Overview of Protein: Understanding Protein and the Role it Plays in your Training

Posted: Tuesday, 17 April 2012 by Strength&Nutrition24/7 in Labels:
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  1. Intro
  2. Essentials of protein
  3. Protein digestion
  4. Protein quality and methods of assessment
  5. Nitrogen balance
  6. Protein Requirements
  7. Protein timing
  8. Protein Sources
  9. Protein type
  10. Conclusion
  11. References


Intro

For over 150 years, scientists have been exploring the role that protein plays in human anatomy and physiology. In the realm of sport and exercise nutrition, there is no topic that has received more attention or heated debate then protein (Antonio, 2007). It was first hypothesized in the mid 1800s by a man named Von Leibig that protein was the main source of fuel for muscular contractions (Von Leibig, 1842). However, this was later disproved in 1925; which lead most scientists to believe that protein needs were not affected by exercise (Cathcart, 1925). Shockingly, it has only been in the last 40 years that research has come to a middle ground in terms of protein as a source of energy. In general, protein is not a major fuel source for muscular contractions, but in certain circumstances protein and/or amino acids can play an important role in muscle metabolism and exercise performance (Antonio, 2007).


Essentials of protein
Protein, fat, and carbohydrates make up the “big three” (macronutrients) (Powers, 2007; Tortora, 2009; Antonio, 2007). Of these three, only fat and protein are essential nutrients (Powers, 2007; Tortora, 2009; Antonio, 2007).  Protein and carbohydrates are similar in the fact that they both have an energy density of four Kcals per gram (Powers, 2007; Tortora, 2009; Antonio, 2007). However, protein differs from carbohydrates and fats by the nitrogen atoms. The nitrogen atoms in protein are what give the name amino (nitrogen containing) to the amino acids (Powers, 2007; Tortora, 2009; Antonio, 2007). Protein contains the nine essential amino acids (Powers, 2007). Without these amino acids, the body cannot synthesize all the proteins needed for tissues, enzymes, and hormones (Powers, 2007; Tom, 2009). The body synthesizes the various proteins through numerous combinations of amino acids linked together by peptide bonds (Powers, 2007; Tortora, 2009; Antonio, 2007). In general, the body’s proteins are polypeptides that contain over 100 amino acids linked together (Antonio, 2007).
Amino Acids

Essential
  • Histidine
  • Isoleucine*
  • Leusine*
  • Lysine
  • Methionine
  • Phenylalanine
  • Threonine
  • Tryptophan
  • Valine*


Nonessential
  • Alanine
  • Arginine†
  • Asparagine
  • Aspartic acid
  • Cysteine†
  • Glutamic acid
  • Glutamine†
  • Glycine†
  • Proline†
  • Serine
  • Tyrosine†


*Branched chain amino acid
†Conditionally essential amino acid



A good illustration to understand the difference between essential and non essential macrontruients is to illustrate two islands with people stranded on each. On the first island, there is only carbohydrates, while on the second there are only fats and protein (this is impossible of course, but humor me for the sake of the illustration). In the first few days, people on both islands are feeling alright. This indicates they have no problems. However, if we came back to the islands a month or two later, the people on the carbohydrate only island would all be dead, and the people on the protein and fat only island would be fine, perhaps sluggish and tired.

Protein digestion
The process of protein digestion begins in the stomach. In the stomach, the proenzyme pepsinogen is converted into pepsin by hydrochloric acid (Tortora, 2009; Antonio, 2007). Pepsin works to fragment protein into smaller peptides and free amino acids by cleaving the peptide bonds that link amino acids together (Tortora, 2009; Antonio, 2007). Following the digestion in the stomach, the gastric juices enter into the small intestine where the pancreatic juices (trypsin, chrymotrypsin, carboxypeptidase, and elastase) and the brushborder itself (aminopeptidases, intracellular peptidases) complete the cleavage of the peptide bonds to produce absorbable amino acids (Tortora, 2009; Antonio, 2007). The absorbable amino acids are then absorbed from the lumen of the small intestine into the blood by either cotransporter or facilitated diffusion (Tortora, 2009; Antonio, 2007). The protein that is not absorbed is converted mostly to methane (Tortora, 2009; Antonio, 2007). Thus, further research has not found a maximum amount of protein that can be absorbed in a meal (Tortora, 2009; Antonio, 2007). However, the scientific community generally agrees that humans are capable of absorbing approximately 95% of animal protein and 85% of plant protein (Young, 1994).

The amino acids that have been absorbed into the bloodstream join the amino acid pools. The amino acids are now capable of being used to synthesize proteins and other nitrogen compounds, oxidized for energy, or excreted in the urine. During bouts of exercise, amino acids are often oxidized, particularly BCAAs (leucine, isoleucine, valine) which are used in significant amounts. In order for the amino acids to be oxidized, they must go through one of two processes: 1) transamination or 2) oxidative deamination.

