Soy: The Good, the Bad, the In-Between

Soy is such a controversial topic in the world of nutrition. People are either for it or against it and I’ve found myself in many debates over this particular bean! Soy has been blamed for everything from thyroid disruption to cancer. Let’s dive into the tofu and see what soy is really all about!

What is Soy?

Soy comes from the soybean, which is a member of the pea family. Originally, soy was cultivated to improve the nitrogen quality of the soil after it had been depleted from growing staples such as rice. It was not generally consumed because of its indigestibility. However, it became popular in Asian cultures in its fermented forms (miso, natto, soy sauce, tempeh) as fermentation made it more digestible.

The way we eat soy in America is very different than the way people in Asian cultures eat soy. For one, we like to over-process everything. I mean, tofu doesn’t naturally come in those white blocks – it doesn’t even look like something you can (or would want to) eat! We’ve turned soy into everything imaginable and far from what it originally was (the soybean) – milk, sausage, bacon, cheese, BBQed soy, protein powders, supplements, even soy baby formula.

Secondly, we tend to overdo it on the soy. It has become particularly popular in the vegan/vegetarian diet since it is a high source of plant protein. But then one must consider….if it’s hard to digest, is the body able to extract enough protein from it? It also has a lot of anti-nutrients such as saponins, phytic acids, enzyme inhibitors, and oxalates. We’ll explore this in a minute.

How Soy is Processed

Processing soy to make tofu is quite funky. It starts with soymilk, which is made from soaked soybeans. The soymilk is then heated and coagulants are added. Hexane solvents may also be added to help extract the oil. Hexanes have known side effects for humans, including dizziness, nausea, headaches, and mucous membrane irritation (1).

In addition, many soy products such as soy flours and protein powders involve chemical extractions during processing.

To get the nutritional benefits of soy, it is best to eat it in its whole form, such as whole soybeans. During the processing of soybeans, byproducts such as soy sauce and tofu lose a lot of their beneficial properties.

The Claims of Soy

You might have heard of soy’s effects on estrogen levels. Soy is a phytoestrogen, which is a plant estrogen. While plant estrogens are similar in structure to estrogen in the human body, it has a weak effect on our estrogen activity.

Soy has been claimed to be beneficial for heart health, hot flashes, certain cancers, osteoporosis, and for containing vitamins and minerals such as A, B12, D, E, and iron. Most of the research on soy is mixed or inconsistent. When considering the research on soy, we have to consider how the research was done as well as other factors such as age, digestion status, and the form of soy that was used.

In addition, one author points out that the soy foods consumed in Asian cultures are whole forms of soy (such as soybeans) while the soy foods studied for research involve soy concentrates or isolated flavones, which could account for the difference in research outcomes of soy consumption (2).

The Pros


Soy boasts high nutrient values – 1 cup contains 65% protein (it is a complete protein, which means it contains all of the essential amino acids we need to make proteins), 43% fiber, and significant amounts of copper, phosphorus, and iron. It also contains moderate amounts of magnesium, selenium, vitamin B6, Vitamin K, folate, selenium, and zinc.

Women’s Health

Many people, women in particular (sorry to call you out, ladies!) tend to shy away from soy because they’ve heard it is estrogenic (and who needs more estrogen these days, right?). However, soy contains phytoestrogens, which are plant estrogens similar to estrogen in the body, but exert weak estrogen activity (3).

Phytoestrogens can actually be beneficial for health, whether you are estrogen dominant or do not have enough estrogen. Several studies show that consuming soy may lead to reduced hot flashes in menopausal women (4, 5). Curious about how phytoestrogens work? Click here for more information.

The Cons

Soy can be hard on the gut because it contains complex proteins and anti-nutrients, which are inherent in grains and legumes and are hard to break down in the body. You might have experienced digestive upset after eating too many nuts or too much nut butter. This is because of those darn anti-nutrients.


Otherwise known as phytates, these anti-nutrients not only make it difficult to digest certain plant foods, but they can also bind to minerals in the body, meaning that we won’t be absorbing those minerals. Minerals that phytates bind to include calcium, iron and zinc, which are essential for bone development, immune health, and energy. And yes, while soy also contains a lot of protein for a plant food, it also contains protease inhibitors, which interfere with protein digestion (6, 7).

Thyroid Function

Soy has been said to negatively affect thyroid function, particularly those with thyroid issues. Soy belongs to a category of plant foods known as goitrogens, which can slow thyroid functioning. This seems to be more of an issue when consuming soy in supplement form or in the presence of iodine deficiency. In addition, goitrogens are deactivated during the cooking process. However, because the research has yet to be super definite on this stance, it is recommended that those with low thyroid function (hypothyroidism) limit their intake of soy products and focus on fermented forms of soy.

Thyroid issues have been shown in babies who have been fed soy formula, suggesting that the formula may be interfering with thyroid hormones. Again, the research is not decisive enough on the issue of whether or not soy isoflavones are harmful for infants. Therefore, many health and pediatric organizations suggest caution when it comes to soy formulas.


As for breast cancer, it is believed that if soy can trigger the growth of healthy breast cells, that it might also trigger the growth of cancerous breast cells. Again, this seems to be more of a concern when it comes to soy supplements, or supplements that contain soy, rather than from food form. It is always prudent to check the ingredients list even on your supplement bottle, as many supplements do contain soy or soy lecithin (8).


Most of the soy produced in the US (80-90%) is genetically modified (GMO), which is another debate. Since we do not yet know how GMOs might be affecting our health and the health of the environment, it is smart to avoid them. Always consume organic soy and always check ingredients. Soybean oil and soy lecithin are hidden sources of GMOs, as well as the feed of livestock and farmed fish.

The Better Side of Soy

We can still reap the benefits of soy in a safer way (aka not in white slimy block form). Consuming whole, organic, and fermented forms of soy in moderation could be nutritious and beneficial for health. Fermentation pre-digests the soybeans, making it easier for us to digest. Fermentation also decreases the protease inhibitors and phytates, making the protein of soy more available and reducing its mineral binding tendency. Be wary of soy supplements and always check the ingredients list if you’re trying to avoid it.


What is your opinion of soy? I’d love to hear your thoughts in the comments below!

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Pouring Hot TeaKatie Dwaileebe at Officer's Row in Vancouver, WA