Soy Protein Isolate: Nutrition, Side Effects & How It Compares To Other Proteins
Next time you are grocery shopping, take a look at the ingredients list of any prepackaged product and you're likely to find soy protein isolate near the top. But what exactly is soy protein isolate? And even more—what's the difference between soy protein and isolate?
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.
What is soy protein isolate?
"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.
Benefits of soy protein isolate:
It's a high-quality source of plant protein.
"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.
It's easy to digest.
Soy protein isolate is easy on your digestive system because it's stripped of most of the indigestible carbohydrates and fibers found in whole soybeans5. This makes sense considering its high PDCAAS score.
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."
It may support heart health.
Several studies6 have indicated that consuming soy protein can boost heart health by helping lower LDL ("bad") cholesterol and triglycerides (blood lipids)—two significant risk factors for cardiovascular disease7.
"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.
It may help prevent bone and muscle loss.
As you age, it becomes increasingly important to maintain bone health. That's because your bones begin to break down more than they replenish as you get older.
Specifically, the research suggests that soy isoflavones can prevent osteoporosis-related bone loss and increase bone mineral density in normal-weight people. Also, they can diminish bone resorption in overweight and obese individuals.
Downsides of soy protein isolate:
Soybeans are associated with high GM and pesticide use.
Over 90% of soybean crops are genetically modified to be herbicide-tolerant, which can lead to increased pesticide use.
Soy contains phytoestrogens that may aggravate existing hormonal issues.
"Soy and soy-related products contain phytoestrogens, which can mimic the hormone estrogen in the human body," explains Vuu. "Many people still debate the effects of phytoestrogens on human health. However, some studies have demonstrated adverse effects on hormonal and reproductive health in sensitive individuals."
Soy monocultures can negatively affect the environment.
"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 isolate is highly processed and refined.
"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.
Soy protein is lower in certain essential amino acids.
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.
Other soy products
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:
- Soy milk (Choose unsweetened and organic)
- Soy protein concentrate
Is soy protein isolate better than whey?
Both soy protein isolate and whey protein are complete protein sources with benefits and drawbacks. Soy protein isolate is plant-based, making it a suitable choice for vegans, vegetarians, and those seeking to reduce their animal consumption. It's also free from lactose and cholesterol and is low in fat. Whey protein is an easy-to-digest high-quality protein that's more rapidly absorbed than soy protein.
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.
Risks and side effects
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:
People with allergies should avoid taking it.
It may cause GI distress.
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.
It may be harmful for those with kidney and liver issues.
Is there a difference between soy protein and soy isolate?
The terms "soy protein" and "soy protein isolate" refer to different forms of soy-derived protein with varying levels of processing and protein content. Soy protein is an all-encompassing term that includes any protein extracted from soybeans, including soy protein concentrate, texture soy protein, and soybean products like tofu, tempeh, edamame, soy curls, and miso.
Soy protein isolate is a more processed form of soy protein made by separating the protein from other nutrients, including fiber, carbohydrates, and fats. This form typically contains at least 90% protein by weight.
"Soy protein is a word that could describe anything from soy milk to tofu to miso and beyond," says Gomer. "It's used broadly to describe food made from soybeans. On the other hand, soy protein isolate is the isolated protein from the soybean that's engineered to create a more highly concentrated form of protein."
Does soy protein isolate increase estrogen?
Soy protein isolate contains compounds called phytoestrogens, specifically isoflavones, which can mimic the hormone estrogen in your body. However, the impact of soy protein isolate on estrogen levels and hormone balance is inconclusive.
"However, for most individuals, moderate consumption of soy protein isolate as part of a balanced diet is unlikely to cause significant hormonal imbalances," says Vuu.
Soy protein isolate is a high-quality, easily digestible plant protein source suitable for any dietary pattern. While soy protein isolate is often portrayed as unhealthy due to its phytoestrogen content, scientific research indicates that these pose risks only for those with existing hormonal 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.
Adam Meyer is a health writer, certified holistic nutritionist, and 100 percent plant-based athlete. He graduated from the NutraPhoria School of Holistic Nutrition in 2019 and has since founded Pillars Nutrition. His work has been featured on EatingWell, Eat This Not That!, The Beet, Verywell Fit, The Healthy, Livestrong, Alive, Best Life and others.
Adam lives in British Columbia, Canada, with his wife, two kids and an Australian shepherd. That's where you can find him running mountain trails, working out in his home gym, or writing in a coffee shop.