The 4 Biggest Soy Myths: Is Soy Protein Isolate Safe?


Depending on whom you ask, soy is either a superfood which is rich in protein and other nutrients, or it is dangerous substance which will destroy your healthy. With so much conflicting information, what are you supposed to think about soy? To help clear the air, here are some of the most popular myths and misconceptions about soy and the truth behind them.


Myth: Soy contains isoflavones which can disrupt hormones

This is the claim about soy which incites the most fear, especially in men. Anti-soy advocates say that the isoflavones in soy, chemicals which are similar to estrogen, will cause estrogen-like effects and reduce testosterone levels. The fear mongers can often be heard saying that soy will cause testicular shrinkage, lower sperm counts, and, if given to infant boys, can disrupt development.

The soy isoflavones can have an effect on estrogen receptors, which is why soy is commonly recommended for treating symptoms of menopause. But here is where the anti-soy advocates get it wrong. They neglect to mention that there is more than one type of estrogen receptor in the body. Soy does not have any effect on the estrogen receptors which would cause problems like smaller testicles or reducing testosterone levels (source).

In a meta analysis of 50 treatment groups, researchers found that soy did not cause reduced testosterone levels. No study has ever found that soy causes reduced fertility, even when soy is given to infants (source). However, soy is associated with numerous benefits for men. An analysis of 14 studies found that soy reduces the risk of prostate cancer.  Want to learn more?  Read this article about scientifically-proven reasons vegetarians make better lovers.

Myth: Soy causes breast cancer

This myth is also linked to concerns about soy isoflavones. Because soy acts on some estrogen receptors, people assumed that it would have the same effect as estrogen supplements (which does increase risk of breast cancer). But no study has ever found a positive link between breast cancer and soy isoflavones. In fact, it is the opposite which is true. Soy isoflavones may reduce the risk of breast cancer because they help regulate cell growth by blocking negative effects of natural estrogen. One study even found that soy reduced the likelihood of breast cancer reoccurring in women (source).

Myth: Soy depletes nutrients from the body

It is easy to understand where this myth comes from because soy does contain antinutrients. An antinutrient is basically anything which blocks nutrients from being absorbed. In the case with soy, the antinutrients are natural chemicals called phytates. Because phytates bind to certain minerals, they can prevent some iron, zinc, and calcium from being absorbed. The keyword to note here is “some”.   You will still absorb a considerable amount of those nutrients, even with the phytic acid. The phytic acid in soy will in no way deplete nutrients from your body.

It is important to note that soy is very high in all of these nutrients which is supposedly blocks. So, while you might not be actually absorbing all 6.8mg of iron found in a cup of soy beans, you are still getting a lot of iron.

For people who are really worried about getting the most nutrients from their food, there are a few tricks for reducing phytates. Cooking and fermentation reduces phytates in soy. You can also add a splash of vinegar to soy beans while they are soaking to kill the phytates (source).

To learn more about antinutrients, read this article about the bioavailability of iron and this article about calcium bioavailability.


Myth: Soy prevents heart disease

Soy is considered to be a heart-healthy food. It is high in fiber, which can help reduce cholesterol. Soy also helps promote production of the natural chemical nitric oxide. Nitric oxide dilates blood vessels, which can reduce blood pressure. However, just adding soy to your diet isn’t going to prevent or treat heart disease. Unless you are also eating a healthy, well-balanced diet which is low in saturated fats, then the soy isn’t going to do you much good.  If obesity is causing your heart problems, learn more about the vegan diet for weight loss here.

Is Soy Protein Isolate Safe?

If you read food labels, then you have definitely seen the ingredient “soy protein isolate” listed in packaged foods.  Soy protein isolate is found in foods like veggie burgers, soups, power bars, breakfast cereals and much more.  Since soy is a superfood, you might think that isolated soya is good for you – right?  But soy isolate is anything but healthy and may be downright dangerous. The reason has to do with how soy protein isolate is made.

How Is It Made?

By definition, soy protein isolate is at least 90% protein from soy beans.  Did you ever stop and think how they separate the protein out from the beans to make isolate?

As described in this report in the journal Nutrition and a report by Cornucopia, most soy proteins are made from a process which involves hexane extraction.  The soy beans are soaked in a “hexane bath.”  The hexane causes the fats to separate out of the beans.  This same process is often used for extracting oils from seeds, such as when making canola oil.  More on hexane use in cooking oils here.

