NASM CNC Chapter 6: Protein
NASM CNC Chapter 6: Protein

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Chapter Goals:

  • Explain the functions and the structure of protein.
  • Describe absorption and digestion of protein.
  • Find the total daily protein requirements for different types of clients.
  • Discuss the methods for establishing the requirements for protein in diet programs.
  • Explain the myths of the hot topics regarding protein.
  • Know the role and guidelines for protein for clients.


Protein is discussed more so than any other topic in nutrition for sports. This is due to it playing such a large role in recovering from exercise, and it being involved in most bodily processes and functions. 

Protein structure

Like all other organic molecules, protein is comprised of carbon, hydrogen, and oxygen. It is, however, unique in that it contains the molecule nitrogen. These four molecules come together to make the building blocks of protein that are called amino acids.

Amino Acids

All protein is made up of amino acids. We have hundreds of amino acids found throughout nature, but there are only 20 that the human body needs to do its various functions. The structure of amino acids has 5 main parts:

  • A central carbon. 
  • A carboxyl group.
  • A hydrogen.
  • An amino group.
  • A side chain.

Essential amino acids are the amino acids that we need to make sure to stay in our diet due to the necessity of them in bodily functions, and their inability for being synthesized in the body. We have 9 Essential Amino Acids, or EAAs:

  • Histidine
  • Lysine
  • Methionine
  • Phenylalanine
  • Threonine
  • Tryptophan
  • Isoleucine
  • Leucine
  • Valine

Amino acids may also be classified based upon their ability to be glucose or ketones for their use in metabolism. 

Protein Synthesis

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When consumed, proteins need to be broken down to their amino acids first during digestion, and then they can be absorbed into the intestines. Protein synthesis is the process where amino acids are put together in order to form proteins like muscle. 

Dehydration synthesis is the process through which the amino acids are bonded together. The opposing process is known as hydrolysis and this breaks down proteins into the amino acids. 

A dipeptide is when two amino acids are joined together. A tripeptide is when three amino acids are joined. Between 4 and 9 amino acids together is known as an oligopeptide. 10 or more chains of amino acids will be called a polypeptide. 

Protein Digestion and Absorption

The first step to breaking down proteins is known as denaturation. This is changing the protein’s shape, but not the actual structure itself. This denaturing of the protein happens as a response to a variety of factors including temperature, enzymes, and ph levels. These all work in times of protein digestion and absorption. Most proteins actually begin this denaturation with the cooking of the foods. And then the other factors manifest with mastication and the acidic environment of the stomach. After the stomach passes the food to the small intestine, the secretin and cholecystokinin works to break them down further and eventually into single and pairs of amino acids. They can then be absorbed from the small intestine and into the hepatic portal vein and carried to the liver.

Protein Function

Fats and carbs are thought of as the macronutrients we use for energy, and the proteins should be seen as the macronutrients that we use for structure and function of the body. It is possible for protein to be used as energy, but this is more of a last resort for the body, or if there happens to be an abundance of protein taken in. 

Proteins and their amino acids are used throughout the body for the main functions of creating bodily tissues, forming enzymes and transports for cellular things, signaling other cells, maintaining the balance of fluids, buffering the acids and the bases, producing hormones and neurotransmitters, and also within the immune system. 

Bodily tissues

Most of our proteins within the body are held in the musculoskeletal system. We do not have a true storage system for proteins like we do for the carbohydrates and for fats. Proteins make up the actual physical structure for the bones and the muscles. So, the only way to supply them is by breaking these tissues down, and that is not what the body prefers to do.

Bones are formed from very strong collagen proteins that are found in skin, tendons, joints, and ligaments. Collagen is formed in a triple helix, giving it amazing tensile strength. The function of collagen is providing structural integrity. Alongside the collagen, we often see elastin. This gives elasticity to certain parts. Keratin is another protein found in human hair and in the fingernails. 

Enzymes and Cellular Transports

Almost all enzymes are made out of proteins. These enzymes act as the catalysts for chemical reactions and they are needed for carrying out the many functions in the body, with a primary need for them in the metabolism of foods. We find enzymes in our saliva, the stomach, fluids in the intestines, the blood, and most cells in the body. 

