What is Soy Protein Isolate? Is it bad for you?

Most types of protein powder are derived from milk or plant-based foods like soy and pea. Soy protein isolate is increasingly popular among dieters and vegan athletes, packing a hefty nutritional punch. But how does it compare to whey protein?

Current research suggests that whey and soy protein offer similar benefits in terms of mass and strength gains. Soy is an excellent source of isoflavones, iron, copper, and manganese. Whey protein, on the other hand, offers large doses of calcium, phosphorus, zinc, and magnesium. 

The truth is that you don’t need to choose between the two. It’s perfectly fine to use both whey and soy protein isolate as part of a diet plan. Even so, you might be wondering if safe to consume soy — after all, we’ve all heard the rumors about its estrogenic effects. 

There is also some concern about the GMOs in soy. According to the Royal Society and other sources, over 83% of soybean crops are genetically modified. 

That’s what we’re going to discuss today. Our experts will break down the benefits and drawbacks of soy protein isolate, examine its nutrition value, and compare it to other types of protein. 

What Is Soy Protein Isolate? 

Like whey, soy protein comes in different varieties. A popular choice is soy protein isolate, which consists of at least 90% protein. It’s produced by removing carbs, fats, and other non-protein components from defatted soy flour. 

Soy protein isolate can be used for a multitude of purposes. In addition to protein shakes, it’s added to meat and fish products, surimi, cheese dressings, frozen desserts, fruit purees, infant formulas, and more. You can also blend it into smoothies or use it to make your own protein bars. 

This ingredient enhances moisture retention and improves the texture of meat products. As a dietary supplement, it may help fill nutritional gaps and make it easier to increase your protein intake. 

A major advantage is that it contains no lactose or animal-based ingredients, which makes it suitable for vegans and people with dairy allergies or lactose intolerance. But there are some potential drawbacks you should be aware of (more on that later). 

Pure soy protein isolate has little or carbs and fats. However, soy protein powder may contain dextrose, high-fructose corn syrup, fats, and other ingredients that affect its nutritional value. Manufacturers often add fillers to improve its texture and flavor. 

Ideally, choose an organic brand or one that has no sugar and artificial ingredients. If you prefer a slightly sweet version, look or protein powders containing stevia and natural flavors. 

Soy Protein Isolate Nutrition Facts

Quality soy protein isolate has a good nutritional profile and fits into most diets. Depending on the brand, it provides around 96 calories per ounce — that’s about one scoop.

You’ll also get the following nutrients:

• 25.1 grams of protein
• 1 gram of fat
• 50% of the DV of copper (daily value)
• 23% of the DV of iron
• 18% of the DV of phosphorus
• 10% of the DV of zinc
• 4% of the DV of calcium

This type of protein is also rich in B vitamins, such as thiamin, folate, and choline. Like whey, it boasts high doses of amino acids, including leucine, isoleucine, tyrosine, valine, arginine, and others. 

Whey protein isolate, by comparison, has the following nutritional value per ounce:

• 105 calories
• 20.3 grams of protein
• 4.9 grams of carbs
• 6% of the DV of calcium

Some brands of whey protein are carb-free. Others have added sugar. You can also find lactose-free formulas. 

Each serving delivers 110 calories, 24 grams of protein, 2 grams of carbs, and 0.5 grams of fats. It’s also a great source of calcium, potassium, phosphorus, and amino acids. 

However, some folks are allergic to milk or eggs, so their only option is to use beef protein or plant-based protein powders. Soy isn’t a bad choice — just make sure you pick a quality formula. 

Key Nutrients in Soy 

First things first, let’s talk about the nutrients in soy. In addition to protein, this plant-based food contains B vitamins, essential minerals, and antioxidants. 

Copper, one of the most abundant minerals in soy, regulates iron metabolism, energy production, neurotransmission, and other physiologic pathways. It also plays a key role in brain development and immune function, points out the National Institutes of Health (NIH). 

Your bones and muscles store about two-thirds of the copper in your body. Although copper deficiency is rare, it may affect people with Celiac disease, as well as those taking high doses of vitamin C or zinc supplements. 

If left unaddressed, this condition may lead to:

• Anemia
• Thyroid problems
• Fragile bones and osteoporosis
• Weaknesses and fatigue
• Recurring infections
• Memory problems
• Sensitivity to cold 
• Vision loss 

A 2014 case report suggests that copper deficiency may lead to progressive vision loss. This mineral supports the proper functioning of your nervous system. Therefore, low copper levels can affect your nervous system, vision, memory, learning abilities, and motor control. 

Soy Protein as a Source of Iron

Soy protein isolate is also a great source of iron. If you’re a vegan or vegetarian, you may not be getting enough of this mineral in your diet. 

Iron contributes to protein synthesis and hemoglobin production. Hemoglobin helps transfer oxygen from your lungs to muscles and other tissues. 

A diet low in iron can lead to anemia, fatigue, tiredness, shortness of breath, irregular heartbeat, and other issues that affect your health and physical performance. 

Phosphorus, another essential nutrient in soy, supports bone growth and development, cell function, energy production, and nerve signaling. 

This mineral also plays a role in muscle contractions and the production of certain hormones and enzymes. It accounts for about 1% of your body weight, being the second most abundant mineral in your system. 

