Soy Protein Isolate: Nutrition, Side Effects & How It Compares To Other Proteins

Here, nutrition experts weigh in on the pros and cons of soy protein isolate, its potential side effects, and how it stacks up against other protein sources.

"Soy protein isolate can be found in protein powders, shakes, and bars. In addition, it could also be used in emulsifiers and thickeners, as well as meat alternatives," Vuu adds.

"Soy protein isolate has a PDCAAS score of one, which is considered a high-quality protein source, similar to animal proteins," explains Vuu. This makes it a good choice for supporting muscle growth and maintenance.

Vuu adds, "By removing most indigestible fibers and carbohydrates from the entire soybean, it makes the product more digestible and less likely to cause gastrointestinal problems. This could be particularly useful for people with pancreatic insufficiency or people who have problems digesting complex protein sources."

"Soy protein and soy foods are generally good for the heart and blood vessels because they provide polyunsaturated fat, fiber, vitamins, and minerals, and are low in saturated fat," says Kimberly Gomer, M.S., R.D., LDN, a registered dietitian and nutritionist at Body Beautiful Miami. She points to research that found that swapping red meat8 for plant proteins including soy was associated with a 14% lower risk of heart disease.

As a high-quality protein source, soy isolate can also help combat age-related muscle loss when paired with resistance training.

Specifically, residues of the toxic chemical glyphosate have been found on soybean crops, according to one study10. Additionally, increased pesticide use on soybean crops can cause environmental issues.

In addition, some research12 suggests potential health benefits of soy, such as reducing cancer risk, alleviating menopausal symptoms, and improving memory.

"Other downsides for soy protein isolate may include the large scale of soybean farming, which is often times a form of monoculture. These practices lead to soil degradation, increase susceptibility to pests and disease, and can cause a loss of biodiversity. In addition, soybean farming has also led to deforestation in some areas," warns Vuu.

"Soy protein isolate is a protein that's been isolated from soybeans via chemical engineering," says Gomer. "The soybeans are washed with an acid and then neutralized in an alkaline solution." This high level of processing can affect soy isolate's protein quality14 as well as strip the crop of other healthy nutrients.

As leading amino acid researcher Don Layman, Ph.D., explained on the mindbodygreen podcast, most plant proteins, including soy isolate, are also inherently lower than animal proteins in certain key amino acids like leucine. This means that you have to consume more of them in order to meet your protein targets, increasing your overall calorie intake. While not necessarily a bad thing, this can be a concern for those who are consuming protein to help them lose weight.

For those hoping to take a more whole-foods approach to meeting daily protein needs, here are several less-processed soy products that can be included in a healthy diet:

Ultimately, the choice between soy protein isolate and whey protein depends on your dietary needs, allergies, sensitivities, and taste preferences. Both types of protein can be part of a healthy, balanced diet, states Vuu.

What about soy protein isolate side effects? While soy protein isolate is generally safe for most people when consumed in moderation, there are some potential dangers:

Soybeans are among the eight major food allergens, according to the Food and Drug Administration15. As a result, some people may experience common soy allergic reactions16, such as skin rashes, hives, abdominal pain, vomiting, and diarrhea—even with a soy protein isolate powder.

Some may experience gastrointestinal (GI) distress like bloating or gas after taking soy protein isolate. "Many people have allergies to soy products, and it might be a cause for G.I. distress in some people," explains Vuu.

Consuming large amounts of any type of protein is taxing on the liver and kidneys, and it may be damaging for those with existing liver or kidney disease. However, taking soy protein isolate in moderation as part of a healthy, balanced diet is unlikely to cause any issues.

However, we recommend choosing whole food sources of soy protein or soy protein concentrate over soy protein isolate powders when possible since they're less processed and more nutritious. Other vegan protein powders, like pea protein powder, can also help plant-based eaters meet their daily protein needs.