The Importance of Protein

Written by Iron Vegan

Protein. You know it’s important – in fact, it’s derived from the Greek word proteios meaning “of first importance”!¹ It plays an important role in the growth and repair of tissues including muscle and bone. Here’s a bit more about it, and some of its other benefits!

Protein Defined

It’s the major structural component of all cells in the body¹, and it’s one of the three macronutrients (the other two are fats and carbohydrates).¹

Amino Acids

Organic compounds that combine to form proteins, amino acids are often referred to as the building blocks of proteins. ¹ They play a crucial role to your body and are essential to vital processes like synthesizing hormones. ¹ There are 3 categories of amino acids²:

1. Essential: we can’t make them on our own and must get them through our diet²: Histidine, Isoleucine*, Leucine*, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine*

2. Non-Essential: our body makes these ones on its own: Alanine, Aspartic acid, Asparagine, Glutamic acid, Serine²

3. Conditionally Essential: our bodies can make these, but only under certain conditions (e.g., early life, disease states, intense exercise, stress, etc.)²: Arginine, Cysteine, Glutamine, Glycine, Proline, Tyrosine

Branch-Chain Amino Acids* (BCAA) are the most anabolic (tissue/muscle building) of all the amino acids.² 3 essential amino acids are classified as BCAA: Leucine, Isoleucine, Valine. ² Leucine plays the biggest role in stimulating the synthesis of muscle.²

Several organs are involved in amino acid metabolism, including:³

• Intestine: dietary amino acids are absorbed in the small intestine; the intestine prefers glutamine and asparagine for energy³

• Liver: catabolism (the breakdown of large molecules) of all amino acids except for branch-chain amino acids begins in the liver. The amine group is separated and incorporated into urea. Carbon skeletons are oxidized to Co2 or H20; or used for gluconeogenesis (which is the generation of glucose from certain non-carbohydrate carbon substrates) or ketogenesis (the breakdown of fatty acids and ketogenic amino acids)³

• Muscle: branch-chain amino acids are degraded primarily in muscle. Over 50% of the amino acids released to the circulation are alanine and glutamine, which act as carriers of amines from other tissues³

• Kidney: captures glutamine released from muscles. Reactions produce ammonia, which is excreted in urine. This is one of the mechanisms to help maintain the body’s acid-base balance³

What is a Complete vs. Incomplete Protein?

A complete protein contains all 9 of the essential amino acids. Proteins derived from animals (meat, fish, seafood, eggs, dairy) are considered complete proteins.^4,5,6

An incomplete protein is a protein that’s missing 1 or more of the essential amino acids or has an inadequate dietary essential amino acid balance.^4,5,6While many plant-based proteins are considered incomplete, combining amino acids together in a meal will typically provide all the amino acids the body needs.^4,5,6 Provided you eat all of the essential amino acids throughout the day, your body can piece it all together.^4,5,6

Benefits of Protein

Muscle

Skeletal muscle mass is in a constant state of turnover, with muscle proteins being synthesized and broken down simultaneously throughout the day. ⁷ Nutrition plays an important role in daily muscle protein turnover. Specifically, amino acid intake increases muscle protein synthesis rates (and inhibits muscle protein breakdown rates to a lesser extent). ⁷

Weight Management

Higher protein intake increases thermogenesis and satiety compared to diets of lower protein content. Research also suggests that high protein meals lead to a reduced subsequent energy intake:⁸

• Protein intake stimulates metabolic hormones that communicate information about energy status to the brain; and involve brain regions that influence reward and motivation⁹
• Higher-protein diets (1.0-1.5 g/kg body weight) are associated with lower BMI and waist circumference and higher HDL cholesterol compared to protein intakes at RDA levels¹⁰

Bone Health

High dietary protein intake may positively impact bone health in several ways, including calcium absorption and enhancing lean body mass.¹¹ It’s an important nutrient for bone health and for the prevention of osteoporosis.¹² Protein helps give your bones their strength and flexibility, and is also the big component of muscles.¹²  

Mental Health

Sufficient protein intake is an important part of neurotransmitter production.¹³ The essential amino acid methionine combines with adenosine triphosphate (ATP) to produce S-adenosylmethionine (SAM), which facilitates the production of neurotransmitters in the brain. ¹³ The neurotransmitter dopamine is made from the amino acid tyrosine and the neurotransmitter serotonin is made from the tryptophan. ¹³ If there’s a lack of any of these two amino acids, there will not be enough synthesis of the respective neurotransmitters, which is associated with low mood and aggression.¹³

Protein intake and in turn the individual amino acids can affect brain function and mental health¹³.

 

References:

1. Wu, G. (2016). Dietary protein intake and human health. Food Funct., 7, 1251 doi: 10.1039/c5fo01530h
2. Britannica Online. Accessed April 10, 2002 https://www.britannica.com/science/amino-acid
3. Antonio Blanco, Gustavo Blanco (2017). Role of Various Organs in Amino Acid Metabolism. Medical Biochemistry https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/amino-acid-metabolism
4. Westerterp-Plantenga, M., Lemmens, S., & Westerterp, K. (2012). Dietary protein – its role in satiety, energetics, weight loss and health. 108(S2), S105–S112. https://doi.org/10.1017/S0007114512002589
5. Fürst, P. (2009). Basics in clinical nutrition: Proteins and amino acids. e-SPEN, the European e-Journal of Clinical Nutrition and Metabolism, 4(2), e62–e65. https://doi.org/10.1016/j.eclnm.2008.07.010
6. Deutz, N. (2008). Basics in clinical nutrition: Protein and amino acid metabolism. e-SPEN, the European e-Journal of Clinical Nutrition and Metabolism, 3(5), e185–e187. https://doi.org/10.1016/j.eclnm.2008.06.002
7. Wall, B.T., Cermak, N.M. & van Loon, L.J.C. Dietary Protein Considerations to Support Active Aging. Sports Med 44, 185–194 (2014). https://doi.org/10.1007/s40279-014-0258-7
8. Halton, T. & Frank B. Hu. (2004) The Effects of High Protein Diets on Thermogenesis, Satiety and Weight Loss: A Critical Review, Journal of the American College of Nutrition, 23:5, 373-385, DOI: 10.1080/07315724.2004.10719381
9. Cuenca-Sanchez, M., Navas-Carrillo, D., Orenes-Pinero, E. (2015). Controversies Surrounding High-Protein Diet Intake: Satiating Effect and Kidney and Bone Health. Advances inNutrition. May;6(3): 260-266.
10. Pasiaskos, SM, Lieberman, HR, Fulgoni, VL. (2015). Higher-protein diets are associated with higher HDL cholesterol and lower BMI and waist circumference in US adults. The Journal of Nutrition. Mar;145(3):605-14.
11. Kerstetter, J. E., Kenny, A. M., & Insogna, K. L. (2011). Dietary protein and skeletal health: a review of recent human research. Current opinion in lipidology, 22(1), 16–20. https://doi.org/10.1097/MOL.0b013e3283419441
12. (n.d.). Osteoporosis Canada. Retrieved January 25, 2021, from https://osteoporosis.ca/bone-health-osteoporosis/nutrition/protein/
13. Rao, T. S., Asha, M. R., Ramesh, B. N., & Rao, K. S. (2008). Understanding nutrition, depression and mental illnesses. Indian journal of psychiatry, 50(2), 77–82. https://doi.org/10.4103/0019-5545.42391