Soy: To Eat or Not to Eat?

Should you be eating soy, or avoiding it? Here’s what the science says about soy foods.


By Liz Thompson


What do you think about soy?

Soy is one of the most controversial nutrition topics. So much research has gone into this area, yet the results are mixed and inconsistent, creating some doubts about the benefits of soy. Does it actually provide any health benefits? Does it cause any harm? Is it linked to cancer, or does it protect us from it? This article will explore soy in more depth and dispel some of the uncertainty surrounding soy and soy foods.

What is soy?

Soy and soybean products have been commonly consumed in some Asian countries, such as Japan and China, for many years. More recently, soy has become popular in the Western diet, especially among vegetarians.

Soy is an excellent source of protein. Unlike other plant proteins, soy is what’s known as a complete protein as it contains all of the essential amino acids ⁠⁠— these are protein building blocks that we must consume from our diet because our body doesn't make them. Soy also provides us with different vitamins, minerals, and fiber.

Compared to meat protein, soy has no cholesterol and most of its fats are heart-healthy, polyunsaturated fats. Soy also comes with well-known phytochemicals (plant nutrients) called isoflavones, which have been the spotlight of much of the research around the health benefits of soy. Doesn't this sound like the perfect food?

Soy food sources

Some examples of soy foods include soy milk, tofu (bean curd), soybeans, edamame, soy cheese, soy burgers, miso, tofu yogurt, and tempeh.

Potential health benefits

Soy is said to reduce the risk of heart disease by lowering the LDL cholesterol (the bad kind) in our bodies, decrease menopausal symptoms like hot flashes, improve bone, brain, and memory health, and even minimize the risk of cancer. Are these health claims valid? It sounds too good to be true, right?

Mixed results

Though much research has been done on the benefits of soy, the results are diverse and sometimes conflicting. Various factors may have led to these inconsistencies, such as differing study designs, type of soyfoods studied, number of subjects, type of subjects (i.e., animal or human), and the length of time that the soy products were consumed.

Soy and your heart

A lower risk of heart disease is seen in China and Japan, and it has been suggested that this is related to the relatively high intake of soy food products in these regions. However, more research is needed before this correlation can be confirmed.

The Food and Drug Administration (FDA) approved an authorized health claim for soy protein and heart disease risk since 1999. However, after this claim was established, studies came out with inconsistent findings about soy and heart health, and in 2017, FDA proposed to revoke the authorized health claim.

However, earlier in 2020, the American Heart Association published a paper indicating the possible link between soy and a reduced risk of coronary heart disease. Overall, the verdict on soy and heart health is still inconclusive.

Soy and menopausal symptoms

Menopausal symptoms, such as hot flashes, are usually caused by low estrogen levels during menopause. Isoflavones — a compound we mentioned earlier that is abundant in soy products — are a phytoestrogen, or plant estrogen, and have a similar structure to the hormone estrogen in our body. Though not exactly the same, there have been hypotheses that eating more soy foods could increase estrogenic activity in the body. It’s even been suggested that soy products be used as a treatment to reduce the uncomfortable and unpleasant menopausal symptoms. However, research from all of these findings is, thus far, weak and inconsistent.

Soy and cancer

There is some research to suggest that women with a higher intake of soy have a decreased risk of developing breast cancer, and possibly even recurrence, when compared to women with a lower soy intake. However, others are concerned that soy foods could increase the risk of cancer due to the isoflavones present in soy. The way isoflavones work in our body is complicated; in some cases, it seems like isoflavones in soy may cause some weak estrogenic activity, but in other cases, they can have anti-estrogen actions. What’s all that about?

According to the American Cancer Society, soy foods are healthy and safe. Experts who study soy generally agree that it’s safe to eat soy foods, and current evidence shows that soy foods appear to be safe even for breast cancer survivors. However, soy in the form of supplements, which can be very high in isoflavones, is not recommended.

Other benefits

Soy has a few other suggested health benefits too. These include its role in improving bone health, insulin resistance, blood pressure, and inflammation, and reducing age-related memory loss and cognitive problems. Again, these health benefits are as yet unconfirmed.

Concerns of soy

We now know of the potential benefits of soy, but are there any concerns that we should worry about? Is soy safe to consume for everyone, or are some people at risk?

Soy and thyroid functions

People may be concerned about how soy affects their thyroid functions. For most healthy adults, consuming soy in moderate amounts should not affect thyroid function. A study found that, for certain people with underlying or existing thyroid problems, certain levels of soy supplementation may interfere with thyroid function. However, this relationship needs to be further investigated. Soy may also interact with thyroid medications, so it’s important for those taking these drugs to seek specific instructions from their doctor about including soy products in their diet. If you want to eat more soy foods but are concerned about a thyroid problem or medication, you should consult with your doctor.

Soy’s effects on men

A common question among men is whether soy foods can cause feminization or infertility in men. It was reported that two men developed feminized effects when consuming a very high amount of soy (around 12 to 20 servings of soy a day).

However, that is an extremely high amount of soy, and other studies among men who consumed a more typical amount per day found no feminizing effects. Remember, isoflavones are not the same as estrogen and soy foods don’t contain estrogen. Isoflavones were also shown to have no effect on the quality of sperm or semen.

Generally, men do not need to worry about consuming soy foods in regular, moderately sized portions.

How to add soy into your diet

Although we still need more studies to confirm all of the health benefits of soy, soy can certainly be included as part of a healthy diet. Here are some ideas for simple ways to include soy in your diet:

-Use calcium-fortified soy milk for breakfast cereal, smoothies, or when making desserts like pudding, cake, or cookies

-Add tofu into soups, stews, and salads

-Steam or boil some edamame as a snack

-Try soy burgers or soy hot dogs for your next barbeque

-Marinate then bake tofu

-Sprinkle some soy nuts onto a salad or yogurt

-Add tofu or tempeh in a stir-fry dish

-Spread soy nut butter on crackers or bread

The bottom line

We still need more standardized research to confirm all of the health benefits of soy. However, there is no doubt that soy is a healthy food choice. It’s a good source of heart-healthy polyunsaturated fats with no cholesterol, and is filled with vitamins, minerals, and fiber.

Soy is an excellent protein alternative to meat, and, as a complete protein source, can be a particularly good option for vegetarians and vegans.

However, while current recommendations state that a moderate portion of soy foods in our typical diet can be beneficial, extremely high intakes or use of soy supplements is not advised, so make sure you’re eating in moderation!

Liz is passionate about helping people improve their health and wellness through lifestyle and nutrition changes, and she is especially interested in diabetes prevention and management. Liz enjoys working with clients to find individualized strategies to improve their health in ways that last. Outside of work, you will likely find her rock climbing, biking, or spending time with her family.

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