There is so much more that can be discussed, so I’ve attached some extra readings below if you want more information on this topic. What are your thoughts on soy? Is there any questions or concerns you still have? Let me know below, here, or on Instagram or Twitter.

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Talk soon friends!


Extra readings:


Obviously, this blog post does not substitute for professional health recommendations; if you have a serious medical condition, especially related to thyroid or hormonal health, I would still recommend talking to your physician and Registered Dietitian to determine your individual needs.


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