Protein Supplements, Nutrition, Reviews, Side Effects & More

Protein powder
In a 12-week clinical trial, men who supplemented with protein powder after resistance training experienced an average of 47% gains in strength across all major muscle groups.

What is Protein – Definition

By simple definition, proteins are linear polymers composed of multiple amino acids. With 20 different types of amino acids, thousands of possible combinations can link together to form long chains which remain held together by peptide bonds.3

Proteins are dynamic and complex macromolecules that are a critical energy source and building block for the human body. At the cellular level, protein is responsible for the regulation, structure and function of the body’s organs and tissues.1

Protein Synthesis and Muscle Building: The Function of Proteins

Proteins play a role in almost all human functions and are essential to the compositions of muscles, bones and skin.1,4,5 Each human has several hundred thousands of different proteins in their body at any given time.4

Protein Synthesis

Protein synthesis, or translation is a process which occurs in the cytoplasm and converts nucleic acids into entirely new proteins.18 As a complex mechanism, ribosomes support the translation of protein-coded genes in mRNA into protein. The cell organelles help combine amino acids into polypeptide chains, which after several modifications turn into functioning protein for the body to use.3, 18

In order to maintain muscle mass, a balance between muscle protein synthesis (MPS) and muscle protein breakdown (MPB) must occur in the body. This is known as a nitrogen, or protein balance.6

By consuming adequate amounts of energy, especially carbohydrates, athletes can achieve a nitrogen balance, which is the optimal state to build muscle and maintain weight. If appropriate amounts of energy are not available, important amino acids used for protein synthesis become oxidized instead to help sustain energy levels.11

Adding protein to your diet can ensure valuable amino acids can go through protein synthesis and support sustained lean muscle mass.22

Function of Proteins

Proteins can be found in a variety of different forms throughout the human body, but are commonly classified by their function and shape. Proteins can be fibrous, globular or membrane protein.1,3

Each classification of protein has a unique function to perform within the body.5 Proteins may work as antibodies, enzymes, cellular messengers, assist in transportation, storage, muscle contraction and structural composition.1, 4, 5

Examples of Proteins

In the antibody function, protein binds to foreign entities such as bacteria or viruses to defend the body.1 Working within the immune system, the specialized proteins move throughout the body to immobilize antigens until an accumulation of white blood cells can destroy the invader.3

As an enzyme, protein contributes to chemical reactions that occur in the cell and help read genetic information stored in DNA to produce new molecules. An example of proteins working as an enzyme can be found in the food digestion process. Protein is present in the stomach, small intestine and saliva to assists in breaking down food.1,4

Examples of Proteins – Growth Hormone
Growth Hormone, a cellular messenger protein, regulates body composition, muscle growth and fat metabolism.

Receptor and cellular messenger proteins, such as growth hormones send biological alerts throughout the body to coordinate complex processes between various tissues, cells and organs.1 Located around the outside of cells, messages can be transmitted internal or externally.4

In a transportation or storage role, protein binds to various molecules or atoms and help circulate or store them throughout the body.1 Ferritin, a storage protein, helps accumulate iron in hemoglobin.1, 5

Protein plays a crucial role in both the structural composition of muscles and their ability to contract. From walking to blinking, muscle proteins such as actin enable the body to move. Additionally, these proteins structurally support cells throughout the body.1,4

Protein Structure

The basic structure of protein is composed of one or more chain structures known as Amino Acids. There are 20 different types of amino acids that can be connected together in large chains. How the amino acids connect together determines the structure and function of the protein.1 Typically, proteins will consist of anywhere from 50 to 2,000 amino acids linked together.4

Protein Deficiency

According to the World Health Organization, protein deficiency can lead to a loss of muscle mass, growth issues, and weakening of the heart, immunity and respiratory systems.8,9 Protein deficiencies are commonly associated with diets lacking nutrient-rich foods over. This is due to the fact that many important macronutrients and vitamins are often naturally found in combination with protein. Inadequate levels of protein challenge the body’s ability to repair muscles, increase muscle mass or perform essential human functions.8

Special populations, particularly the elderly and children are most at risk to adverse reactions from a protein deficiency. The elderly population requires one of the highest protein:energy ratios across all societal groups. Protein deficiency can lead to poor bone health, and a lack of protein can contribute to a multitude of serious health outcomes or diseases.8

Dietary Requirements & Protein Intake

How much protein do you need
The recommended daily protein intake, in ounces.

