The myth: Soy affects your hormones.
The verdict: True—but not in the ways most people think.
Soy contains plant-based compounds called isoflavones, says Dominic Matteo, a partner education lead at Precision Nutrition in Cleveland.
Isoflavones can either increase or decrease your estrogen levels. For example, they can mimic the hormone to improve bone density and they can block it to reduce overproduction and your risks of certain cancers, explains Kipper.
Unfortunately, there's no clear-cut way to know how the compounds will function for you. It depends on several genetic factors, including how much estrogen is naturally in your body, Matteo says.
He can say this: Often-talked-about side effects of soy, like thyroid issues and low testosterone, are typically a result of extreme overconsumption.
For the benefits without the risks, Matteo recommends maxing out at two servings per day. That's about eight ounces of tofu, tempeh, or edamame.
The myth: Soy causes breast cancer.
The verdict: False.
When eaten in mass quantities, soy can increase estrogen levels, and excess estrogen has been linked to breast cancer. People then jump to the conclusion that soy can up your risk of the disease. That said, large-scale science doesn't support the theory, Kipper says.
Take a recent study, which followed more than 50,000 women for almost eight years to see if dairy and soy milk intake impacted breast cancer risks. The researchers found no link between soy and diagnosis.
Still, follow the upper limits Matteo outlines above.
The myth: Soy causes bloat.
The verdict: It depends on the type.
Most of the time, this symptom is caused by highly processed products like bars and vegan meat alternatives, Matteo says. They often contain sugar alcohols and other added ingredients that can be hard to digest.
You may also experience soy-induced bloat if you're sensitive to FODMAPs, a class of carbohydrates that some people struggle to break down. Cooking, soaking, or fermenting these compounds makes the process easier on the body.
For these reasons, Mateo suggests sticking to minimally processed foods (tofu and edamame, say) and fermented ones like tempeh and miso.
The myth: Soy's antinutrients cancel out the ingredient's health benefits.
The verdict: False.
Antinutrients, common in legumes, hinder your ability to absorb carbs, minerals, and protein. Soy contains two: trypsin inhibitors and phytic acid, Matteo says.
These substances can be deactivated through cooking, though fermenting and boiling are the most efficient. To break them down, Matteo recommends boiling ingredients like tofu and edamame before sautéing.