Protein is composed of amino acids, and different amino acids can have drastically different properties. For example, leucine is an essential amino acid in the class of branched chain amino acids (BCAAs); it initiates a strong anabolic response. On the other hand, glycine is an amino acid that can be synthesized in the body and, while it is useful in the generation of collagen (connective tissue), it plays only a minor role in muscle protein synthesis. Proteins also differ in the rate at which they are digested and therefore, 1) the rate at which they can deliver amino acids to the blood stream and 2) their ability to decrease appetite. Norton et al. (2012) demonstrated that the leucine content of a meal may be one of the most important factors for postprandial muscle protein synthesis. Therefore, protein sources that are rich in leucine, such as whey, will lead to stronger anabolic responses (gram for gram).
Thus, the type of protein you select for your meals and supplements can be important. The table below outlines the key differences in protein types and when it is best to consume each.
| ||Complete?* ||Leucine content ||Rate of digestion (relative) ||Effect on satiety (fullness, relative) ||Good for post-workout? ||Good for bedtime? ||Notes |
|Milk ||Yes ||10% ||Mid ||Mid ||Yes ||Ok ||80% casein, 20% whey |
|Whey ||Yes ||11% ||Fastest ||High ||Yes-best ||Ok || |
|Casein ||Yes ||8% ||Slow ||Low ||Ok, but not the best ||Yes-best || |
|Soy protein isolate ||Yes ||8% ||Fast ||Low ||Yes ||Ok || |
|Egg white ||Yes ||9% ||Mid ||Mid-high ||Yes ||Ok || |
|Chicken breast ||Yes ||7.5% ||Varies ||High ||Yes ||Ok ||Properties vary depending on the method of preparation |
|Collagen ||No ||3% ||Slow ||High ||Ok, but not the best ||Ok ||Often incomplete digestion |
*A complete source of protein contains adequate amounts of all 9 essential amino acids.
How protein can be processed into different forms
Protein Concentrate: Other components are removed from the food matrix to concentrate the protein. The concentrate is typically 40-90% protein. For example, milk protein concentrate is produced by removing most of the fat, sugar, water, and minerals from milk to form a concentrated source of milk protein (whey and casein). Forms of concentrated proteins that are available include soy, whey, rice, egg, and milk.
Protein Isolate: When a protein is isolated to it’s almost pure form, it is called protein isolate. Protein isolates contain the highest percentage of protein possible and are free of fat and carbohydrates. This type of protein is often more expensive than the concentrated form. Whey and soy proteins are available as protein isolates.
Hydrolyzed Protein: The protein strand is broken down into smaller poly-peptides to accelerate absorption and its ability to stimulate post-workout anabolic processes. The process maintains the amino acid composition, but it makes the protein taste very bitter. Hydrolyzed forms of protein that are available include whey, soy, wheat, and collagen.