Macronutrient Series: Protein!
In this blog post series, you’ll learn about the three major macronutrients (carbohydrates, fats and proteins) and why they’re important to your health. Each macronutrient has a significant impact on our energy levels, performance, recovery, disease risk, body composition and more. In this post, we’ll be covering Proteins.
What are Proteins?
Proteins are organic molecules made up of the elements carbon, hydrogen and nitrogen. These elements join together to make an amino acid, amino acids join to form peptides and peptides join together in a chain to form proteins. Proteins are found in 4 specific structural arrangements.
Primary Structure: Amino acids joined together to form a peptide chain.
Secondary Structure: This structure is created as amino acids bind to neighboring amino acids and other amino acids further down the chain. This structure gives the protein strength and stiffness.
Tertiary Structure: Three dimensional structure that occurs by complete folding of the sheets and helices of the secondary structure. This structure is held in position by hydrophobic and hydrophilic interactions. Various enzymes, transport proteins and immunoproteins have tertiary structures.
Quaternary Structure: This protein structure is the formed when tertiary proteins join together. Each protein is considered a separate sub-unit in this structure.
The structure of a protein molecule determines its function. Most proteins in our bodies are secondary, tertiary and quaternary structure.
Digestion, Absorption, Metabolism and Transport
The goal of the digestive process is to break proteins down into amino acids. This process begins in the stomach where hydrochloric acid denatures (breaks apart) the secondary, tertiary and quaternary protein structures. As the complex structures are denatured the proteins become peptides. Peptide bonds are broken by an enzyme called pepsin. After the stomach does its job were left with polypeptides and amino acids that are sent to the small intestine.
The Small Intestine
The pancreas secretes proenzymes ( trypsinogen, chymotrypsinogen, procarboxypeptidases, proelastase, collagenase) that meet the polypeptides and amino acids in the small intestine. These enzymes all work to break the polypeptides into single amino acids. The amino acids are then absorbed into our bloodstream by a process called active transport. Once in the bloodstream, the amino acids can be used for energy or to build new proteins such as enzymes and hormones. Amino acids can also be transported to the liver.
Most amino acids are transported to the liver. For every 100g of amino acids taken in
20g goes into systemic circulation to the plasma amino acid pool. The plasma amino acid pool is a reserve of about 100g of amino acids found in blood plasma. It contains a collection of essential and non essential amino acids. Our bodies can use amino acids from the plasma for a variety of task such as synthesizing muscle proteins, enzymes, immune system chemicals, transport proteins, skeletal/connective tissues and neurotransmitters.
20g is used for protein synthesis (14g remains in the liver and 6g is used to build plasma proteins, glutathione, carnitine, creatine and a lot more)
60g is catabolized (broken down) to produce energy, glucose, ketones, cholesterol and fatty acids.
When it comes to metabolism proteins are the last macronutrient that your body will breakdown for energy production. The body has to undergo a very inefficient process, known as gluconeogenesis, to form the carbohydrate glucose (check out a previous post about this molecule) which can then be used for energy. Instead, our body uses broken down amino acids to create enzymes to help speed up or slow down metabolic processes, maintain our structural systems, and keep our cells healthy!
Amino Acid Classification
Amino acids are divided into 3 general categories.
Non-essential: these are the 6 amino acids our body can manufacture, we do not need to eat them. (Alanine, Asparagine, Aspartic acid, Glutamic acid, Proline & Serine)
Essential: these are the 9 amino acids that our body cannot manufacture, we must eat these. (Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan & Valine)
Conditionally essential: these are 4 amino acids that we may need to eat more of when under physical stress (hard training or when sick). We’re able to synthesize these amino acids but not as effectively as the non-essentials. (Arginine, Cysteine, Glutamine & Tyrosine)
Branched Chain Amino Acids (BCAAs): are amino acids that include a side chain of one carbon atom and three hydrogen atoms. The three BCAAs are leucine, isoleucine and valine. BCAAs are the foundation for protein synthesis and energy production which makes them very important to many metabolic processes. BCAAs are also the only amino acids not broken down by the liver.
How much Protein?
Proper protein intake depends on a lot of factors (age, gender, activity level, stress level, training, goals, lifestyle, medications etc) .The baseline recommendation from the American College of Sports Medicine (ACSM) is 1.2-1.7g of protein per kg of body mass. The International Society of Sports Nutrition recommends 1.4-2.0g of protein per kg of body mass. A simple strategy is to use the palm of your hand as a measuring tool for your protein serving. Women have about 1 palm of protein per meal and men have 2 palms of protein per meal.
As human beings, we evolved eating a nutrient dense seasonal diet from a variety of food sources. We function best on a whole food diet that provides a mix of amino acids (especially essential amino acids). This can be achieved by eating a diet rich in well sourced eggs, fish/seafood, beef, pork, lamb, wildgame, cottage cheese, greek yogurt, poultry, beans, quinoa, peas, rice, sprouted grains, hemp, nuts, seeds, animal protein powders and plant protein powders.
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Sources: Berardi, J., Andrews, R., St. Pierre, B., Scott-Dixon, K., Kollias, H., & DePutter, C. (n.d.). The Essentials of Sport and Exercise Nutrition (3rd ed.).
Chek, P. (n.d.). How to Eat, Move and Be Healthy!
Rakel, D. (n.d.). Integrative Medicine (4th ed.).