Cell Signaling 

The amino acid concentration may be seen by the nervous system as a signal for particular functions to be performed. Depending on the amino acid that is low, the body will signal a variety of things. 

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Fluid Balance

Proteins help to keep the fluid balance on the cell level. This is done through the part of their role as transporters across the membraned, allowing the water to move into each cell and the blood. The protein known as albumin is in charge of managing the balance of fluids. 

pH Balance

Proteins and amino acids both help in the regulation of the acid and base balance through the binding of free hydroxyl groups or hydrogen ions within our blood for the maintenance of a neutral pH.

Hemoglobin is one of the most known proteins for this balance. 

Hormones and Neurotransmitters

Many of the hormones are made up from amino acids, and we call these peptide hormones. Insulin and leptin are both other examples of these peptide hormones. 

Peptide hormones also have the ability to function as a neurotransmitter. They transmit messages chemically in the body. Peptides can belong to the nervous system as a neurotransmitter, or to the endocrine system as a hormone.

Immune System

The white blood cells require proteins in order for them to function properly throughout the immune system. The white blood cells produce antibodies, which are the proteins, and they protect the body by killing invaders and leaving friendly cells alone.

Protein Dietary Needs

Getting the right amount of protein in our diet is very essential for athletes and even the general population. We discussed what the population uses it for, but when it comes to athletes, additional protein is important for the recovery and repair of the muscles. Many athletes will need more protein than the average person.

Dietary Reference Intakes

These are established by the Food and Nutrition Board of the Institute of Medicine. The RDA, or recommended dietary allowance, is 46 grams per day for women, and 56 grams per day for men. The more specific amounts are determined by multiplying your weight in kilograms by 0.8. 

Total Daily Protein Requirements

  • Activity level of none and no exercise = 0.8 – 1.2 grams per kilogram of bodyweight.
  • Light to moderate activity level doing regular cardio = 1.2 – 1.6 grams per kilogram of bodyweight.
  • Light to moderate activity level doing regular resistance exercise = 1.5 – 2.0 grams per kilogram of bodyweight.
  • Moderate to vigorous activity level doing regular cardio = 1.5 – 2.0 grams per kilogram of bodyweight.
  • Moderate to vigorous activity level doing regular resistance exercise = 1.7 – 2.2 grams per kilogram of bodyweight.

Protein Quality

The second most important thing we need to consider regarding the protein we require is the type of protein we are taking in.

 The protein quality refers to the amount of essential amino acids found in the food and the digestibility of that protein. 

A complete protein is a protein that contains all of the essential amino acids that we need in the right amount. 

A complimentary protein is what is present when there are two incomplete proteins, that, when consumed together they will mimic one complete protein by having all of those essential amino acids. 

Special Considerations – Leucine

Leucine is a primary factor for increasing the muscle protein synthesis and facilitating muscle growth and recovery. It is the only one that is capable of enhancing the anabolism of muscles. 

Protein Timing

Most people do not need to worry about the timing for which they receive their protein. This is because most people will naturally consume the right amount just by having a balanced diet. 

For athletes, though, it is a tad different. It is possible to time the intake of protein for slight improvements to be made over the long term. These strategies should be reserved for the very dedicated people. 

It is usually more optimal for us to take in protein in smaller amounts more times per day, than to get the protein all at once. This is less true when it goes up to equal spacing of 8 meals in a day. The ideal has been shown to be 4 meals per day at around 21 grams of protein each meal. 

Carbohydrates taken in at around a 3:1 or 4:1 ratio of carb to protein is perfect.

NASM CNC Chapter 6: Protein 4
NASM CNC Chapter 6: Protein 5
NASM CNC Chapter 6: Protein 6

Tyler Read

Tyler Read, BSc, CPT. Tyler holds a B.S. in Kinesiology from Sonoma State University and is a certified personal trainer (CPT) with NASM (National Academy of sports medicine), and has over 15 years of experience working as a personal trainer. He is a published author of running start, and a frequent contributing author on Healthline and Eat this, not that.

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