Daily protein intake, as recommended by the Institute of Medicine, should be a minimum of 0.8 grams of protein for each kilogram of body weight, for individuals 18 years or older. In terms of total energy, 10-35% of daily calories should come from protein sources.9,11 It’s important to note, that the Recommended Daily Allowance (RDA), is the minimum required for body the function properly and avoid illness.11

For endurance and strength athletes, how many grams of protein a day will increase due to raised energy requirements. Recent studies show that both endurance strength training athletes experience higher levels of protein oxidation and require additional protein to maintain a nitrogen balance in the body.11

Sources of Protein

Protein can be produced within the body, or by consuming and modifying amino acids found in our food.9 There are two different types of amino acids; essential and nonessential.9

Essential amino acids are only found animal protein sources and cannot be made in the body. Nonessential amino acids still play a vital role, but can be synthesized within the body. Food sources such as fruit or vegetables are not considered essential amino acids because they are missing one or more of the required amino acids.9

Good sources of nutritional protein include skinless poultry, lean beef, soy proteins, legumes, fish, nuts and low-fat dairy products.13,14 Additionally, protein supplements can be added to your diet to reach the RDA and diversify your sources of protein.

Protein Calculator

Developed by the National Academy of Science’s Institute of Medicine, the interactive Daily Reference Intake (DRI) calculator (no follow) helps individuals and healthcare professionals evaluate daily calorie and macronutrient needs tailored to a patients’ height, weight, age and activity level.12

While various protein calculators are available online, the DRI is updated to reflect the most recent scientific findings on daily requirements. For added convenience, the DRI is now also available as an app that can be downloaded through the Apple Store or Google Play.

How much protein should I eat?

In the United States, the RDA of protein is 56 grams/ day for adult males and 46 grams/ day for females.9

Several studies on nitrogen balance conclude that endurance athletes may require up to two times the protein requirements than stated by the RDA to support nitrogen balance, optimized recovery and muscle building.6, 11, 19 It’s suggested that protein turnover may become more efficient in endurance athletes over time and that 1.2 to 1.4 grams per kilogram a day will help maintain balance.11

Athletes focusing on strength and resistance training may require 1.2 to 1.7 grams of protein per day total, significantly higher than the 0.8 grams/kg RDA guideline. Additional amino acids, protein and energy are all needed to promote muscle growth, particularly in the early stages of training where increase in muscle mass is usually most significant. 11

Protein Supplements – Classifications

Recent studies indicate that the use of high-quality proteins such as whey, casein or soy are effective for the repair, synthesis and maintenance of skeletal muscles when taken after training.11

Supplementing with protein, particularly after resistance training helps to promote fullness, retention of lean mass, and may be used a strategy for weight loss or maintenance.15, 22 Interestingly, not all proteins suppress hunger or promote muscle growth in the same way. This is caused by the quality, the quantity and nutritional composition of the protein supplement.22

After consulting leading-edge clinic research, Supplement Analyst has broken down each category of protein powder below to bring you the latest on all things protein and help you choose the right protein for your lifestyle.

Whey Protein

Whey protein powder is the most common protein powder available on the market, and the most extensively researched. Derived from cow’s milk, whey is considered the ‘fast-acting’ protein due to the fact that it can absorbed quicker than casein protein.34

When compared against soy and casein protein in clinical trials, whey protein stimulated more muscle protein synthesis (MPS) both after resistance training and during resting periods.33 Whey protein is particularly rich in leucine, a branched chain amino acid that is considered to play an important role in signaling protein synthesis.37

Post-exercise levels of leucine and branch chain amino acids, observed significantly higher in whey protein supplement group, out performing Soy by more than 2 times. High levels of leucine found in whey protein have been positively correlated with lean body mass responses.

Whey protein proven to increase essential amino acids and branched chain amino acids.
Post-exercise levels of leucine and branch chain amino acids, observed significantly higher in whey protein supplement group, out performing Soy by more than 2 times. High levels of leucine found in whey protein have been positively correlated with lean body mass responses.

