The English word "protein" actually originates from a Greek word - proteios - that means "prime" or "primary". They couldn't have picked a better word considering how fundamentally important protein is for humans. After all, protein is present in every cell of the body!
When protein comes to mind, we instantly think about building muscle mass and shaping our physique. But are there other reasons why we need to eat enough protein, that go beyond muscles? After all, it's a macronutrient so we know it's essential. So, what exactly is protein's job in the body?
Roles of Protein
• Helps grow, maintain and repair body tissues, including muscles (of course, we knew that), tendons, blood vessels, skin, hair, and nails.
• Structural proteins, such as collagen, keratin, and elastin provide support for the body. Collagen, the most abundant protein in your body, provides structure to bones, tendons, ligaments, and skin.
• Contractile proteins (such as actin and myosin) assist with muscle movement and contraction
• Creating and maintaining enzymes, including digestive enzymes essential for us to extract nutrients from our food
• Creating and maintaining hormones, such as insulin
• Creating and maintaining antibodies, thereby supporting immune function
• Creating and maintaining neurotransmitters, such as dopamine and serotonin
• Transport proteins can act much like a bus or train, transporting essential molecules to other parts of the body. For example, hemoglobin transports oxygen throughout the body.
• Replace worn out cells (protein turnover). When it comes to muscles, this is important to help improve muscle quality and replace old muscle with well-functioning muscle.
• Amino acids are used to create
- glutathione, a powerful antioxidant
- creatine
- nitric oxide (NO) gas. Arginine is one of the amino acids use to create this. Nitric oxide is an important gas released by the walls of arteries to help regulate blood flow, blood pressure, and blood fluidity. It helps prevent blood clots, thickening of artery walls, and inflammation in the arteries that can lead to hardened walls. Clearly, NO is important for heart health.
- RNA and DNA
• The amino acids glutamine, glutamate, and aspartate are used as fuel by the small intestine
• The amino acid glutamine provides energy for lymphocytes and macrophages, key immune system fighters (Immune system cells need food, too!)
• Large amounts of amino acids are used by the mammary glands to help produce breast milk during lactation.
• Proteins help cells "communicate" with each other. In order for the body to initiate any of its normal processes or responses, the cells need to know what is going on in other parts of the body. Some proteins will act as receptors on cells. A "signaling" molecule will bind to the protein receptor to communicate a "message" or start a process. A classic example of this is insuln binding to an insulin receptor on a cell to communicate to the cell that it's time to clean up and remove blood from the blood stream.
• Increases the thermic effect of food. What does this mean? Well, when we eat, our bodies work hard to process that food - digestion, absorption, storage, oxidation ALL require energy. Yes, your body burns stored energy and your metabolism goes up when this happens. It turns out that, compared to carbs and fat, protein can have as much as three times more thermic effect. That means, the body has to work harder and burn more to process proteins, compared to fats and carbs.
• Help your body maintain a normal pH level.
Hopefully this can help increase your appreciation of protein and how essential it is that we consume adequate amounts for our body type, age, and activity level. In fact, see our next article to learn about how protein needs change as we age.
References
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Rezaei, R., Wu, Z., Hou, Y. et al. Amino acids and mammary gland development: nutritional implications for milk production and neonatal growth. J Animal Sci Biotechnol 7, 20 (2016). https://doi.org/10.1186/s40104-016-0078-8
P. Li, Y. L. Yin, D. F. Li, S. W. Kim and G. Wu, Br. J. Nutr.,2007, 98, 237–252
Karst H, Steiniger J, Noack R, Steglich HD: Diet-induced thermogenesis in man: thermic effects of single proteins, carbohydrates and fats depending on their energy amount. Ann Nutr Metab 28:245–252, 1984
Westerterp KR, Wilson SA, Rolland V: Diet induced thermogenesis measured over 24h in a respiration chamber: effect of diet composition. Int J Obes Relat Metab Disord 23:287–292, 1999
Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000. Section 22.3, Collagen: The Fibrous Proteins of the Matrix. Available from: https://www.ncbi.nlm.nih.gov/books/NBK21582/
Hamm, L. L., Nakhoul, N., & Hering-Smith, K. S. (2015). Acid-Base Homeostasis. Clinical journal of the American Society of Nephrology : CJASN, 10(12), 2232–2242. https://doi.org/10.2215/CJN.07400715