What Rds Want You to Know *Before* You Sip Soy Protein Isolate for #Gains

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Turn over many a nutrition bar or box of veggie burgers, and you'll often find soy protein isolate (SPI) featured prominently on the ingredient list. But what is soy protein isolate, anyway?

Soy protein isolate is derived from soy meal that's been stripped of its fat and carbohydrate contents, thus leaving behind a concentrated, high-protein byproduct (with more than a 90 percent protein composition). But before you hit "add to cart" with the hopes of a promising, high-protein solution, there are a few things you should know about SPI.

Ahead, we're delving into the nitty-gritty of what soy protein isolate is and how it impacts your body—the good, the bad, and the gassy—according to four registered dietitians.

Experts In This Article

What is soy protein isolate?

According to Lauren Manaker, MS, RDN, LD, CLEC, CPT, a registered dietitian based in Charleston, SPI is a highly-purified form of soy protein. So, what is the difference between soy protein and soy isolate, you may ask? The answer lies in the composition and processing of each:

Soy protein

Some of the benefits of soy include its versatile nutrient composition. "Soy protein refers to the protein that is derived from soybeans, which is a whole food source and includes a variety of nutritional components including fats, fibers, and minerals alongside the protein," Manaker explains.

Soy protein can be found in soybeans themselves, as well as in soy products such as tofu and soy milk, which retain much of the nutritional profile of the original soybean.

What is the difference between soy protein and soy protein isolate?

To reiterate, Manaker says that SPI is produced through a process that removes nearly all the fats and carbohydrates from soy, resulting in a product that's approximately 90 percent protein. "This makes SPI a concentrated source of protein, often favored by individuals looking to increase their protein intake without significantly increasing their intake of fats or carbohydrates," Manaker says.

Soy protein can be found in soybeans themselves, as well as in soy products such as tofu and soy milk, which retain much of the nutritional profile of the original soybean.

On the flip side, however, Manaker points out that this comes with a few drawbacks in terms of nutritional content. "This process of isolation can also strip away some of the other nutritional benefits found in whole soy products, such as fiber and minerals," she says. In turn, the dietitian explains that although SPI can offer several benefits, it may not be appropriate for everyone, but more on that ahead.

What are the potential health benefits of soy protein isolate?

So, is soy protein isolate good for you? According to Manaker, there's a time and place for it. For starters, she explains that it's a great option for those looking to incorporate more protein while sticking to plant-based eating. "SPI is renowned for its plant-based protein content, making it a favored choice among vegetarians, vegans, and individuals seeking to augment their protein intake," she says.

Additionally, Manaker explains that SPI can offer health perks for folks who exercise regularly. "This form of soy protein offers numerous health benefits, including supporting muscle growth and repair, which is particularly beneficial after exercise," she says. Manaker also points out that due to its low-cholesterol composition, it may be a better option for people focusing on heart health or managing cholesterol levels.

7 reasons why you may want to avoid soy protein isolate

Although there are plenty of positive things to say about soy, there here are seven reasons why folks may choose to avoid SPI and other soy-derived products for that matter.

1. Soy protein isolate lacks certain key nutrients

"Soybeans are a great, quality protein because their amino acid content is similar to that in meat, and they're a good source of fiber, minerals, and complex carbs," says Stephanie Middleberg, MS, RD. But to create SPI, soybeans are chemically engineered to "isolate" their protein, and this process strips out all of the other nutrients the original bean contained. "A big issue with soy is that we're eating more of it than ever before and in very processed forms like SPI," Middleberg says. So, although SPI may have started out as a plant, once it gets to you, it's composition has drastically changed.

Manaker echoes this sentiment. "Concerns have been raised about the processing methods used to produce SPI which often involve high temperatures and the use of chemicals, potentially leading to the loss of certain beneficial nutrients and the presence of unwanted residues," she says. "Given these considerations, individuals should weigh the benefits against the potential risks when incorporating SPI into their diet."

While soy protein isolate may have started out as a plant, once it gets to you, it's composition has drastically changed.

2. It may trigger an allergic reaction

Folks with soy allergies should also avoid SPI, as it can potentially trigger allergic reactions ranging from mild to severe, Manaker says. According to Food Allergy Research and Education (FARE), soy allergies are more prevalent among infants and young children—research shows that approximately 0.4 percent of infants in the U.S. have a soy allergy.

Fortunately, most kids tend to outgrow this allergy by the time they reach the age of 10, but it's something to keep an eye on. That said, for folks who are lactose intolerant or have difficulties digesting certain forms of animal protein, soy protein isolate can serve as a gentler, plant-based alternative, Manaker says.

3. GMOs are often involved, if that matters to you

According to the USDA, over 90 percent of the soybeans grown in the U.S. are genetically modified, so most SPI products may come from altered beans. "This means soy protein isolate [can be] chemically modified, processed, and so on," Middleberg says. That said, the FDA clearly states that "GMO foods are carefully studied before they are sold to the public to ensure they are as safe as the foods we currently eat. GMO foods are as healthful and safe to eat as their non-GMO counterparts. Some GMO plants have actually been modified to improve their nutritional value."

4. It can upset your stomach

How digestible is soy protein isolate, exactly? It depends on your gut. Certain food allergies or intolerances can make digesting soy a bit more challenging, says Chrissy Arsenault, MBA, RDN. As such, she recommends starting low and slow when introducing SPI into your daily routine. "Incorporating SPI gradually into the diet in smaller amounts can potentially minimize any digestive side effects."

5. It lacks essential fiber for digestive health

Although SPI may be potentially easier to digest due to its low-fiber content, it can digestion in other ways. "Fiber plays a crucial role in the digestive process, contributing to bowel regularity and the prevention of constipation. The lack of fiber in soy protein isolate means that, while it may be easier to digest for some, it does not offer the same digestive health benefits as whole soy foods rich in fiber," Manaker says.

What can you consume instead of soy protein isolate?

If you choose to avoid SPI, Middleberg says there are tons of options to choose from. This includes suggestions like: natural, whole protein sources like beans, lentils, nuts, and seeds, and organic, non-GMO natural sources of soy like edamame, tofu, and tempeh. To that end, fermented soy sources, like miso, tempeh, and natto have a particular edge. "Fermentation increases the digestibility of soy, adds good bacteria, and reduces the plant estrogen content in soy foods," she adds.

Go ahead, check out the best protein powder options on the market! But also: Try adding a few foods that are rich in plant-based protein, too. Because sticking to whole (rather than... isolated) forms of food is ideal.

A few additional pros and cons about soy:

Well+Good articles reference scientific, reliable, recent, robust studies to back up the information we share. You can trust us along your wellness journey.
  1. Karwowska, Małgorzata, and Anna Kononiuk. “Nitrates/Nitrites in Food-Risk for Nitrosative Stress and Benefits.” Antioxidants (Basel, Switzerland) vol. 9,3 241. 16 Mar. 2020, doi:10.3390/antiox9030241
  2. Křížová, Ludmila et al. “Isoflavones.” Molecules (Basel, Switzerland) vol. 24,6 1076. 19 Mar. 2019, doi:10.3390/molecules24061076
  3. Jargin, Sergei V. “Soy and phytoestrogens: possible side effects.” German medical science : GMS e-journal vol. 12 Doc18. 15 Dec. 2014, doi:10.3205/000203

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