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Soy Protein vs Whey Protein - What's Best For Your Goals?

Reading Time: 7 minutes 30 seconds


DATE: 2023-02-10

Protein is a critical nutrient for the human body. A certain level of protein intake is needed to create new enzymes, build and repair muscle tissue, and create hormones. Protein is found in every single cell within the human body. It is found in large quantities in our bones, skin, muscles, cartilage, and blood.

Protein is made up of amino acids. These amino acids are linked together to form long chains. Amino acids are building blocks. The body rearranges them to create new protein structures needed to perform specific functions within the body.

For those performing resistance exercise, protein becomes even more important. Protein is critical for muscle building and restoration. One way to ensure adequate protein consumption is by using protein powders and protein shakes. The question then becomes which form of protein powder to use.

There are many varieties of protein powders available. Each offers benefits and drawbacks. Two of the most common are soy protein and whey protein. Debate continues between soy and whey protein and which one is best for use before, during, and after resistance training.

How is Soy Protein Made?

Soy protein is a plant protein. Soy is a type of legume high in protein. To create this plant-based protein, soybeans are ground into a meal. This meal contains no hulls or fat. The soybean meal is then processed into soy isolate. This isolate contains 90-95% protein. Soy protein is naturally low in carbohydrates. Therefore, it is often mixed with additional nutrients to improve taste, texture, and nutritional value.

Soy protein isolate is a common ingredient in many processed foods and dietary supplements, and is often used as a meat substitute or protein supplement for vegetarians and vegans. Soy protein isolate is a complete protein, containing all of the essential amino acids the body needs to function properly. Soy protein isolate is also low in fat and cholesterol-free, making it a healthy option for some people. 

How is Whey Protein Made?

Whey protein is made from cow's milk. First, the milk is pasteurized to kill any bacteria. Then special enzymes are added to separate the casein—milk solids used to make cheese—from the whey. The whey is then further processed to remove carbs, fats, and excess water. What remains is whey concentrate. This is the least processed form of whey protein. Further processing will result in whey isolate and whey hydro-isolates.

Whey protein isolate is made by removing the majority of the non-protein components such as fats and carbohydrates from whey, which is the liquid part of milk that separates during the production of cheese. Similar to soy protein isolate, this process results in a powder that is 90-95% protein (by weight). Whey protein isolate also is a complete protein, containing all of the essential amino acids the body needs to function properly. It is high in branched chain amino acids (BCAAs) which are important for muscle growth and recovery.

Whey protein isolate is commonly used by athletes and bodybuilders as a dietary supplement to increase muscle mass and improve exercise performance. It is also used for weight loss, as it is a low-calorie, high-protein option. It can be consumed as a shake or added to food and drinks. It is also used as an ingredient in many processed foods and dietary supplements.

It is important to note that whey protein isolate is derived from milk and if you are lactose intolerant or allergic to milk should avoid it. Also, consuming large amounts of whey protein isolate may have negative effects on health, so it is important to consume it in moderation.

Soy Protein and Whey Protein: Amino Acid Profiles

Amino acids are the building blocks of proteins. There are 22 different amino acids used by the body. The nine amino acids listed below are essential. This means they cannot be synthesized by the body. Essential amino acids must be obtained through dietary protein sources.

  1. Histidine

  2. Isoleucine

  3. Leucine

  4. Lysine

  5. Methionine

  6. Phenylalanine

  7. Threonine

  8. Tryptophan

  9. Valine

Soy and whey protein are both a complete protein source. This means that they contain all nine essential amino acids. However, their amino acid profiles do differ in their makeup of both non-essential and essential amino acids.

Soy Protein Amino Acid Profile

Soy protein stacks up well as a balanced protein source. It offers a unique amino acid profile. Soy protein contains a substantial amount of branched chain amino acids. These BCAAs can be used and readily converted for energy production. Soy protein is high in arginine, phenylamine, and tryptophan.

  • Arginine is an important amino acid in the body. It is often found at active sites in proteins and enzymes. It promotes cardiovascular health, combats fatigue, and stimulates the immune system.

  • Phenylamine is an essential amino acid. It is used by the body to produce proteins and other important molecules.

  • Tryptophan is another essential amino acid. It is important to support normal growth. It also supports the production and maintenance of proteins, muscles, enzymes, and neurotransmitters.

Whey Protein Amino Acid Profile

Whey protein contains the highest percentage of essential amino acids. Whey protein is high in leucine, isoleucine, methionine, and lysine.

  • Leucine is a BCAA critical for protein synthesis and muscle repair. In addition, it helps regulate blood sugar levels and stimulates healing the production of growth hormones.

  • Isoleucine is another BCAA. Isoleucine is involved in muscle metabolism and is heavily concentrated within muscle tissue. It is also important for immune function, energy regulation, and hemoglobin production.

  • Methionine plays a critical role in metabolism and healthy tissue growth. It also aids in the absorption of zinc and selenium, crucial vitamins to support overall health.