In a 2013, researchers examined effects of supplementing with whey protein in regards to the development of lean body mass. Subjects were divided into three control groups and took either a whey protein, soy protein or isocaloric supplement containing carbohydrates. After nine months, subjects were tested for post-exercise plasma levels of branched chain amino acids, essential amino acids and leucine; three markers that contribute to muscle protein synthesis and potentially leaner muscle mass. The data observed showed significantly higher gains in lean body mass in the whey group, followed by the carbohydrate group, then soy.37

Additional studies have noted that ingesting whey protein rather than carbohydrates or soy proteins over long periods of time resulted in increased muscle hypertrophy. 6

Further, in a study conducted on the role of whey protein induced satiety, researchers observed that pre meal appetite was more suppressed in subjects who had taken a whey protein preload, compared to any other tested proteins. 6

As the most widely available and often economical choice, whey protein is great option for athletes who don’t have any dietary restrictions or intolerances and are looking to promote muscle growth.

Click here for Supplement Analyst’s Official Whey Protein Reviews.

Whey Protein Isolate

Whey protein isolate is a more concentrated form of protein which has had other macronutrients eliminated or reduced.31

Whey protein isolate powders usually contain 92% protein compared to most whey proteins which hover around 80%. This means an increase in grams of protein per serving and often significantly less calories, fat, carbohydrates, lactose and cholesterol.30 Like whey protein, whey protein isolate is fast digesting to help deliver protein when you need it.

According to a study conducted in 2014, a diet supplemented with whey protein isolate significantly increased levels of essential amino acids and leucine, when compared to a control and placebo group. Both markers are critical to building and maintaining muscle mass.31

Casein Protein

Casein is the second milk-based protein often used in protein supplements. Known for its slow release of protein, casein releases amino acids into the bloodstream and may deliver sustained protein over time.34 Although whey and casein are both derived from cow’s milk, they contain very different amino acid profiles. Casein contains glutamine, an amino acid particularly needed when the body is under stress. Casein also works to inhibit the unwanted breakdown of protein.34

Thinking of purchasing a casein supplement? Read our Casein Protein Reviews first. (jump to reviews)

Benefits of Protein Supplements

Thinking of buying a Protein Supplement? Click here for the latest buying guide.

Emerging scientific evidence points to diets in high in protein contribute to overall good health.6,15,23 Weight loss studies have proposed that a high protein diet (25-30% of energy from protein) shows significant progress in terms of body composition and metabolic profile, suggesting the important role of protein on weight loss and sustaining lean muscle.6, 23

Protein has the highest rating of satiety or feelings of fullness among macronutrients compared to carbohydrates or fats. Clinical research indicates that increased satiety has been noted when meals contain 25-81% protein.15, 21 In a 2004, randomized parallel design trial, researchers compared a 20% protein intake compared to 15%. Subjects that followed a high protein diet demonstrated a lower percentage of overall body fat, 50% less weight gain and maintained satiety.6,24

Ingesting 20-30 grams of total protein, or 10 grams of essential amino acids immediately after physical activity provides the body with essential amino acids to promote muscle mass and repair muscle tissue.11 Further, ingesting protein is critical for muscle protein synthesis.6

Side Effects of Protein Supplements

While many high-quality protein supplements can promote muscle growth, recovery and assist with weight maintenance;15 supplements can affect individuals differently.

A study conducted in 2002, noted that high protein diets can pose potential side effects such as increased acid loads, particularly as phosphates and sulfates, on individuals with kidney issues or chronic kidney disease.15, 16

To mitigate increased acid levels in the body, try to balance a high protein diet with alkali fruits and vegetables such as bananas, which are high in potassium.15

Long term ingestion of amino acids containing sulphur may also have an indirect effect on blood pressure and renal function in subjects that are obese, have type 2 diabetes, or metabolic syndrome.6

Consuming protein powder when energy demands are minimal, i.e., consuming protein powder without any physical activity, may result in excess protein being converted into glucose and create an energy surplus.15 This could lead to a weight increase if protein supplements are consumed to an excess without any exertion.

