Soy is one of the most controversial foods out there. Depending on whom you ask, you might hear that soy is a miracle superfood. Or, you might hear that it’s toxic and can kill you. Confusing, to say the least!

So what’s the truth? The short answer is that soy can be a healthy choice, in moderation. Here’s what you should know.

Soy comes in many forms. One of the most important distinctions to understand is the difference between whole and processed soy.

As with other foods, the whole version of soy is much healthier. The reason is that your body can absorb all of the nutrients in a whole food. And there are typically no added fillers or preservatives.

Whole soy refers to soy foods that use the whole soybean in its natural state. Examples of whole soy foods include:

  • edamame, or green soybeans (cooked)
  • miso, or soy paste
  • soy nuts, or whole soybeans that have been soaked in water and then baked
  • tofu
  • tempeh

Processed soy is a different story. It’s usually genetically modified (GMO), and contains unhealthy fats and fillers. You can identify processed soy by checking ingredient labels for these terms:

  • soy lecithin
  • soy protein concentrate
  • soy protein isolate
  • texturized vegetable protein
  • hydrolyzed vegetable protein

Whole soy foods tend to be high in protein and fiber, as well as minerals such as zinc. For example, 1 cup of cooked edamame contains a whopping 18.5 grams of protein, 8.1 grams of fiber, and 2.1 milligrams of zinc. Incorporating a whole soy food into your diet can help you feel full without a lot of fat or calories. It can also improve your digestion.

Fermented, organic, whole soy is best

Soy is thought to have some of the highest levels of pesticides of all crops. And many varieties are GMO. For this reason, it’s best to purchase whole, organic soy.

Even better is whole, organic soy that is fermented. Fermentation refers to a process where a food or drink is broken down by bacteria, yeasts, or other microorganisms. Asian cultures have consumed fermented soy for centuries.

Scientists believe that fermentation makes soy easier to digest. It also adds probiotics, or “good” bacteria. These bacteria can boost your overall health and improve your absorption of soy’s disease-fighting phytonutrients.

Smart choices of fermented soy include:

  • miso
  • natto
  • tempeh
  • soy sauces
  • fermented tofu and soymilk

The medical literature reveals a complex picture of soy’s health effects. Much of the data is inconclusive or conflicting. Here are a few of the main takeaways.

Soy may prevent or treat cancer

Soy products contain isoflavones. These compounds are thought to act similarly to the hormone estrogen in the human body. There’s been controversy around whether this hormone-like effect contributes to the development or worsening of cancer, particularly hormone-sensitive cancers like breast cancer.

However, recent research suggests that soy products don’t contribute to breast cancer, and may actually reduce the risk of recurrence. A study in the journal Cancer Investigation even found that genistein, the most common isoflavone in soy, is an antioxidant and helps stop cancer cells from growing and spreading.

Still, the jury is out on how these compounds may affect our hormones, particularly in relation to the female reproductive system. Talk to your doctor about your own situation and risks.

Soy possibly lowers cholesterol

Some studies show a positive effect of soy on cholesterol levels and heart health. Other studies do not. The American Heart Association says that soy protein may lower LDL, or “bad” cholesterol, by about 3 percent. They also advise that soy protein is a good replacement for foods that are high in animal fat.

Dementia concerns

Concerns about the relationship between unfermented soy and brain-related disorders such as Alzheimer’s disease have emerged. A 2014 study warns that soy “cannot be excluded as a possible contributing cause” of Alzheimer’s and other types of dementia. The hormone-like actions of isoflavones are thought to possibly interfere with brain function.

Is soy baby formula healthy?

Health professionals widely agree that breast milk is the best food for babies because of its many nutrients and immune factors. It safeguards babies from illness, supports healthy growth and development, and influences lifelong disease risk.

Baby formula is the alternative when breastfeeding is not possible or ends prematurely. Soy-based formula has caused concern because babies are more susceptible to the estrogen-like effects of isoflavones. However, no specific problems have been documented in babies receiving soy formula.

Soy is also a fairly common allergen, meaning many adults (and even babies) are sensitive to or allergic to it. Try eating a small amount of soy at first to be sure you don’t have a reaction. If you or your baby has a reaction, avoid it and call your doctor.

Talk to your doctor about your personal health history and how soy may or may not interact with it. For most people, whole fermented soy foods can be a healthy addition to the diet and provide important nutrients. As with all nutrition and lifestyle choices, listen to your body and use moderation.