  • Lysine plays a major role in protein synthesis. In addition, it is critical for hormone and enzyme production, calcium absorption, and energy production.

Building Muscle with Soy and Whey Protein

Utilizing a combination of soy and whey protein powders at separate times can maximize their effectiveness and support.

Soy Protein Benefits

Soy protein has less potential for producing ammonia. Ammonia is a primary cause of muscle fatigue. Because of this, soy protein is best used before and during exercise. Soy protein also contains phytochemicals. Phytochemicals are believed to support cardiovascular health and aid prevention of osteoporosis.

When digested, soy protein promotes muscle synthesis at a high rate. It provides a high concentration of BCAAs, which the body readily converts for energy production. Soy protein does help build muscle mass. But it may not be the most effective protein choice. Soy protein sits somewhere in the middle of the pack as far as muscle protein synthesis goes. A 2009 study showed soy to be inferior to whey protein in synthesizing protein for muscle mass gains. Soy may be of most benefit when taken in combination with other proteins such as rice protein, pea protein, or hemp protein.

Soy Protein Potential Drawbacks

While soy protein offers many benefits, there are some noted concerns.

  • Soy protein contains phytates. Phytates are also known as antinutrients. These antinutrients are known to reduce the availability of iron and zinc. However, phytates should not adversely affect your health unless you consume a very imbalanced diet, relying only on soy food as a source for iron and zinc.

  • There is additional concern that soy may affect thyroid function. Isoflavones in soy can disrupt the production of thyroid hormones and interfere with iodine uptake in the thyroid gland. However, studies have shown soy to have a very mild effect on thyroid function.

  • Some consumers steer clear of soy protein due to its phytoestrogen content, such as soy isoflavones. Phytoestrogens are chemical compounds that exert estrogen-like properties. Phytoestrogens bind to estrogen receptors in the body. These phytoestrogens may disrupt natural hormone levels in the body.

Whey Protein Benefits

Whey protein supplement has the highest biological value (BV) of any protein source. The BV rates the availability of a protein source after ingestion. Whey protein is arguably the most rapidly absorbed protein. This makes it ideal for consumption post-workout. For the past 50 years, whey protein has been viewed as the perfect protein supplement. It may surpass all other protein powders when it comes to muscle building. Whey protein has a relatively fast absorption rate in the body after consumption. It is more readily digested and almost 100% of the whey protein consumed is absorbed.

Whey Protein Potential Drawbacks

Most of the negative side effects of whey protein are related to digestion.

  • The main carb in whey protein is lactose. Individuals who are lactose intolerant do not produce enough lactase. Lactase is the enzyme needed to digest lactose. Whey concentrate is the least processed form of whey and causes the most gastrointestinal (GI) discomfort. For those with lactose intolerance, switching to a whey isolate or whey hydro-isolate may relieve GI symptoms. Isolates and hydro-isolates are more processed and have more lactose removed. This makes them more ideal and appropriate for lactose intolerant individuals.

  • Whey protein is an animal protein that comes from cow's milk. Therefore, individuals with an allergy to cow's milk may also be allergic to whey protein. However, cow milk allergies are very rare in adults. Up to 90% of people with cow milk allergies grow out of them by the age of three.

  • Some individuals report experiencing constipation from taking whey protein powder. However, this is not a normal side effect of whey protein. Some individuals with lactose intolerance may experience constipation due to the slowed movement of the gut.

Other Factors to Consider in the Whey vs Soy Protein Debate

Aside from various health benefits and potential drawbacks, there are a few other factors to consider when choosing between whey and soy protein.

Taste and Texture

Whey protein is known to have a smooth, creamy texture with a mild nutty taste. Soy protein typically has a stronger nutty flavor and a somewhat grainier texture. Both proteins are available in a variety of flavors and formulations. You may try one and find that it has an off-putting chalky texture. Your best shot of finding a protein powder with a taste and texture you love is trial and error.

Dietary Restrictions

Whey protein comes from an animal source. Therefore, it is not an appropriate choice for vegan or vegetarian consumers. Soy is a healthy vegan protein source. In addition, soy does not contain lactose and is therefore a better choice for those with lactose intolerances.

The ketogenic trend continues to captivate consumers. Both protein powders are typically low in carb content and can support a ketogenic diet. As the powders are processed, most of the carbs are stripped. This leaves behind a protein rich powder. However, be mindful of checking nutrition facts on both soy protein powder and whey protein powder. To combat some of the off-putting chalky textures and tastes other ingredients are often added. These ingredients can increase the carb content as well as added sugars. Make sure whether you're buying soy protein or whey protein, you check that label.

In summary, what works for one person, may not work for another. Both soy protein and whey protein carry pros and cons. Both are high in protein quality and have significantly high absorption rates. Both can help increase lean body mass when consumed regularly. It's all about finding which one works best for you and supports your goals. Experiment to find what works best for you, because there truly is no one size fits all.

Interested in learning more about nutrition and how it can support your goals in the gym? Step up your nutrition knowledge with ISSA's Nutrition Certification course.

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