The Importance of Proteins

What are proteins?

Proteins are an essential macronutrient for everyone, not just athletes. Proteins are large molecules made up of amino acids which are composed of hydrogen, carbon, oxygen, and nitrogen. Protein is one of the three main macronutrients your body needs in order to function. Just like carbohydrates, protein provides four calories per gram, while fats provide nine calories per gram. However, protein is not utilized as an energy source unless you are in a catabolic state (2).

Amino Acids

In order to build proteins, peptide bonds link amino acids. The side chains of the amino acids determine what the protein will be. There are 20 amino acids that form together to make up different proteins. There are nine essential amino acids and 11 nonessential amino acids. Essential amino acids are ones that must be consumed through one’s diet, while nonessential amino acids can be synthesized by the body. The nine essential amino acids include isoleucine, leucine, histidine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. The nonessential amino acids include alanine, glycine, proline, tyrosine, aspartic acid, glutamic acid, arginine, serine, cysteine, and asparagine (1). There are also conditionally essential amino acids. These amino acids cannot be synthesized by the body due to an illness or lack of necessary precursors. For example, individuals with the disease phenylketonuria (PKU) have a mutation with the enzyme phenylalanine hydroxylase, which usually plays a part in the formation of tyrosine (1).

Why is protein important?

Proteins are involved in most of the body’s functions and life processes. Amino acids build proteins for new tissue, replace worn out cells, and respond to injury by clotting the blood. They also make hormones, such as insulin and glucagon, which are messenger molecules. They transport lipids, vitamins, minerals and oxygen around the body through active transportation. Additionally, they help to maintain the fluid and electrolyte balance by regulating the quantity of fluids in the compartments of the body. Lastly, when you consume an adequate amount of protein, the body experiences a positive nitrogen balance, which is the optimal state for muscle growth and workout recovery (3).

Providing energy

When you do not consume enough carbohydrates, your body will utilize protein for energy via gluconeogenesis. When the amino acids are degraded for energy, the nitrogen containing amine groups are either dropped and utilized elsewhere in the body or excreted through urea. While carbohydrates are stored as glycogen and fats are stored in triglycerides, proteins do not have a specialized storage. Therefore, in cases of starvation or an extreme caloric deficit, there is a loss of lean muscle mass (4).

Where can you find protein?

Complete proteins provide all nine essential amino acids (1). These can be found in foods such as meat, eggs, poultry, fish, and dairy. Incomplete proteins do not provide all nine essential amino acids and must be combined with another food group for protein complementation.

Edited by PreRd intern, Lauren Gatto

Written by Emily Smith: Hi, my name is Emily Smith. I am currently an undergraduate Dietetics student at Auburn University and will pursue my Master's degree in Nutrition & Dietetics while completing my DI internship. I am a competitive bodybuilder, therefore I have an extreme passion for sports nutrition. As an RD, I plan to combine my passion for both nutrition and exercise.

References:

1. https://med.libretexts.org/Bookshelves/Nutrition/Book%3A_Intermediate_Nutrition_(Lindshield)/02%3A_Macronutrient_Structures/2.02%3A_Proteins/2.2E%3A_Types_of_Amino_Acids

2. Gurina, Tatyana S. “Biochemistry, Protein Catabolism.” StatPearls [Internet]., U.S. National Library of Medicine, 2 Mar. 2020, www.ncbi.nlm.nih.gov/books/NBK556047/. 

3. Mori, Hiroyasu. “Effect of Timing of Protein and Carbohydrate Intake after Resistance Exercise on Nitrogen Balance in Trained and Untrained Young Men.” Journal of Physiological Anthropology, BioMed Central, 6 Aug. 2014, www.ncbi.nlm.nih.gov/pmc/articles/PMC4155766/#:~:text=When%20protein%20synthesis%20exceeds%20protein,growth%20%5B1%2C2%5D.&text=Because%20muscle%20protein%20synthesis%20peaks,accumulation%20%5B5%2D7%5D. 

4. Schiaffino S;Dyar KA;Ciciliot S;Blaauw B;Sandri M; Mechanisms Regulating Skeletal Muscle Growth and Atrophy. pubmed.ncbi.nlm.nih.gov/23517348/.

5. Photo source: https://www.vixendaily.com/diet/best-high-protein-foods-for-weight-loss/