Protein – Introduction

Protein is an essential macronutrient for building skeletal muscle among a myriad of other vital functions, including but not limited to neurotransmission, energy production, cardiovascular function, and immune system regulation.[1] Protein is also used to maintain fluid balance and transport nutrients in and out of cells.

Amino acids are the building blocks of protein and can be combined in various ways to form different proteins in the body. One of the primary uses of amino acids in the body is to synthesise structural proteins such as muscle, skin, and hair. Amino acids are also involved in the synthesis of peptide hormones such as growth hormone (GH), insulin-like growth factor 1 (IGF-1), and insulin.[2]

Protein is available from both animal and plant sources.  Animal sources are considered ‘complete’ proteins (i.e. containing all nine essential amino acids), whereas vegetable sources generally lack one or more of the essential amino acids.[3]

Strength/power athletes generally require 1.5-2.0g/kg/day of protein.[4] Endurance athletes may also require a greater protein consumption. Rather than increasing muscle size and strength, the aim for these athletes is to maintain muscle mass. Studies have shown that the general protein requirement for endurance athletes is 1.2-1.4g/kg/day.[5]

The timing of protein consumption and what sources are consumed are also of importance. Not all proteins are the same, some have advantages over others, particularly at certain times. Certain combinations may also have advantages. Read on to learn more about specific types of protein and the pros/cons of each.

Top Protein Types

Animal-Derived Proteins

Whey Protein

Whey is a complete source of protein and is highly bioavailable in humans (meaning it’s easily digested and utilised). Whey is readily soluble in liquid environments and over varying pH ranges, and is denatured (unfolded) when treated with high heat.[6] Note that denaturing protein doesn’t cause it to lose its nutritional value, but it may cause it to lose some of its biological properties (such as enhancing the immune system or promoting increase of certain growth factors).

Whey refers to the milk serum by-product produced during the curdling of milk and comprises roughly 20% of the protein content in dairy milk, with the rest being casein proteins.[7]  

Whey protein contains a large proportion of the amino acid L-leucine; L-leucine has been found to be a key substrate for stimulating the Mammalian target of rapamycin (mTOR) pathway which regulates muscle protein synthesis (MPS).[8] Research corroborates that the proportion of leucine in a given protein source has implications on the peak MPS rate attained post-ingestion.[9]

Whey protein comes in various forms, such as concentrate, isolate and hydrolysate. Both isolate and hydrolysate forms of whey are >90% protein content with minimal lactose and virtually no fat, but generally lack the immune-enhancing properties that concentrate have.[10] Whey protein concentrate is roughly 70%-80% protein content with small amounts of lactose and fat and thus generally has a creamier, sweeter texture.[7]

Due to its quick absorption, all forms of whey protein are ideal to take right after a workout or whenever a fast acting intake or protein is warranted.

Casein Protein

Casein is the dominant type of protein in dairy milk, comprising roughly 80% of the total. [7]  Casein comes in various forms, including calcium caseinate, sodium caseinate, and micellar casein.[11] Casein is used primarily as an anti-catabolic agent since it is absorbed more slowly and can provide a sustained release of amino acids into the bloodstream over a longer period of time than most other protein.

This longer digestion stems from the way casein forms a gel in the stomach and allows amino acids to be slowly dissipated in the body over the long run. Micellar casein is a soluble, high-quality milk protein powder with a clean flavour. In nature, most casein protein exists as what’s known as a casein micelle. A casein micelle is a colloidal particle that biologically serves to transport insoluble calcium-phosphate complexes in liquid form to the stomach for clotting and subsequent digestion. In fact, over 90% of the calcium content in skim milk is linked with the casein micelle.

Calcium caseinate and sodium caseinate are salt forms of casein protein that are generally inferior to micellar casein in terms of overall quality and bioavailability.

Beef Protein

Beef protein is a complete protein source that has a high biological value. It is also gluten, lactose and soy free, making it a superb hypoallergenic protein source. Most beef protein powders are processed to be low in fat, cholesterol, lactose and other carbohydrates. They may also contain small amounts of creatine, a well-researched performance-enhancing ingredient.

A recent study has shown that consumption of two servings of beef protein isolate or whey protein isolate resulted in significant gains in lean body mass over time, which outpaced gains from resistance training alone.[12]

Egg Protein

Egg protein is an extremely low in fat and complete protein source. Supplemental egg white protein is typically sold as a spray dried powder, or in liquid, pasteurised form.[13] Egg white supplementation is a simple and convenient way to add extra protein. The average egg contains about 6.3 grams of protein, 3.6 of which come from the egg white.[14] Egg protein is generally a good alternative to whey and casein for those with dairy allergies.

In addition to protein, other key nutrients found in the egg white are riboflavin, niacin, folate, vitamin B12, calcium, iron, copper, zinc and sodium. Egg protein is a great adjunct when stacked with weight gaining supplements or whey protein powder for post workout nutrition.

Plant Proteins

Soy protein isolate, hemp protein, and brown rice protein are all plant-based protein powders. These are useful for vegetarians or people who have allergies to dairy and egg proteins.

Soy Protein

Soy protein is isolated from soybean, and unlike most plant-based proteins, it is a complete protein. The soybean is a legume originating from eastern Asia that contains no cholesterol and is naturally low in saturated fats. Soy protein is extremely heat stable and is readily soluble in warm water. Due to its neutral taste and physical properties it may be used as a replacement or additive in a variety of food products.

