Soy foods have gained widespread acceptance in the U.S. and globally. Traditionally a century-old staple in Asian cuisine, soy foods are a nutritious and beneficial addition to your diet. Soy protein is high-quality, providing many essential amino acids that the body needs, among other health benefits. And soybean oil is the most widely used edible oil in the U.S - not to mention, it's heart-healthy.
Despite soy's rise in popularity, a lot of confusion surrounding whether it is "good" for you still exists. Many of these questions, such as "why is soy bad for males?" or "does soy increase estrogen?" are primarily based on outdated animal studies, many of which don't provide clear evidence regarding soy's impact on humans. Let's break down the truth about soy and separate myth from fact once and for all.
Myth: Soy affects reproductive health.
This question is often asked because soybeans contain isoflavones, which are compounds classified as phytoestrogens and mimic estrogen in structure. This has sparked a variety of concerns, particularly among men, about hormone disruption or feminization caused by soy products.
While these myths do stem from real (but very outdated) studies done on two male volunteers wherein researchers found a slight increase in estrogen; if you eat a balanced diet, you likely have nothing to worry about. It turned out that both subjects were consuming almost nine times the amount of isoflavones as the average man living in Japan!
Fact: Current studies show no link between soy intake and changes in male hormone levels.
Myth: Soy causes fertility issues.
While some people believe that soy can harm the female reproductive system or even a male’s sperm count, none of the various studies done on this topic found any link between infertility and soy consumption.
Fact: Soy intake has been associated with positive outcomes in fertility treatment settings.
Myth: Soy is bad for your thyroid.
The myth that soy negatively affects your thyroid comes from outdated in vitro studies and experiments on rats.
Fact: According to new data, there’s no evidence that soy consumption negatively affects your thyroid or metabolism. In people with normal thyroid function – and even those with hypothyroidism – moderate soy consumption poses no apparent risk.
Myth: Soy causes breast cancer.
Because isoflavones act like weak estrogens, there is speculation that soy might pose an increased risk for breast cancer. This concept has raised concerns about the safety of the amount of estrogen in soy products. But actually, numerous population studies show a lower rate of breast cancer in countries where soy consumption is higher.
Fact: There is no credible evidence suggesting that tofu, soy milk, or other soy-based products cause or worsen breast cancer; however, multiple cancer research organizations have come to the conclusion that soy is safe for women with breast cancer. And evidence suggests that soy may even reduce the risk of breast cancer.
Myth: Soy causes poor mineral absorption.
Some soy foods, like tofu and tempeh, contain iron, zinc, and calcium. Because of this they may be popular meat and dairy alternatives for plant-based consumers. However, soy is high in a compound called phytate, which can negatively impact the body’s ability to absorb zinc and iron. The effect is minor for most people – so if you eat a plant-based diet, you might want to add additional zinc-rich foods or take a supplement to combat the phytate.
Fact: Studies have shown that iron and calcium absorption from soy is comparable to that from animal products.
Myth: Soy allergies are common.
Like any food, soy can cause a reaction in sensitive individuals. While soy is one of the top nine allergens (nine which are responsible for 90% of all allergic reactions in the United States), soy allergies are among the least common.
Fact: Less than one percent of all children have a soy allergy – and 50% outgrow it by age 7.
Myth: Soy-based formulas are unsafe for infants.
Soy-based infant formula (SIF) has been safely used for over 60 years, with an estimated 20 million Americans having used soy formula at one point in time. Even though it’s popular, some parents avoid SIF due to the myth that it’s unsafe.
Fact: Multiple reviews, including one from the U.S. National Toxicology Program (NTP), have concluded that SIF is safe for healthy infants, even during key developmental stages.
Myth: Soy causes early puberty.
The theory that soy causes early puberty in children has not fully been supported by scientific evidence.
In a study following prepubescent boys, eating moderate to large amounts of soy was associated with developing pubic hair earlier than the group that ate less soy. However, the study didn’t find any link between eating soy and growing facial hair, which was the secondary measure of puberty onset, debunking this theory.
Fact: Studies show that soy consumption does not affect the timing of puberty in girls or boys in any significant way.
Myth: Processed soy products are bad for you.
From tofu and soy milk to soy protein bars and meat substitutes, processed soy products remain a safe and nutritious part of the diet. The food industry has been adding soy protein to its products for decades due to its safety and texture.
Fact: The presence of soy protein in foods does not translate to an increase in health risks.
Want to learn more? Download our full soy myths and facts brochure
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