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Is Soy Protein Isolate Bad for You?

December 17, 2013

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Before you chomp on your next veggie burger or tofu dog, there’s something you should know. Those, and other soy-based foods often considered part of a healthy diet, contain soy protein isolate (SPI), soy’s heavily processed stepchild.

Here’s why you should avoid it.

“There is a lot of controversy around soy and whether or not it’s good for you,” says Devi Moss of Simply Whole by Devi. “But the real controversy lies with soy isolate, not whole food soy products like organic tofu and whole soybeans.”

The health coach steers clear of processed foods, including foods that contain soy protein isolate.

“It is truly best to eat whole foods with all the synergies in the food as opposed to isolating food components,” Moss says.

Generally, soy protein isolate is made from de-fatted soybean flakes that have been washed in either alcohol or water to remove sugars and dietary fiber. This process strips the pure soybean of its nutrients.

“This is a problem with a lot of our foods today,” says Moss. “They have become so manipulated that they’re unhealthy.”

Side effects of soy protein isolate

In animal studies, soy isolate has been linked to allergies, thyroid problems, and even brain damage. Soy has been labeled one of the top seven allergens for people to avoid, as soy isolate is found in a lot of processed foods, including bread and baked goods, soups and sauces, and breakfast cereals and protein bars. There have also been several studies on soy protein and age-related dementia, although many of those studies have been inconclusive. 

Benefits of pure soy

Research shows that roughly 25 grams a day of soy protein is enough to lower LDL or ”bad” cholesterol by about ten percent in people who start out with an LDL above 160. And a comprehensive study on menopause found that two daily servings of soy reduced the severity and frequency of hot flashes. As a healthful meat substitute, Dr. David L. Katz recommends eating pure, non-GMO soy foods such as tofu, edamame, tempeh and soymilk in moderation, meaning two to three soy-based meals per week.  

Opt for fermented soy

Fermentation increases the digestibility of soy, adds good bacteria and reduces the plant estrogen content in soy foods. Fermented soy includes miso, natto and tempeh.

The soy and cancer connection

Dr. Katz says the evidence linking soy intake with breast cancer is mixed. When researchers compare the Japanese, who eat a lot of soy, to Americans, who eat very little, they find lower rates of breast and other cancers in soy eaters. Yet in test tube studies, soy’s plant estrogens accelerated cancer cell growth. One theory is that soy can have both positive and negative influences on breast cancer.

Will you avoid foods with soy protein isolate?