Soy isolates are the most refined soy protein product containing the greatest concentration of protein (90% protein).3 Soy protein is a good source of protein for vegetarians. Soy has been shown to reduce cholesterol, improve cardiovascular health and possibly increase thyroid output. More recent studies have shown that soy protein intake can increase antioxidant levels and reduce oxidation of LDL-cholesterol.[15]

There has been concern among males that the small amounts of phytoestrogens contained in soy protein could boost oestrogen levels.[16] However, research has shown that daily supplementation of soy, whey or soy plus whey does not negatively affect testosterone or inhibit lean body mass changes in males engaged in a resistance exercise program.[17]

Hemp Protein

Hemp seeds are nutritious and contain roughly 35% protein and 47% essential fatty acids (such as omega-3s and omega-6s). Hemp protein is a complete protein source that is also high in fibre to support proper digestive health.[18] The hemp protein sold in food stores is derived from the seed cake left over after pressing the oil.

Hemp protein is high in chlorophyll and other nutrients associated with the seeds including vitamin E, magnesium and zinc. Hemp protein is not highly processed or refined, so it has a rather gritty texture and grassy taste.

Brown Rice Protein

Brown rice protein is a great hypoallergenic alternative to soy protein. Rice protein is not a complete protein due to insufficient levels of the amino acids lysine (recognised for its role in muscle building) and threonine. Though, these amino acids are often added to rice protein products. Rice protein does also have higher levels of the amino acid arginine compared with other protein sources. Arginine is a vasodilator that can enhance blood flow to tissues.[19]

A recent study showed that the effects of rice protein supplementation are similar to whey protein supplementation. Specifically, the study showed that 48g supplementation of rice protein isolate or whey protein isolate, taken post-resistance exercise, improved lean body composition (fat-free body mass) and exercise performance (strength and power); there were no differences between the two experimental groups (rice and whey protein isolate).[20] Rice protein supplements therefore seem effective when compared to whey, as long as you consume them in a high enough quantity.

Protein Blends

Don’t want to go through the hassle of finding different types of protein for different times of the day? Then a protein matrix/blend is a good option. Recent research suggests that combining whey and casein protein is better for muscle growth, and including soy and egg protein can be beneficial.[21], [22], [23]

Common protein types used in blends include:

Whey protein isolate (WPI): Contains a high percentage of protein (>90%) and is virtually lactose, fat and cholesterol free.[10] WPI contains a high concentration of branched chain amino acids and has a high biological value, which is a measure of the proportion of absorbed protein from a food which becomes incorporated into the proteins of the body.

Whey protein concentrate (WPC): WPC has a high biological value, but contains more fat and lactose than WPI.  It has a protein content of 70%-80% and is also rich in branched chain amino acids.[10] Compared to whey isolates, whey concentrate typically contains more biologically active components.

Casein protein: Casein is a slowly-absorbed protein source that provides a sustained release of amino acids into the bloodstream over a longer period of time. Casein is used before bed to help limit possible muscle breakdown, as well as increase protein synthesis. The major advantage of blending whey and casein is that it will repair your muscles long after whey has been absorbed.

Egg protein: Eggs have traditionally been used as the standard of comparison for measuring protein quality because of their essential amino acid profile and high digestibility.[24] Egg whites contain all nine essential amino acids. In addition to proteins, other nutrients found in the egg white are riboflavin, niacin, folate, vitamin B12, calcium, iron, copper, zinc and sodium.

Soy protein: Soy protein is isolated from soybean. The soybean is a legume that contains no cholesterol and is naturally low in saturated fats and contains all nine essential amino acids. Soy isolates are the most refined soy protein product, containing the greatest concentration of protein (90% protein).[3] Soy protein is a good source of protein for vegetarians.

Protein Bars

Protein bars usually contain protein, carbohydrates, fat, vitamins and minerals, and additional functional ingredients. Some bars may have only one protein source, such as whey or soy protein isolate, but it is better to get a protein blend to utilise all the functional benefits of different proteins and help support lean muscle mass. Protein bars inevitably contain carbohydrates as well.

Typically, the main sources are sugar alcohols like sorbitol and maltitol, especially in “low-carbohydrate” bars. Protein bars may also contain a blend of vitamins and minerals to support overall health and many chemical processes in the body.

High-protein with moderate to high carbohydrate bars are best suited for athletes looking to get quality protein and carbohydrates for increased energy. They are helpful after a workout to enhance recovery and recuperation and boost carbohydrate storage (glycogen) in muscle tissue.

Low-carbohydrate/high-protein bars are good for people looking to maintain lean muscle mass and lose body fat as part of a diet and training program.

Ready-To-Drink Protein

Fulfilling your protein requirements in a busy life can be difficult. Ready to drink protein (RTD) provides a convenient way to meet your protein requirements on the go. The nutritional value of RTDs, however, is not as good as powders due to the process used to make them stable in liquid form over time.[11]


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[18] Tang, C. H., Ten, Z., Wang, X. S., & Yang, X. Q. (2006). Physicochemical and functional properties of hemp (Cannabis sativa L.) protein isolate. Journal of agricultural and food chemistry, 54(23), 8945-8950.
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