Next, the defatted soy is soaked in ethanol or acidic waters to remove carbohydrates and flavor compounds.  The result is a substance which is 90+% protein and can be added to foods to boost the protein content.

Not all soy isolates are made with hexane.  It is also possible to make soy isolate by using machines which squeeze the oil out of the soy. Another method of making soy isolate involves using water to separate the oils.  (Source) However, the hexane method is most commonly used because it is cheap and fast.  Before you worry about the health risks of soy foods, know that foods made with whole soy – such as tofu and tempeh – don’t use hexane.  The entire soy bean is made to make the food.

What is Hexane?

Hexane is a petroleum byproduct of gasoline refining.  Because it has a boiling point of 50 to 70 degrees F, hexane can be used as an easily-evaporated solvent.  In addition to extracting oils from soy beans, hexanes are also used in cleaning agents (degreasers) and also as a solvent for glues, inks, and varnishes.

The Soy Foods Organization of America (SANA) says that hexane has been used in food production for over 70 years with no reports of side effects.  However, this PubChem report says that hexane import and export was negligible up until the 1980s.  The 2002 production range was over 1 billion pounds of hexane.  Clearly hexane use is on the rise.  It may be too early to tell if hexane is causing health problems.

Health Risks of Hexane

There is a long list of health risks associated with hexane.  The CDC has classified hexane as a neurotoxin.  The UN’s GHS system lists many potential risks, including these:

  • H304: May be fatal if swallowed and enters airways [Danger Aspiration hazard – Category 1]
  • H315: Causes skin irritation [Warning Skin corrosion/irritation – Category 2]
  • H336: May cause drowsiness or dizziness [Warning Specific target organ toxicity, single exposure; Narcotic effects – Category 3]
  • H361: Suspected of damaging fertility or the unborn child [Warning Reproductive toxicity – Category 2]
  • H372: Causes damage to organs through prolonged or repeated exposure [Danger Specific target organ toxicity, repeated exposure – Category 1]

Despite all of these health risks of hexane, the FDA does not currently have a limit to how much hexane residue is allowed in soy foods.  However, they do have a limit of 5 ppm (parts per million) for fish protein isolate.  In the European Union, there is an upper limit of 30 ppm in defatted soya.  In the Cornucopia study, the researchers tested soy meal to see how much hexane reside was present.  They found that 21ppm of hexane residue!  According to Slate, later studies found levels of hexane as high as 50 ppm.

How to Avoid Hexane in Soy

The easiest way to avoid hexane is to avoid eating processed foods altogether.  But I get how hard that can be.  As bad as processed foods are, they also make our lives a lot easier and it’s nice to have a veggie burger as a fallback dinner plan.

The other way of avoiding hexane is to buy organic foods. Hexane is forbidden in organic foods.  Some brands have also committed to using hexane-free soy only in their foods, such as the brand Amy’s Kitchen.  Cornucopia has a list of brands which are free of hexane-extracted soy protein.


The fact that hexane is classified as a neurotoxin and associated with numerous health risks makes it a bit scary to eat soy protein isolate.   What will happen if all that hexane residue gets into our bodies?

The truth is that we don’t really know how safe hexane-extracted soy protein isolate is.  The CDC has set limits on hexane, but these limits are for hexane in the air.  The idea is that hexane floating around in oil-extraction factories is dangerous for workers who might breathe it in.

Yes, breathing in hexane particles is probably going to be a lot worse than digesting small amounts of residue.  And I have yet to find any study which looks at the health effects of consuming hexane.  However, it isn’t encouraging that pretty much all of the studies which have found negative health effects of eating soy foods were done using soy isolates (more on whether soy is good or bad for you here).

Considering that hexane in soy protein isolate could be dangerous, it seems wise to avoid it completely.

Just in case you aren’t convinced, remember that soy protein isolate is used in processed foods which probably also contain added sugars, hydrogenated oils, additives, and fillers.  For your health (not to mention your wallet), you should avoid processed foods as much as possible.

Image credit:Edamame by Wesley Chan.  (

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Diane Vukovic

Diane Vukovic is a vegan mom, health nut, and kitchen diva. When she's not deducing veggie nutritional facts, she's probably dancing crazily with her daughter or traveling somewhere in Europe.