The Health Benefits and Side Effects of Soy

by Ahmed Zayed, MD on September 23, 2020
Last updated on May 23, 2021

The soy production in the US did not blossom until after World War II had ended. It was then that the FDA first approved the use of soybeans. It was also the time when the FDA confirmed that soybeans are beneficial in the fight against heart disease. Nowadays, we have the perk of choosing between the many different soy products. Whether it is fresh edamame, soy milk, or soy supplements, there is more than one way to gain the benefits that these little legumes have to offer. In the following, we will be discussing both the benefits and the possible side-effects of soy.

Types of soy

Soybeans are available as whole or processed in many different forms. Talking about whole soy products, these are the ones to choose from. Soybeans and edamame are the least processed soy products of them all. This makes them one of the healthier options out there. Soy milk and tofu are safe as well as they are produced by using whole soybeans.

There are many fermented soy products available on the market today. Such include soy sauce, miso, tempeh, etc. But soy is also used to produce many processed soy products. Vegan cheese, vegan yogurt, and vegan meat substitutes often have soy as their primary ingredient.

Soy supplements are available as well. Many vegetarians and vegans are enjoying soy protein isolate to secure proper protein intake. Other popular options are soy isoflavones and soy lecithin supplements, available in the form of capsules and/or powder.

The health benefits of soy

Without further ado, here are the most popular benefits of regular soy intake. We will be talking about some of the greatest myths and misbeliefs, while also sharing reliable scientific proof to support our findings.

It is rich in several nutrients

One of the reasons why soybeans are so popular among vegans and vegetarians is because they represent a complete protein. When we say complete protein, we mean that all of the nine essential amino acids are found in soybeans. 100 grams of cooked soybeans contain around 12 grams of protein.

But protein is not the only nutrient found in soybeans. Soybeans contain very little unsaturated fats while being a great source of Vitamin C, folate, calcium, magnesium, iron, thiamin, and many other much-needed nutrients. One of the more important nutrients found in soybeans is a prebiotic fiber. Several phytochemicals, highly beneficial for one’s health, are found as well (1).

It may regulate cholesterol levels

Researchers suggest that soybeans can help regulate cholesterol levels. These effects are greater in those diagnosed with high cholesterol levels. But for these effects to be achieved, one is supposed to eat pure soybeans instead of soy supplements (2).

Another review published in 1995 found that 47 grams of soy, per day, was enough to reduce the total cholesterol level by 9.3% and the “bad” cholesterol levels by 13% (3). This is certainly good news considering the potential health risks caused by high cholesterol levels.

It may improve fertility

Talking about soy and fertility, the results are quite conflicting, to say the least. A study published in Fertility and Sterility showed that soy has helped achieve better outcomes in women undergoing assisted reproductive technology (4). Similar results were achieved in women undergoing in vitro fertilization (IVF). A diet rich in soybeans has supported a more successful pregnancy, according to a 2016 study (5).

But then research published in the Journal of Nutrition has published quite the controversial results. Apparently eating high amounts of soy could negatively affect the ovarian function by altering the reproductive hormone levels (6). Yet another study showed that a diet rich in soy lowers the chances of women to carry a child (7). Knowing all of this, it is best to consult a medical practitioner regarding your soy intake before and during pregnancy.

It may reduce menopause symptoms

Soy is said to help relieve many of the common menopause symptoms. It is all explained through the presence of isoflavones which are naturally found in soybeans. Isoflavones resemble a weak estrogen in the body. As you may know, during menopause, the body goes through a natural decline of estrogen levels. These hormonal changes are guilty of the many uncomfortable symptoms present during this period of life.

A review showed that the use of soy isoflavone supplements has helped relieve the menopause symptoms by as much as 14% (8). Similar results have been achieved in a 2012 study (9). It seems that hot flashes is the most common symptom relieved thanks to the use of soybean isoflavones.

It may help weight loss

Despite the lack of human studies, soy is believed to help manage a healthy weight. As a 2019 study explains, the soybean isoflavone supplements have helped experimental rats to maintain a healthy weight (10). The supplements helped reduce the fat build-up around the organs which is believed to be the reason for maintaining a healthy weight. More research on this topic is awaited.

It may prevent hormone associated cancers

When it comes to hormone associated cancers, such as prostate and breast cancer, soybean isoflavones might be able to help. A review published in Nutrients talks about the possibility of soy isoflavones being used in the prevention of hormone associated cancers (11). According to some researchers, soy has helped Asian women to reduce their risk of breast cancer before and after menopause.

It may help with muscle growth

Being a complete protein, soybeans are often the primary protein source for vegans and vegetarians. The protein found in soybeans is also quite similar to the animal protein. Being rich in one specific essential amino-acid, L-arginine, soybeans help your body to burn more fat and instead build more muscle during your workouts. If you are looking to build some lean muscle, soybeans are a must in your diet.

