The Role of Protein in Training

Proteins are indeed the building blocks of the body. They also play a vital role in resistance and aerobic training.

The role of protein and amino acids in building body tissue is well known. Amino acids are the end product of ingesting protein. Amino acids are used for three basic functions in the body:

  • They provide material for body tissue repair and synthesis.
  • They are the synthesis of hormones, enzymes, and blood proteins.
  • They provide for energy through deamination.

Specific amino acid combinations are predetermined through genetic nitrogenous base coding to be synthesized into living body tissues, muscle tissues, hormones, and blood proteins.

While other specific amino acid combinations are synthesized by the liver into the very enzymes and hormones that convert free amino acids, body protein and fatty tissue, into energy through deamination and catabolism.

Deamination is the removal of an amino group, NH2, from an organic compound. It is the process by which amino acids are broken down if there is an excess of protein intake. This process takes place primarily in the liver. It is important to note that whenever energy is produced, some amount of amino acid deamination is unavoidable. It is equally important to realize that free amino acids are available in the bloodstream for 3-4 hours for combining with other amino acids for the uptake and synthesis of body tissues.

If after this approximate length of time, amino acids are still free in the bloodstream, they will be degraded and/or deaminated by liver enzymes into energy. This amino acid deamination results in the toxic bi-product ammonia, which the liver then converts into urea nitrogen for excretion. The amino group is removed from the amino acid and converted to ammonia. The rest of the amino acid is made up of mostly carbon and hydrogen, and is recycled or oxidized for energy.

Enzymes convert ammonia to urea or uric acid through the addition of carbon dioxide molecules in the urea cycle, which also takes place in the liver — and is not a deamination process. Urea and uric acid can safely diffuse into the blood and then be excreted in urine.

How much protein is too much?

The most accurate way of determining sufficient protein intake is to closely monitor the nitrogen intake (16% of all protein is nitrogen), and then compare this amount to the excreted nitrogen through Urinary Urea Nitrogen (UUC) testing.

There are two primary metabolic conditions during which a high protein level exists:

  • In the presence of sufficient total calories, a level of protein intake that is greater than the body’s need will likely result in a positive nitrogen balance, but at the expense of over stressing the liver, which is already lcharged with breaking down the toxin ammonia into urea for excretion. The greater the excess amino acids the harder the liver has to work. Overabundant amino acid presence in the blood accelerates metabolism and more water is lost during these increased chemical reactions, possibly causing dehydration in varying degrees. An alternative to decreasing the protein intake under these conditions is the consideration of increasing the intensity of exercise. This will minimize the excess circulating amino acids. The best way to optimize protein intake is through UUN testing and then altering resistance training intensity.
  • In the absence off sufficient calories, whether protein ingestion is high or not, a high level of circulating “broken-down” body proteins and resulting amino acids will result in a negative nitrogen balance, as well as the liver’s production of keto acids, which are toxic to brain function. This, low-calorie, overabundant amino acid presence is clearly a more critical metabolic situation than when total calories are sufficient, as mentioned earlier, and it is undesirable regardless of health and fitness goals. This situation occurs during prolonged and extreme dieting.

Of course, any fat loss goal and takes a back seat whenever health is threatened. Maximizing fat loss results does sometimes call for a substantial restriction of total calories, however, using acetate testing (similar to UUN testing), adjustments to total calories can be made that result in a less threatening trace measurement of acetate.

It is important to keep in mind that increasing protein intake while also reducing carbohydrate intake with fat loss in mind will have positive fat loss effects, since amino acid deamination constitutes more work and accelerates metabolism. However, it is not suggested to maintain an extremely low calorie, high protein intake for periods longer than a few weeks. Increased water intake must be an integral part of this short-term dietary fat loss measure.

How low is too low?

In the presence of sufficient total calories, low protein ingestion will not easily accommodate the building of new tissue. It becomes extremely important, if one is ingesting little or no protein, that energy needs are being completely provided by ingested carbohydrates and fats, thus allowing what few amino acids are present in the blood to be synthesized from body proteins to include muscle tissues.

When too little protein is being ingested and intense resistance training is performed, catabolism is prolonged and a long-term negative nitrogen balance can be expected.

While there is known that several natural complex carbohydrates contain protein, it is acknowledged that several essential amino acids are missing from these carbohydrates.

In most cases, when ingested proteins are insufficient even for the required synthesis and repair of vital blood proteins and organ tissues, the body uses catabolic enzymes to degrade existing ‘low priority’ body tissues using their bi-products as building blocks instead. Since antibodies, for example, are among these ‘unneeded’ body tissues that are cannibalized, the body’s immune system can suffer as a result.

In the absence of sufficient total calories, while performing little or no strenuous activity, it is likely that few amino acids will escape the deamination process. In addition, the synthesis of protein based hormones, enzymes, blood proteins and various body tissues will be compromised. The performance of strenuous resistance exercise under these low-calorie, low- protein dietary conditions will likely result in the continued cannibalism of various structural body tissues to include muscle and organ tissues.

Optimizing Protein Intake

In an effort to maintain a “positive nitrogen balance” (ingesting more nitrogen than excreting), the intention should be to provide a steady flow of ingested protein (every 3-4 hours), consisting of a wide variety of amino acids allowing for all possible combinations. Thus, insuring the continued synthesis of body tissues, proteins and enzymes (positive nitrogen balance). It is important to realize that amino acids are most effectively spared from the process of deamination in the presence of sufficient bloodglucose energy that results primarily from carbohydrate ingestion. So long as protein intake is sufficient, the ingestion of more total carbohydrate calories will contribute to a positive nitrogen balance.

In addition, similarly to glucose, insulin must carry amino acids into muscle tissues, and carbohydrate ingestion causes insulin release, so it would make good sense to ingest proteins with carbohydrates to optimize insulin-carried amino acid uptake and utilization in body tissues.

All protein foods have varying Protein Efficiency Ratios (PERs), with milk and egg proteins rating highest on the list of “complete” proteins. The steady provision of protein throughout the day will generally result in a positive nitrogen balance. Where activity is concerned, the greater the intensity and duration of resistance exercise, the greater the required protein ingestion.


For those who are not currently training for size and strength, consider letting the level of activity dictate protein intake. For example, if someone trained today with at a greater intensity than usual, then consider ingesting additional proteins every 3-4 hours. If exercise intensity was somewhat low today, then concentrating protein intake will not be as important. For an endurance athlete performing aerobic activity for 60 + minutes, consider the ingestion of proteins rather than carbohydrates during the activity. Protein ingestion may act to maintain blood sugar levels longer.


These resources are for the purpose of personal trainer growth and development through Continuing Education which advances the knowledge of fitness professionals. This article is written for NFPT Certified Personal Trainers to receive Continuing Education Credit (CEC). Please contact NFPT at 800.729.6378 or [email protected] with questions or for more information.
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