Protein is one of the essential macronutrients. While it is widely recognized that protein is needed for energy and muscle building, the myriad roles of protein within our bodies is underappreciated. Second only to water, protein is a major component of our bodies. (1) The word protein comes from the Greek “proteios” which means “first” or “primary” (2)
What Are Proteins?
The Role of Proteins
Proteins made by our bodies have many roles. One key role is that of enzymes. Enzymes are important for much more than digestion. Almost every reaction that occurs in our bodies requires an enzyme. Since enzymes increase reaction rates a millionfold, this means that metabolic reactions would occur a million times slower without enzymes – too slow for life as we know it! Proteins are also important as transport and storage molecules. Many small molecules and ions bind to proteins in order to be transported in the blood. Hemoglobin is a well-known protein found inside red blood cells that helps transport oxygen. Another example is transferrin which helps to transport iron. Myoglobin, a protein related to hemoglobin, is found in skeletal and cardiac muscle cells; its role is to store oxygen. The protein ferritin stores iron in our cells, especially liver cells. Proteins are also important for structural support. The most abundant protein in our body is the fibrous protein collagen which accounts for about 30% of our body protein (5). Collagen is abundant in connective tissue such as bone, cartilage, tendons and ligaments as well as the dermis in the skin. Vitamin C is required for the synthesis of collagen. In fact, many Vitamin C deficiency symptoms are due to a lack of collagen.
Albumin is another vital protein in our bodies. It is the most abundant plasma protein. Not only does albumin help with transporting some substances such as bilirubin, it also plays a role in pH buffering. Albumin’s most important role, however, is to help maintain osmotic pressure. The presence of albumin in blood plasma helps to keep fluid in blood. In the absence of albumin fluid remains in tissues resulting in edema. Since albumin is made by the liver it is not surprising that one of the signs of liver disease is edema. The best known role of protein is to build muscle. Muscle contraction is due to the sliding of two types of protein – actin and myosin, the primary constituents of myofilaments. Other types of movement in the body also involve protein. These include the beating of cilia to sweep away debris in the trachea; the whiplike motion of the sperm tail that allows it to swim; and the separation of chromosomes during mitosis.
Other roles of protein include:
Antibodies — these highly specific proteins are produced by some of our white blood cells and help protect us from invaders.
Hormones — many hormones such as insulin and growth hormone are proteins.
Receptors — in our cell membranes, there are many proteins that act as receptors for neurotransmitters, hormones and more.
Control of gene expression is mediated by proteins. Which genes are expressed within a particular cell is regulated in part by proteins. Furthermore, the information in the gene contains instructions to make a specific protein!
While there are other roles of protein this illustrates its importance. Given the obvious necessity of proteins within our bodies, it is clear that adequate protein intake is vital to our health. It is not clear what the ideal daily protein intake should be but low protein intake has definite adverse affects on our health. Symptoms of protein deficiency include brittle hair and nails, muscle weakness, getting sick often, feeling weak or hungry, mood changes and trouble thinking (6). Edema, anemia and slow growth in children are also signs of protein deficiency (7). Daily protein recommendations are typically 0.8 g/kg of body weight for most adults with active individuals, pregnant women, children and older adults needing a little more. While this may not seem to be a lot of protein, a 2018 study found that more than a third of adults over the age of 51 are not meeting this requirement (8). While it has been found that very high levels of animal protein intake may increase risk of kidney stones in at risk individuals (9, 10), most of us would probably benefit from increased levels of protein intake. Protein needs to be taken in on a daily basis since it is not stored in our bodies. Every time we eat protein, it is broken down to amino acids by our digestive system. These amino acids are absorbed and will fill up the “amino acid pool” that exists in our body fluids. Once that pool is full, any additional amino acids are burned for energy. In fact, the liver obtains a lot of its energy through the catabolism of amino acids.
Benefits of increasing protein intake are many and include helping maintain an ideal body weight. Protein can do this by causing reduced appetite and hunger levels (11) as well as decreased late-night snacking (12). Protein increases the satiety hormones GLP-1, peptide YY and CCK and also decreases the hunger hormone, ghrelin (13). Increased protein intake is important for bone health – a diet deficient in protein increases the risk of osteoporosis. In fact, there is a positive relationship between protein intake and increased bone density (14, 15).
Strength training without adequate protein is not effective at increasing muscle mass. However, training along with increased protein intake does increase muscle mass and strength (16).
As you savour your next protein-rich meal pause to appreciate all the roles that the protein you are eating will play in your body.
