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What Is Soy Protein Isolate and Is It Bad For You?

We talked to nutrition experts to find out how safe it is to consume products with SPI on the label.

Between the portions, grams, percentages, tiny as heck print, and fifty-plus nicknames for sugar, reading a nutrition label can make anyone feel like they're decoding a lot of gibberish.

But if you're vegan or start swooning anytime a menu features the Impossible Burger, there's one term of nutritional mumbo jumbo you should probably know: soy protein isolate (SPI).

That's why we called on Eat This, Not That! go-to nutritionists Jonathan Valdez, R.D.N., owner of Genki Nutrition and spokesperson for the New York State Academy of Nutrition and Dietetics and Lisa Richards CNC, nutritionist and founder of The Candida Diet to explain what the SPI is, and whether or not it's healthy.

What is soy protein isolate?

At risk of sounding like Captain Obvious, SPI is protein from soybeans that's been isolated from all the other ingredients in soy. "It's what remains when you take soybeans and strip all the sugars, fiber, and other natural vitamins and minerals from them, leaving only the protein" says Valdez.

Made through a process called acid-washing, soybeans get soaked in acid or alcohol to remove the sugar and dietary fiber. Then, what's left gets dehydrated which ultimately makes a dry powder that looks like any 'ole protein powder.

"The end result is an incredibly protein-rich product that's cholesterol-free, and contains very little carbohydrates or fat," says Valdez. Because of that, it's often used in products like soy-based infant formula, protein bars, flour, cereal, and meat and dairy alternatives to boost protein content without increasing the carbs or calorie count, he says.

The pros and cons of soy protein isolate

No doubt, SPI is a super high-protein substance. And that's exactly why vegetarians or vegans, and those allergic to cow's milk, may use products with SPI, says Richards.

But unfortunately when it comes to SPI, it's not as simple as: it's high protein so it's healthy. That's because the process the soybeans go through in order to create the high-protein product is controversial.

"The extraction process often leaves behind residue from chemicals and metals like hexane or aluminum," says Valdez. So if you consume SPI you're likely noshing on at least some of these "leftovers". While he says the amount of metal you'll encounter from SPI is unlikely to be toxic, it's generally considered good practice to limit the amount of metals in your diet where possible because in high levels they can be toxic. And things like gasoline fumes, quick-drying glue, spray adhesives, contact cement, arts and craft paints, and stain removers all expose us to these not-so-savory chemicals on a daily basis, according to Valdez.

There is another reason why some experts side-eye SPI: "It contains phytates, also called anti-nutrients, which reduces the body's ability to absorb iron and zinc," says Richards. Note to mention, the extraction process strips the powder of the zinc and iron typically present in soybean products. Is this a double-whammy? Sure. But so long as you're consuming legumes or red meat, which contains zinc and iron, you really don't have to worry about a micronutrient deficiency from SPI.

"Another thing that adds to the SPI controversy is that they are genetically modified foods," says Richards. This shouldn't be surprising: at least 90 percent of the soybeans grown in the United States are genetically modified. So of course most SPI is, too!

Why is this a problem? Some say it's not, and Valdez says, "There's currently no scientific evidence showing that non-genetically modified foods are any healthier than genetically modified ones." But some folks claim GMO's have an inflammatory effect on the body and can exacerbate the symptoms associated with inflammatory disorders like arthritis, asthma, and Crohns.

Should I avoid soy protein isolate?

Ultimately, whether or not you blacklist SPI from your diet depends on your personal needs, body, and goals.

If you have an inflammatory condition or otherwise opt to stay away from GMO's, you probably want to steer clear of SPI. Same goes if you have a sensitive stomach. Valdez says folks with moody digestive systems could experience slight gastric distress from the product.

But if you are on a veggie-forward diet, both experts agree it's probably fine to keep eating SPI. "Soy protein really is the best vegan alternative to whey and casein protein products," says Valdez.

You can always start eating more high-protein, vegan-friendly protein sources too, like pea protein, brown rice protein, and hemp protein. Or re-prioritizing nutrient-dense, whole (as in *not* factory engineered) foods like the 35 high-protein vegan foods on this list.

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Gabrielle Kassel
Gabrielle Kassel is a New York–based fitness and wellness writer. Read more about Gabrielle
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