But if you find it difficult to eat more soybeans on a day-to-day basis, we would recommend a soybean isolate protein supplement. This one is easy to combine with your other meals and is often available in many different flavors. You just need to do your research and find your favorite one.

It may reduce the risk of diabetes

Yet another beneficial effect of soybeans is the reduced risk of diabetes type 2, as the 2019 review that we mentioned before explains. Although the overall mechanism of action is unknown, it is said that isoflavones do a great job of improving insulin sensitivity. This may as well be the factor that keeps diabetes away from us.

It may help you beat insomnia

If you are struggling with insomnia or any other sleep issues, you may want to try soy. What is interesting is the high concentration of magnesium found in soybeans. Perhaps you did not know this but magnesium is an important nutrient that helps secure a good night’s sleep. Scientists suggest that increasing one’s magnesium intake can help elevate insomnia symptoms. It may also help to wake up easier in the morning. This is especially important for any sleepyhead out there that has trouble to stop hitting the snooze button. If you want to sleep like a baby, give soybeans and magnesium a try.

It may help treat osteoporosis

And last but not least important, the soy isoflavones may be beneficial against osteoporosis. It is said that these isoflavones may represent a good alternative to the usual hormone replacement therapy used to treat osteoporosis. We mentioned that isoflavones act as a weak estrogen in the body.

In women, osteoporosis is mainly caused by estrogen deficiency. By increasing the estrogen levels, through an increased intake of soy isoflavones, it is possible to reverse the process. A similar effect is achieved by using hormone replacement therapy. This would explain the theory that suggests soy isoflavones as a potential treatment for osteoporosis. However, this is still a topic that needs a lot more investigation done on and as such, remains a mystery.

The potential risks of soy

Research so far shows that unless you have a soy allergy, eating soybeans a couple of times a week will not expose you to any great health risks. However, we like to look at everything with a critical eye. That being said, here are the potential health risks linked to the use of soy and soy products.

It may contain GMOs

One of the biggest concerns about soy and soy products is GMO. According to the FDA, up to 90% of the soy found in the US is genetically modified (12). Talking about GMOs, there is still a lot of controversy tied to such products, discussing the many potential side-effects (13). As such, researchers often remind us to avoid any GMOs until their true role in terms of human health has been revealed.

Being genetically modified, soy may not be the best product to choose if you want to preserve your good health. If you still choose soy for its potential health benefits, make sure that you are choosing non-GMO soybeans. Look carefully for the non-GMO sign on the packaging and do your research.

It may reflect poorly on thyroid function

Being genetically modified is not the only concern when it comes to soy and soy products. Many researchers suggest that soy can negatively impact thyroid function and pose certain risks. The reason is soy being rich in goitrogens which are substances with a potentially negative effect on one’s thyroid gland. They are blocking the absorption of iodine which is an essential nutrient, important for a proper thyroid function.

Some researchers also suggest that these substances can also interrupt the production of thyroid hormones (14). Without the necessary thyroid hormones, many body functions are at risk. And then there are the researchers that suggest that soy has no negative effect on the thyroid function whatsoever. One specific study found that those with hypothyroidism have nothing to worry about as long as they intake sufficient iodine (15).

It may affect testosterone production

One of the common reasons why men tend to avoid soy is because they fear that it will interrupt their testosterone production. This belief originates from the presence of phytoestrogens found in soy. While these may help increase the estrogen levels in women, this would not be the wanted effect in men.

However, many scientists agree that soy does not affect testosterone production. There is also no scientific proof that would say otherwise. In fact, a 2010 review investigated the use of soybeans, soy products, and soy supplements in terms of the testosterone production in men. The results did not reveal any significant declines in the participants’ testosterone production (16).

It may have a negative effect on digestive health

Some have said that soybeans are the cause of poor digestive health. Several animal studies could confirm that, although there are still no human studies done on the topic. The cause seems to be the agglutinins found in soy. These are antinutrients that have been linked to a line of potential side effects, some of which are digestive issues.

These substances are said to harm the gut microbiome and the barrier of the gut. In animal subjects, they have increased the intestinal permeability which has caused harmful substances to easily enter the digestive tract (17). Luckily, these digestive issues seem to be prevented by the proper cooking process of soybeans. This helps to decrease the number of antinutrients found in soy and increase its digestibility.


It seems that soy has a lot more health benefits to offer than we originally thought. From insomnia, muscle growth, heart disease, and even cancer, to diabetes, the list of benefits is quite a long one. But there are also those who are doubtful of benefits and weigh them against the possible risks. In today’s article, we discussed both sides. That way you have all the information that you need to make a firm decision. Does soy have a place in your diet or perhaps it does not?


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