Soy has long been a protein staple in many vegan and vegetarian diets, or those just looking to be more plant-based. But as soy and soy products have risen in popularity, so have myths and rumors. That’s why we spoke with Denice Taylor, a registered dietitian nutritionist on the staff at Texas Health Arlington, to understand more about soy, how it works in our body, and to finally see if there’s any truth to some of its most damaging myths.
The Confusion Surrounding Soy
Soy is a legume (part of the bean family) that is an excellent source of high-quality protein, but because it’s also a plant, it has the added benefit of fiber. It’s also one of the very few nutritionally complete plant proteins, meaning it has all nine essential amino acids.
Taylor adds that soy foods are naturally low in fat and do not contain saturated fats, meaning they can be great for someone who is watching their cholesterol or on a low-fat diet. In fact, having soy as a regular part of your diet could help lower bad cholesterol in the body and improve vascular function. And it’s due, in part, to a compound found in soy called isoflavones. But ironically, isoflavones are also the main culprit when it comes to many of soy’s bad press due to the compound’s reported effect on hormones.
One of soy’s biggest myths is related to its reported contribution to the development of breast cancer. The reasoning is that high levels of estrogen help contribute to many hormone-associated cancers, such as breast cancer, and isoflavones in soy are structurally similar to estrogen. But a 2019 review of studies indicated that the isoflavones in soy may help reduce the growth and spread of hormone-associated cancer, including prostate cancer and some breast cancers.
However, according to the American Cancer Society, it is not clear if more processed soy products — such as soy protein isolates or textured vegetable protein — offer the same benefits for cancer prevention as whole soy foods.
“’Soy confusion’ has been around for a number of years with many of the clinical research studies showing its safety as a healthy food,” Taylor says. “But some of the misunderstanding stems from its main ingredient which is an isoflavone. Isoflavones have a chemical structure similar to estrogen; this is where the term phytoestrogen has originated. But phytoestrogens are not the same thing as female estrogens. To be clear, soy foods do not contain estrogen.”
Though high levels of estrogen have been linked to an increased risk of breast cancer, and soy does contain plant estrogens (isoflavones) foods like tofu, edamame or soy milk don’t contain high enough levels of isoflavones to increase the risk of breast cancer. As for the rest of the soy products, the research just isn’t there.
According to the same 2019 review of studies, soy isoflavones may also reduce the risk of diabetes, though the mechanism through which they may achieve this is still unknown.
In type 2 diabetes, the cells of the body absorb less sugar from the bloodstream, which leaves it to circulate and cause harm. Insulin is a hormone that allows blood sugar, or glucose, to enter the cells so that they can be converted into energy. Soy isoflavones may improve insulin sensitivity, meaning that the cells respond more to insulin and absorb more glucose.
Soy has a bad reputation for a few reasons. It’s the top GMO food produced in the United States. According to the World Health Organization (WHO), genetically modified organisms (GMOs) are “organisms (i.e. plants, animals or microorganisms) in which the genetic material (DNA) has been altered in a way that does not occur naturally by mating and/or natural recombination.” According to the USDA, in 2014, farmers used 94% of soybean farmland in the U.S. to grow genetically engineered soybeans.
Despite concerns about GMO crops, the WHO also state that “GM foods currently available on the international market have passed safety assessments and are not likely to present risks for human health.” Although the impact of GMOs on humans continue to be highly debated, if it does concern you, you can stick with 100% organic soy products or products that specifically label they do not contain GMOs.
There is also some concern that soy intake may interfere with thyroid function. Soy contains goitrogens, which are substances that can negatively impact the thyroid by blocking iodine absorption. In one 2016 study of 548 women and 295 men who ate soy foods as part of a vegetarian diet, researchers found that women with higher soy intake had a higher chance of having elevated levels of thyroid-stimulating hormone (TSH). A high TSH level may signify an underactive thyroid. Researchers did not find the same results in men.
The authors explain that soy is likely to be safe. However, consuming excessive amounts may create health risks in some people, such as those with undiagnosed hypothyroidism.
Another potential downside to soy is the fact it can be a common allergen for many people. A soy allergy often starts in infancy with reaction to soy-based infant formula. Although most children outgrow a soy allergy, some can carry the allergy into adulthood.
Mild signs and symptoms of a soy allergy include hives or itching in and around the mouth, and in rare cases, soy allergy can cause a life-threatening allergic reaction called anaphylaxis.
If you are allergic or suspect you’re allergic to soy, you should avoid all products that contain soy.
Like all foods, soy should be eaten occasionally and in moderation rather than all the time. When consuming soy, stick with non-GMO options, or whole soybean products. If you have a history of breast cancer, hypothyroidism, or an underactive thyroid, talk to your provider about what intake is best for you.
Go for two servings a day, which is 1 cup of edamame, 3oz of tofu, or 1 cup of soy milk.
Overall, soy has many health-protective benefits. If you are someone who suffers from diabetes or cardiovascular disease, then adding soy into your diet, while removing saturated fat and protein can be a smart move. While more research is needed, soy is a healthy addition to any balanced diet.
“If you are concerned about your health and you like soy foods, stick to the most natural soy foods, such as soybeans, tofu and soy milk,” Taylor adds. “Soy foods are healthy and as with all foods, the less processing the better the food is! Additionally, people that eat soy foods may also be more likely to eat more fruits and vegetables and avoid high-fat processed foods. Adding up the benefits of a healthy diet, along with soy foods and physical activity can go a long way in a healthy lifestyle!”
And if you need more convincing, consider that Asian cultures, known for being some of the healthiest in the world, rely on soy for a large part of their diet.
Looking for more information on plant-based proteins? Check out our articles below: