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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:
- 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.
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!
Disclaimer: None of the individuals and/or companies mentioned necessarily endorse Old School Labs or COSIDLA Inc. products or the contents of this article. Any programs provided for illustration purposes only. Always consult with your personal trainer, nutritionist and physician before changing or starting any new exercise, nutrition, or supplementation program.
Is soy protein isolate really bad for you? ›
Soy is a good source of protein, fiber, and an array of important vitamins and minerals. It also contains health-promoting compounds like isoflavones. Though you may have heard concerns about soy's GMO status or phytoestrogen content, most scientific evidence suggests that there's no need to avoid soy products.What is meant by soy protein isolate? ›
A dietary protein isolated from soybeans that contains isoflavone phytoestrogens. Soy protein isolate has been shown to reduce tumor incidence and growth in some animal studies, possibly by modulating estrogen metabolism, reducing tumor cell proliferation, and inducing tumor cell apoptosis.Is soy protein isolate bad for your liver? ›
It has been reported that soy protein intake can reduce serum cholesterol and triglycerides and also reduce accumulation of cholesterol and triglycerides in the liver which can lead to reduction of liver steatosis [8,9,10,11].What is the difference between soy protein and soy protein isolate? ›
Soy protein is a word that could describe anything from soy milk to tofu to miso and beyond; 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 is engineered to create a higher quality of protein.Is soy protein isolate high in estrogen? ›
Soy is unique in that it contains a high concentration of isoflavones, a type of plant estrogen (phytoestrogen) that is similar in function to human estrogen but with much weaker effects. Soy isoflavones can bind to estrogen receptors in the body and cause either weak estrogenic or anti-estrogenic activity.Does soy protein isolate increase estrogen? ›
Soy protein isolate increases urinary estrogens and the ratio of 2:16alpha-hydroxyestrone in men at high risk of prostate cancer.Is isolate protein good or bad? ›
Whey isolate is by far one of the best forms of protein available on the market, and the reason behind it is that they generally lack the fats, carbs, lactose, and cholesterol that are found in many other forms of protein powder.Is isolate protein healthier? ›
Whey isolate undergoes different processing than whey concentrate, which results in the isolate containing more protein with less carbs and fat per serving. However, these nutritional differences are small, and there is not strong support for different effects of these two types of whey protein.Is protein isolate good for you? ›
Whey protein and whey isolate protein can be beneficial in many ways, including: Building muscles. Protein is essential for building strong muscles. Whey protein, in particular, contains types of amino acids that are great for muscles.Is soy protein isolate bad for your kidneys? ›
Using soy protein instead of animal protein reduces development of kidney disease in animals. Reducing protein intake preserves kidney function in persons with early diabetic kidney disease.
Is soy protein isolate bad for thyroid? ›
Hypothyroidism is generally treated with synthetic thyroid hormone — and soy has long been thought to interfere with the body's ability to absorb the medication. However, there's no evidence that people who have hypothyroidism should avoid soy completely.Does soy protein cause inflammation? ›
Soy and its products have been shown to have anti-inflammatory properties, particularly in patients with diabetes mellitus and cardiovascular diseases [12,13,14,15]. Due to the inflammatory nature of UC, consumption of soy products may affect UC disease symptoms as well.What is soy protein isolate made from? ›
Soy protein isolate is a concentrated form of plant-based protein originating from soybeans. Like soy, it contains all nine essential amino acids, though its protein content is significantly higher at about 90 percent protein.Is soy protein isolate hard to digest? ›
It may upset your stomach
Many people have allergies or intolerances that make it hard to digest soy. But even if you're not one of them, soy protein isolate may make your stomach rumble, says Slayton.
Numerous clinical studies have found that daily consumption of up to 50 grams of soy protein is not only safe, but may also be effective in improving risk factors for chronic disease such as some types of cancer, diabetes, and cardiovascular disease.Why avoid soy protein isolate? ›
It contains unhealthy additives. Foodtrainers founder Lauren Slatyon, MS, RD, says that the chemical process used to isolate soy protein often leaves behind substances you don't necessarily want to be eating, like aluminum and hexane. “Think of bathing in toxic bath oil,” Slayton says.Does soy protein isolate increase testosterone? ›
This updated analysis, which included over 40 clinical studies, again found that neither soy nor isoflavones affect total or free testosterone levels.Does soy protein mess with hormones? ›
According to a handful of studies, soy consumption may have a link to raising serum estrogen in humans (3), and potentially causing thyroid disorders (4). Animal studies have also suggested potential male infertility and breast cancer associated with soy consumption.Does soy turn into estrogen in the body? ›
Soy comes from soybeans. It's made of isoflavones, which are a type of plant estrogen. It is structurally different from the estrogen in our bodies, and plant-based estrogen does not convert into the estrogen our bodies make when we eat it.What foods are high in estrogen? ›
- Flaxseeds. Flaxseeds are the richest dietary source of lignans (polyphenols found in plants). ...
- Soy. ...
- Peaches. ...
- Garlic. ...
- Red Wine. ...
- Sesame Seeds. ...
- Cruciferous Vegetables. ...
Is soy protein isolate good for menopause? ›
Soy isoflavones may help reduce hot flashes and night sweats that many women have during menopause. In clinical studies, postmenopausal women who eat high amounts of dietary soy protein (20 to 60 g per day) generally have fewer and less intense hot flashes and night sweats than those who eat less soy.Which brand isolate protein is best? ›
- 25 Best Whey Isolate Protein Powders. Elm & Rye Protein Powder. ...
- Elm & Rye Protein Powder. ...
- 1st Phorm Phormula 1. ...
- Run Supps Isolate Whey Protein. ...
- Cutler Nutrition Total ISO Protein Powder. ...
- Kachava Protein. ...
- Legion Whey Isolate Protein Powder. ...
- 1st Phorm Level-1.
It is safe to drink protein shakes every day, but be sure to obtain the majority of your protein and other foods from whole food sources. Without whole food sources, you'll be missing out on other valuable nutrients that are vital for health and supporting your workout performance and recovery.What is the difference between protein and isolate? ›
The main difference between the two is the amount of protein contained per scoop of protein powder. Isolate protein contains about 90 per cent of protein per scoop and a negligible amount of fat and lactose. On the other hand, protein concentrates contain 25 to 89 per cent protein (depending on the brand you buy).How often should I take isolate protein? ›
A commonly recommended dosage is 1–2 scoops (around 25–50 grams) per day, usually after workouts. It's recommended that you follow the serving instructions on the packaging. Keep in mind that if your protein intake is already high, adding whey protein on top of your current intake may be completely unnecessary.Does isolate protein increase cholesterol? ›
Although it's higher in fat than other types of protein, many studies show that whey protein lowers “bad” cholesterol and increases “good” cholesterol. Whey isolate is easier for some to digest than whey concentrate, but may lack some of the beneficial fat and nutrients of whey concentrate.Does soy protein raise blood pressure? ›
Soya protein consumption significantly reduced SBP and DBP in both hypertensive and normotensive subjects, and the reductions were markedly greater in hypertensive subjects. Significant and greater BP reductions were also observed in trials using carbohydrate, but not milk products, as the control diet.Is soy protein bad for cholesterol? ›
Although eating soy-based foods can slightly reduce your low-density lipoprotein (LDL, or "bad") cholesterol level, the American Heart Association has concluded that soy doesn't significantly lower cholesterol.How does soy protein affect blood pressure? ›
Our results showed that soy consumption significantly improves SBP and DBP. Subgroup analyses identified a greater reduction in blood pressure among younger participants with lower baseline diastolic blood pressure, and in trials lasting for < 16 weeks duration.Does soy isolate decrease testosterone? ›
1. Soy and soy-based products. Some research shows that regularly eating soy products like edamame, tofu, soy milk, and miso may cause a drop in testosterone levels. For example, one study in 35 men found that drinking soy protein isolate for 54 days resulted in decreased testosterone levels ( 3 ).
What foods should thyroid patients avoid? ›
- iodized salt.
- fish and shellfish.
- seaweed or kelp.
- dairy products.
- iodine supplements.
- food products containing red dye.
- egg yolks.
- blackstrap molasses.
So if you do, it's a good idea to limit your intake of Brussels sprouts, cabbage, cauliflower, kale, turnips, and bok choy, because research suggests digesting these vegetables may block the thyroid's ability to utilize iodine, which is essential for normal thyroid function.Who should avoid soy? ›
May affect your thyroid
Soy foods don't affect thyroid function in people with healthy thyroids, found a Loma Linda University review of 14 studies. But, if you have an underactive thyroid you might want to watch how much soy you eat.
Red meat and processed meats, including bacon, hot dogs, lunch meats and cured meats. Refined grains, including white bread, white rice, pasta and breakfast cereals. Snack foods, including chips, cookies, crackers and pastries. Sodas and other sweetened drinks.Can soy protein cause joint pain? ›
While people with inflammation should generally avoid dairy, soy protein products like tofu and tempeh have been found to reduce pain in joints according to a study from Oklahoma State University. An easy way to add soy to your diet is using soy protein powder.Is soy protein isolate a form of MSG? ›
However, MSG occurs naturally in ingredients such as hydrolyzed vegetable protein, autolyzed yeast, hydrolyzed yeast, yeast extract, soy extracts, and protein isolate, as well as in tomatoes and cheeses.Is soy protein isolate better than whey? ›
The latest research says whey protein is a better choice if you want to shed fat, pack on muscle, and boost testosterone. If you want a plant-based alternative, soy protein isn't necessarily a bad choice. In fact, the FDA states that it's better for your heart health than whey.What can I use instead of soy protein isolate? ›
Chickpeas, lentils, lupine, sorghum, broad beans and many other legumes can replace soy in many formulations. Some of these are rich in high-quality protein and fiber and contain low levels of fat compared to soy.How long does it take to digest soy protein isolate? ›
A medium digesting protein is a protein that is typically digested within 3 to 3 ½ hours and includes a number of proteins such as whole egg protein, egg white protein, pea protein and rice/soy protein.Does soy protein isolate cause bloating? ›
Soy is difficult to digest, which can cause gas, bloating and general discomfort.
Is soy protein good for gut health? ›
Recent studies have shown that soy-based foods have a significant positive effect on gut microbiota. One of the handfuls of plant foods to contain all nine essential amino acids, soy-based foods are today gaining popularity - not just for their many health benefits, but also because they positively affect gut health.What foods are high in soy protein? ›
- 3 ounces water-packed tofu — 6 to 13 grams.
- 3 ounces silken tofu — 6 grams.
- 8 ounces plain soy milk — 3 to10 grams.
- 8 ounces Edensoy Extra Plain soy milk — 10 grams.
- 8 ounces vanilla soy milk — 3 to 6 grams.
- 1/4 cup (1 ounce) soy nuts — 12 grams.
- 2 tablespoons soy nut butter — 6 to 8 grams.
Drinking just two cups of soymilk or eating one cup of tofu produces blood levels of isoflavones that can be 500 to 1,000 times higher than typical estrogen levels in women.How much isoflavone is safe? ›
Although diets rich in soy or soy-containing products appear safe and potentially beneficial, the long-term safety of very high supplemental doses of soy isoflavones is not yet known. One study in older men and women found that 100 mg/day of soy isoflavones for six months was well tolerated (154).Is it OK to eat soy protein everyday? ›
The Bottom Line:
Yes, you can go ahead and eat soy daily and feel good about it. Just be sure that you're consuming an appropriate amount—about three servings—of lesser processed soy foods. Some forms of soy like these below are more nutritious than others, so here's a quick rundown.
No. Soy intake does not raise or lower a man's testosterone levels. Derived from soybeans, soy is a high-protein substance found in many foods, such as edamame, tofu, tempeh, miso, soy flour, and soy milk. It can also be found in some supplements.Does soy protein isolate reduce testosterone? ›
Soy Protein Does Not Lower Testosterone or Raise IGF-1 Levels in Men. Research from the University of Illinois by Bosland et al.Who should not eat soy? ›
May affect your thyroid
Soy foods don't affect thyroid function in people with healthy thyroids, found a Loma Linda University review of 14 studies. But, if you have an underactive thyroid you might want to watch how much soy you eat.
Not enough evidence exists to suggest a link between soy consumption and hormone changes in the body such as increased serum estrogen, breast cancer risk, thyroid hormone imbalances, and infertility.Does soy increase testosterone or estrogen? ›
Abstract. Concerns that the phytoestrogens (isoflavones) in soy may feminize men continue to be raised. Several studies and case-reports describing feminizing effects including lowering testosterone levels and raising estrogen levels in men have been published.
What form of protein is best? ›
Whey protein is one of the most commonly used proteins and is best for day-to-day use. It contains all of the essential amino acids and is easily digested. It helps boost energy and can reduce stress levels. Whey isolates and concentrates are best to use after a workout.Is isolate better than protein? ›
The carbohydrate and fat content of whey protein isolate is very low, making isolate the better choice if you want to limit your intake of those nutrients. Both concentrate and isolate help you build muscle and get stronger as part of a protein-rich diet.Which is better protein or isolate? ›
If you have lactose intolerance, whey isolate is a better choice than whey concentrate. Much of the lactose and sugars are removed from whey isolate during processing. But if you have a dairy allergy, both whey and whey isolate may upset your stomach. In that case, look for plant-based protein instead.Is soy protein isolate good for muscle? ›
Unlike most other plant-based proteins, soy protein provides you with enough of all the essential amino acids to support muscle protein synthesis. That means that your body can use soy protein by itself to build muscle to the fullest extent.How much soy does it take to affect testosterone? ›
Soy is completely safe to eat and is not going to have a significant impact on your testosterone levels. As long as you eat the recommended amount of 25 grams of soy a day, you likely won't experience any problems in your sexual health.Can eating too much soy lower testosterone? ›
No. While there are worries that soy may affect testosterone, research has found that soy consumption did not decrease reproductive hormone levels (4).