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You Ask, I Answer: Soy Protein Isolate

Is soy protein isolate a bad form of protein?  Why?

– Kelsey Lepp
(Location Unknown)

Few foods are as polarizing — and misunderstood — as soy.

On the one hand, foods that contain at least 6.25 grams of soy, less than 3 grams of fat, less than 1 gram of saturated fat, and less than 20 milligrams of cholesterol can legally display an FDA-approved statement about soy’s role in helping to lower heart disease risk.

Okay, let’s pause for a second.  That statement perpetuates the inaccurate “low fat = healthy” dogma that to this day has people afraid of consuming heart-healthy foods like nuts, avocados, and coconut.  There are also no limits on how much sugar a product with this statement can have, despite mountains of research showing sugar’s harmful effect on heart health.  Most interestingly, the company that petitioned the FDA for that statement was none other than Protein Technologies International, a company that manufactures — what else — soy protein!

Moving on.  Just as soy has enjoyed plenty of good press, there is also a strong anti-soy movement (some of it led by the National Cattle Association, no less) blaming it for everything from breast cancer to early onsets of puberty to the feminization of men (that last one has more to do with latent mysogyny and silly homophobia than anything else).

In reality, soy supporters and unabashed critics are simultaneously right and wrong.  I have formed my very own soy spectrum.  On the “healthful” side, you have fermented, minimally processed versions (miso, shoyu, tempeh and natto).  Somewhere in the middle you have semi-processed products like soy milk, and way on the other side (the “consume sparingly, if at all” side) lies soy protein isolate.

Let’s start from a very familiar beginning — crop subsidies.  Soy is one of the subsidized crops in the United States, which explains why soy byproducts (from soybean oil to soy flour to soy protein isolate) are so ubiquitous.

Soy protein isolate is a byproduct of soybean oil processing.  To make soy protein isolate, soybeans (practically all the soybeans used to make soy protein are of the Monsanto variety, by the way) are first dehulled, then tempered and crushed to extract oil.  The leftover soy “chunks” (which still contain fiber, water, some fat, and other carbohydrates) then undergo another extraction process that involves hexane — a neurotoxin that is also a substantial component in gasoline.  The next step involves soaking these chunks in a chemical mixture (which commonly contains ammonia and hydrochloric acid) to help concentrate protein levels and achieve a sponge-like texture.  Finally, the mixture is then spray-dried.

By the way — organic soy protein isolate does not utilize hexane in any step of the process.  The folks at The Cornucopia Institute have created this handy list to let you know which protein bars and soy burgers utilize hexane-extracted soy protein isolates (and which don’t).

To give you an idea of the extent of processing, a standard soybean is approximately 40 percent protein, while soy protein isolate is roughly 95 percent protein.

The first red flag: soy protein isolate can only be made in factories.  Whereas you can make almond flour (simply grind almonds in a food processor) or hemp milk at home (blend hemp with water, a pinch of salt, and sweetener of choice and strain through a nut milk bag), soy protein isolate requires hazardous chemicals (hexane is extremely flammable) and temperature extremes unable to be replicated in a kitchen.

While all this processing negatively affects the vitamin, mineral, and flavonoid content of soybeans, it it does not reduce the high level of phytates, which interfere with mineral absorption (fermented sources of soy, like tempeh and natto, have significantly lowers of phytates).  Some research studies have also linked high intakes of soy protein isolate to worsening thyroid function in individuals with already-compromised thyroid glands.

Since soy protein isolate is so inexpensive, avoiding it is not just a matter of not eating vegetarian burgers.  Many cereals, commercial protein bars and shakes, and lower-quality meat products contain soy protein isolate.

No matter what food you’re talking about — whether it’s apples, soy, or corn — the key is to stick with a whole-food, unprocessed (or minimally processed) version.  Biting into an apple, eating tempeh, and nibbling on corn on the cob is infinitely superior to consuming apple juice concentrate, soy protein isolate, and a sugary corn-puff cereal.



  1. Cameo said on April 16th, 2011

    Great info! I get confused every now and again – so it’s nice to be reminded why I avoid soy.

  2. Brandon said on April 18th, 2011

    Why do you put soy milk somewhere in the middle?

  3. Andy Bellatti said on April 22nd, 2011


    Soy milk is not as processed as soy protein isolate (it is mainly whole soybeans with water), but a lot of varieties are made from GMO soybeans and/or have added sugars…. also soy milk does not offer the same healthful properties as tempeh or natto.

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