Protein Shakes & Powder: The Many Forms of Protein Supplementation

As one of the most popular types of supplements, protein powder comes in a large selection of ingredients, flavors, forms and prices. Widely available in general supermarkets or supplement retailers, protein supplements are often organized by format, such as protein powder, protein bars or ready to drink protein beverages. For the most in-depth reviews on today’s leading protein supplements, read our product reviews (jump to reviews) below.

Protein Powder

Easily found in store or online, the most popular way to integrate protein supplements into your workout routine is by consuming protein powder. For simple consumption, users can mix protein powder with water, low-fat milk or milk alternatives to create a convenient protein shake. For added nutritional value, protein powder can be added to fruit and vegetable smoothies.

Prices for protein powder will vary depending how many servings the product contains, grams of protein in the supplement, if it’s widely distributed or if it appeals to specialized markets (aspartame-free, organic, etc.).

When purchasing protein supplements, shopping at a nutritional supplement store or online will offer greater variety, but occasionally higher prices. At a reputable retailer like GNC, protein powder can range from $24.99 to $139.99, which is largely dependent on brand name and weight of the product.

If the brand offers individual servings or a trial offer, it may be a viable option to ensure the flavor, format and price point is right for your lifestyle.

Click here for Supplement Analyst’s latest Protein Powder Reviews.

Protein Bars

Widely available in supermarkets and health supplement stores, protein bars offer an effortless and portable source of protein. With a large selection of flavors, users can find protein bars to suit any taste.

The cost per container of protein bar supplements can range anywhere from $12-$40 depending on how many bars are included, amount of protein (snack vs. meal replacement) or if it adheres to any dietary needs (gluten-free, lactose-free). With this variety, cost ranges from $1- $3.30 per bar, making it a more expensive way to get your protein in. It’s important to consult the nutritional information on protein bars, as some products may be high in other macronutrients or contain large amounts of sugar per serving.

Ready to Drink Protein Shakes

Pre mixed protein drinks offer users a hassle-free way to get protein into their diet. For athletes on the go, or for users who want to sample a brand, ready to drink protein shakes may be the way to go. Similar to protein bars, this no-fuss protein is often sold together in a box of 12, which range from $24.99 all the way up to $67.99. Broken down, that’s $2.08 – $5.66 per bottle, coming in as the most expensive but convenient protein supplement.

It’s important to note that currently, ready to drink protein shakes don’t offer a large variety of products for athletes with dietary restrictions, particularly for lactose-free users, as ready-made drinks often contain milk. However, the supplement industry is constantly adapting and could feature more options soon.

High Protein Foods: Nutritional Protein

A high protein diet filled with nutrient-rich food and snacks can help promote weight loss, retention of lean mass, sustained satiety and overall good health.6,15

When adding foods high in protein to your diet, it’s important to consider the entire protein package, or the additional macronutrients or vitamins they contain.9,15 Many protein-rich animal sources, such as red meats also contain high levels of cholesterol or saturated fats. Processed meats often come with large amounts of sodium and artificial additives.15

Good sources of high protein foods include:

  • Lean protein such as low-fat cuts of sirloin, ground beef that is a minimum of 90% lean, chicken or turkey (without skin)14
  • Seafood that is high in omega 3- fats, such as salmon or trout14
  • Legumes like lentils, chickpeas, beans and dried peas13
  • Processed soy products such as tofu or tempeh13
  • Eggs13,14
  • Low-fat yogurt or milk14
  • Seeds, nuts and nut butters13,14
  • Whole Grains: Kamut, Wheat Berries, Quinoa, Oatmeal13
  • Vegetables: Peas, artichoke and spinach13

Pro Tip: Including a variety of sources is the most effective option for receiving health benefits. Nuts such as peanuts or almonds and Omega-3 fats can both lower the risk of heart disease. Protein in eggs and lean meat are also a good source of iron.17

Vegan Protein Powder and Vegetarian Protein

With an increasing number of individuals choosing to go vegetarian or vegan, a growing amount of animal-free protein supplements are being introduced into the supplement industry.

Vegetarian protein is any protein source that’s not animal-based. For vegetarians, sources such as chicken or beef would be excluded. Vegans however, don’t consume animals or animal by-products such as milk, cheese, eggs or honey. In terms of protein supplements, vegan athletes rely on protein found from plant, hemp or soy sources.