IHN students go through a full functional analysis of proteins in our Body Metabolism course; one of the 19 unique courses that make up IHN’s Applied Holistic Nutrition Diploma Program. Want to experience a taste of what this transformative program is all about? Be a student for a day and sit in on a class!
Trying to decide if becoming a Certified Nutritional Practitioner is right for you? Take the 3 minute holistic nutrition career discovery quiz.
Resources
1. Hermann, J. R. (2021, April 1). Protein and the body – Oklahoma State University. Protein and the Body | Oklahoma State University.https://extension.okstate.edu/fact-sheets/protein-and-the-body.html?Forwarded=pods.dasnr.okstate.edu%2Fdocushare%2Fdsweb%2FGet%2FDocument-2473%2FT-3163web.pdf
2. Protein. protein noun – Definition, pictures, pronunciation and usage notes | Oxford Advanced Learner’s Dictionary at OxfordLearnersDictionaries.com. (n.d.).https://www.oxfordlearnersdictionaries.com/definition/english/protein
3. Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. ‘The Shape and Structure of Proteins.’ Available from:https://www.ncbi.nlm.nih.gov/books/NBK26830/
4. Lopez MJ, Mohiuddin SS. Biochemistry, Essential Amino Acids. [Updated 2023 Mar 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from:https://www.ncbi.nlm.nih.gov/books/NBK557845/
5. Collagen: What it is, types, function & benefits. Cleveland Clinic. (2022, May 23).https://my.clevelandclinic.org/health/articles/23089-collagen
6. Are you getting enough protein? here’s what happens if you don’t. UCLA Health System. (2022, November 4).https://www.uclahealth.org/news/are-you-getting-enough-protein-heres-what-happens-if-you-dont
7. Department of Health & Human Services. (2003, May 21). Protein. Better Health Channel.https://www.betterhealth.vic.gov.au/health/healthyliving/protein
8. Fetters, K. A. (2018, March 30). Older adults don’t get enough of this important nutrient – US news health. U.S. News & World Report.https://health.usnews.com/wellness/food/articles/2018-03-30/older-adults-dont-get-enough-of-this-important-nutrient
9. Ferraro PM, Bargagli M, Trinchieri A, Gambaro G. Risk of Kidney Stones: Influence of Dietary Factors, Dietary Patterns, and Vegetarian-Vegan Diets. Nutrients. 2020 Mar 15;12(3):779. doi: 10.3390/nu12030779. PMID: 32183500; PMCID: PMC7146511.
10. Pasiakos SM, McLellan TM, Lieberman HR. The effects of protein supplements on muscle mass, strength, and aerobic and anaerobic power in healthy adults: a systematic review. Sports Med. 2015 Jan;45(1):111-31. doi: 10.1007/s40279-014-0242-2. PMID: 25169440.
11. Halton TL, Hu FB. The effects of high protein diets on thermogenesis, satiety and weight loss: a critical review. J Am Coll Nutr. 2004 Oct;23(5):373-85. doi: 10.1080/07315724.2004.10719381. PMID: 15466943.
12. Leidy HJ, Tang M, Armstrong CL, Martin CB, Campbell WW. The effects of consuming frequent, higher protein meals on appetite and satiety during weight loss in overweight/obese men. Obesity (Silver Spring). 2011 Apr;19(4):818-24. doi: 10.1038/oby.2010.203. Epub 2010 Sep 16. PMID: 20847729; PMCID: PMC4564867.
13. Gunnars, K. (2023a, March 30). How protein can help you lose weight naturally. Healthline.https://www.healthline.com/nutrition/how-protein-can-help-you-lose-weight
14. Bonjour JP. Dietary protein: an essential nutrient for bone health. J Am Coll Nutr. 2005 Dec;24(6 Suppl):526S-36S. doi: 10.1080/07315724.2005.10719501. PMID: 16373952.
15. Kerstetter JE, Kenny AM, Insogna KL. Dietary protein and skeletal health: a review of recent human research. Curr Opin Lipidol. 2011 Feb;22(1):16-20. doi: 10.1097/MOL.0b013e3283419441. PMID: 21102327; PMCID: PMC4659357.
16. Pasiakos SM, McLellan TM, Lieberman HR. The effects of protein supplements on muscle mass, strength, and aerobic and anaerobic power in healthy adults: a systematic review. Sports Med. 2015 Jan;45(1):111-31. doi: 10.1007/s40279-014-0242-2. PMID: 25169440.