If your diet is low in phosphorus, you may develop anemia, bone pain, and osteomalacia. Recurring infections, difficulty walking, and muscle weaknesses are all common symptoms of phosphorus deficiency. 

The Truth about Soy Isoflavones

One reason why most guys avoid soy is its high content of isoflavones, a class of phytoestrogens. These compounds have weak estrogen-like effects. 

Soybeans are the primary food source of isoflavones. Other foods, such as peanuts, beans, and chickpeas, contain these polyphenols too, but in smaller amounts. 

According to a study published in the Journal of the American Oil Chemists’ Society, soy protein isolate only retains 26% of the total isoflavones in soy flour. These natural compounds are lost during washing, extraction, and other processes. 

What this means is that soy protein isolate is lower in isoflavones than soybeans and other soy products. 

These naturally occurring compounds should not be equated with the hormone estrogen, states a 2016 review featured in Nutrients. 

Unlike estrogen, they don’t increase the levels of C-reactive protein, an inflammatory marker. Additionally, isoflavones don’t affect the thyroid gland, breasts, or uterus, whereas excess estrogen does. 

The Linus Pauling Institute says that soy isoflavones may improve blood lipids and vascular function, relieve menopause symptoms, and protect against some types of cancer. More studies are needed to confirm these findings.

Effects of Soy Protein Isolate on Athletic Performance 

Now that you know more about soy protein isolate, you may be wondering how it affects sports performance. Is it just as good as whey? Does it help with muscle and strength gains? 

The short answer is yes. Most studies confirm its beneficial effects on hypertrophy, post-workout recovery, and overall performance. But there are some drawbacks you should consider. 

First, let’s focus on the positive. 

Soy protein isolate may help reduce exercise-induced muscle damage and speed up recovery in athletes. Furthermore, it may decrease inflammation and oxidative stress, leading to a lower risk of muscle injury during exercise. 

This dietary supplement may help increase lean mass and strength when used as part of a training program. At the same time, it may reduce fatigue and cause positive changes in hemoglobin and calcium levels. 

Like whey, soy is a complete protein, meaning that it contains all of the essential amino acids required for optimal health and performance. Additionally, it’s easy to digest and break down. 

Some studies indicate that soy protein might be just as effective as whey for strength athletes. Note, though, that it’s lower in leucine than milk proteins. This amino acid increases protein synthesis, making it easier to build mass and recover from training. 

Despite these benefits, there is an ongoing debate as to whether or not athletes should incorporate soy into their diets. This brings us to the next point…

Soy Protein Isolate: Risks and Caveats

As mentioned earlier, most soy crops in the U.S. are genetically modified. The long-term effects of GMOs on human health are not known. Sure, you can buy organic soy protein, but be prepared to pay extra. 

Next, consider the biological value (BV) of soy, which is much lower than that of casein, beef, or whey protein. Soy protein has a BV of 74. Let’s see how it compared to other protein sources:

• Whey protein: 104
• Egg: 100
• Milk: 91
• Beef: 80
• Casein: 76

Biological value is a measurement that shows how much of the protein in food can be used for protein synthesis. 

Generally, proteins with a high BV score increase IGF-1 and nitrogen retention to a greater extent than low BV proteins. Additionally, they are more effective at reducing muscle loss due to their high anti-catabolic activity. Whey, eggs, and milk proteins are superior to soy in this regard. 

Vintage Brawn

Our signature formula used in Vintage Brawn™ boasts a combination of slow- and fast-digesting proteins from milk, beef, and egg whites. 

Another drawback of soy protein is its high content of anti-nutrients. 

Like most legumes, soy contains protease inhibitors and lectins. These compounds interfere with the absorption of iron, zinc, calcium, and other minerals, which may result in nutrient deficiencies. 

According to Harvard Health, lectins may also affect the gut flora and immune function, leading to inflammatory diseases. Their risks outweigh any potential benefits. 

But that’s not all. The protease inhibitors in soy disrupt the activity of chymotrypsin and trypsin, two enzymes that help your body absorb and digest protein. 

Soy isoflavones may cause issues too, notes a research paper published in Nutrients. These compounds may increase the number of proliferative cells in tumors and raise cancer risk. In the long run, they may suppress immune function and promote the growth of breast cancer cells.  

Is Soy Protein Isolate Bad for You?

Without a doubt, soy protein is one of the most controversial sports supplements on the market. Some athletes swear by it for optimal performance and better health. Others say that it can mess up your hormones and hamper your gains. 

The truth is somewhere in the middle. Since most studies are conflicting, it’s to draw a definite conclusion. A quality brand of soy protein isolate is unlikely to cause any harm when used in moderation. 

Whey protein delivers more nutrients than soy and has none of its potential drawbacks. But it’s not a good fit for vegans and individuals with lactose intolerance or dairy allergies. If you fall into any of these categories, it makes sense to reach for plant-based proteins. 

Beware that soy may interfere with certain medications, such as birth control pills, tamoxifen, and warfarin. Also, it may not be safe for those with liver or kidney diseases, rhabdomyolysis, goiter, and other conditions. 

Luckily, this isn’t your only option as there are plenty of other vegan protein sources, like pea, rice, or hemp protein powder. 

What’s your take on soy protein isolate? Have you ever used it? Drop a few lines below and share your experience!