Vegan Protein Powder

While the RDA recommends that individuals consume 0.36 grams of protein per pound, protein requirements for vegan athletes can range from 0.36 up to 0.86 grams of protein per pound.10, 11 This can be attributed to the proteins and amino acids found in plant sources, which are broken down differently than animal sources. According to Reed Mangels, PhD, RD,

“Vegan athletes, especially in the early stages of training, may have higher protein needs than vegans who exercise moderately or who are not active.” 10

Vegan protein sources such as legumes, tofu, veggie burgers, meatless ‘meat’, faux chicken strips or hot dogs are commonly available in supermarkets today. While these products are effective in providing protein, they often take time to prepare and come with increased amounts of artificial additives and sodium.13

While at first this may appear to limit protein sources, recent demand for vegan protein has created a variety of options available. Continue reading below to find out the benefits of hemp, plant-based and soy protein supplements.

Hemp Protein

Gaining popularity over recent years, hemp protein has been perceived to be a heart healthy alternative to traditional protein supplements. Hemp contains high amounts of fiber compared to other protein supplements and an amino acid known as arginine, an important precursor to nitric oxide. 27,28 Derived from hempseed, hemp protein contains no intoxicating properties. Research is still ongoing on the benefits of hemp, compared to other protein supplements or dietary sources. 28

Plant Based Protein

To date, few clinical trials have evaluated the efficacy of plant based proteins aside from soy. In 2015, a clinical trial compared the muscle protein synthesis (MPS) in subjects after ingesting either plant based protein or animal based protein. The consumption of soy protein was observed to have lower rates of MPS when compared to animal sources, and theoretically would need to be consumed in higher doses to reach similar effects. Researchers speculated this may be due to how the protein is broken down and differences in absorption. 29

Soy Protein

As a bioactive plant, soy contains a combination of protein and isoflavones that may benefit overall health. 25 Often found in tofu, or ‘meatless meat’, soy protein supplements are the most commonly studied vegan protein supplement.

In 2011, a randomized controlled trial evaluated the impacts of adding soy protein to the diet of middle aged men (50-65 years) who were moderately overweight and untrained. 22 After the 12-week intervention (combined with resistance training), subjects who took the soy protein noticed increases in strength measurements, lean body mass and decreased waist circumference. 22

Additionally, in a cross-sectional study of postmenopausal woman those who consumed a diet rich in soy protein had a lower waist circumference and body mass index (BMI) compared to those who didn’t consume soy. 25

Pea Protein Powder

Derived from the protein-rich vegetable, pea protein is filled with amino acids and commonly found in vegetarian or vegan protein food or drinks. 26

In a 2008 study, researchers evaluated the efficacy of whey protein, pea protein hydrolysate and a control milk protein for suppressing hunger and the release of satiety hormones. The results indicated the mix of pea protein was the most powerful in controlling appetite and maintaining fullness, as assessed by patients’ ratings. 15, 20

When tested for possible toxicity, data suggested that pea protein isolate did not result in toxic effects and may act as a possible alternative for individuals that are lactose intolerant, or have existing chronic diseases.26


The protein supplement industry is a multibillion-dollar industry with an increasing amount of health products available every year. Recently, a limited amount of supplement companies have been accused of overstating label claims, particularly around the amount of protein available in protein powders and weight gainers.35

Due to the rising cost of raw materials such as whey, unethical supplement companies began protein spiking, or adding filler products to maintain product weight, keeping production costs low and remaining competitive.35

To determine the amount of protein in a product, the nitrogen content is calculated. Manufacturers that have added cheap amino acid fillers into the formula are aiming to inflate the nitrogen content of the product when it’s tested. This results in the product appearing better in terms of protein quality and content even though the increased nitrogen content does not benefit the athlete in the same way.35

This less-than-best-business-practice led to false claims on nutrition labels, spurring class-action cases and lawsuits across the United States. While claims are still being settled, reputable manufacturers and retailers, such as GNC, have gone out of their way to publicly put down the practice, adhere to third party testing or improve labels and marketing.35

Protein Reviews

Click here for the most comprehensive protein supplement reviews.


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