Note: Protein that is not absorbed is mostly turned into methane; amino acids that are not used are excreted in urine. Therefore, protein in excess is not stored, unlike carbohydrates and fat. 

Protein quality and methods of assessment

The quality of the protein you consume is very important to consider when improving your health and performance. Protein quality is the ability of a dietary protein to support one biological growth and maintenance (Schaafsma, 2005). Protein quality is most commonly measured by three methods:

  1. Biological value (BV)The purpose of BV is to measure the amount of nitrogen retained in comparison to the amount absorbed (Antonio, 2007). The values of different food proteins are determined through experimentation on humans and laboratory animals (Antonio, 2007). It is extremely difficult to determine nitrogen retention; in fact it is so difficult to determine that research has historically over estimated nitrogen retention in humans. Even with the difficulties involved with this assessment method, it is still considered a valid form of assessing protein quality (Fuller, 1994)
  2. Protein efficiency ratio (PER)The purpose of PER is to measure its ability to support the growth and weaning of rats. This method looks at the amount of weight gained over the amount of protein consumed (Antonio, 2007). This is a less ideal form of measuring protein quality since it looks at rats and not humans. Further, the assessment does not attempt to assess what is needed for an adult to maintain health.
  3. Protein digestibility-corrected amino acid score (PDCAAS) This method is relatively new and a very effective way of measuring protein quality. Its purpose is to assess protein quality for children older than one and non pregnant adults (Antonio, 2007). This is assessed by comparing the amino acid profile of a specific dietary protein against the essential human amino acid requirements that have been determined by the Food and Agriculture Organization (Antonio, 2007). This is then corrected by taking the digestibility differences into consideration (Antonio, 2007). The dietary protein is then given a rating between 0-1, with 1 meaning that the protein exceeds the dietary needs of the body (Antonio, 2007). The down side of this assessment is the cost, which has stopped this from being used in nutritional facts thus far.



Figure 1

Nitrogen balance
The amount of protein to be consumed by general public and athletes has been generally determined by nitrogen balance studies. The liver, skeletal muscles, and blood make up the amino acid pools of the body. When the amount of nitrogen enters these pools at the rate it excretes the body, it is at equilibrium (nitrogen balance). The body is in a constant battle to maintain the nitrogen balance. In general, periods of overtraining and fasting equates to a greater loss of nitrogen then intake and a state of negative nitrogen balance takes place. However, when lean body tissues are in a state of hypertrophy the opposite occurs (positive nitrogen balance). This is generally measured by nitrogen intake from food versus nitrogen output in urine, sweat, and feces. This form of study is simple to understand, but is very difficult to perform and have historically overestimated nitrogen retention in humans (Fuller, 1994).

Protein Requirements
Athletes who participate in intense training have been found to require a higher dietary protein need than individuals who do not train (Kerksick, 2006; Kreider, 1999; Lemon, 1992; Maclean, 1993; Lemon, 1997; Lemon, 2000; Tipton, 2004; & Tarnopolsky, 1992). However, not all research agrees with the findings that physically active individuals require a greater amount of protein than the current suggestions (Rennie, 2000). Many factors may also play a role in the amount of protein required, such as, energy intake, exercise intensity, exercise duration, training status, and gender (Lemon, 1997; Lemon, 2000; Tipton, 2004; Rennie, 2000; Lemon 1991; Lemon, & Proctor, 1991; Rankin, 1999; Tranopolsky, 2004; & Lambert, 2004). With this in mind, and understanding that protein intake for optimal health/performance is yet unclear; below is a list of the current RDA recommendations for protein intake for sedentary adults, along with values for different forms and statuses of exercise.
Table acquired from Antonio, 2007
Activity Level g/kg body weight

  • Sedentary 0.8 (0.4g/lb)
  • Recreational exerciser 1.0-1.4 (0.5-0.7g/lb)
  • Wt training (maintenance) 1.2-1.4 (0.6-0.7g/lb)
  • Wt training (muscle gain) 1.4-1.8 (0.7-0.9g/lb)
  • Endurance training 1.2-1.4 (0.6-0.7g/lb)
  • HIIT 1.2-1.8 (0.6-09g/lb)
  • Weight-restricted sports 1.4-2.0 (0.7-1g/lb)

Teens are recommended to take an additional 10%

Protein timing
When considering the nitrogen balance concept, we see that when the balance is positive, skeletal muscle mass will increase (Tang, 2009; Fry, 2009; Kraemer, 2002; Kraemer, 1998; & Hulmi, 2010). Conversely, a negative nitrogen balance involves a reduction in skeletal muscle mass (Tang, 2009; & Hulmi, 2010). It has been clearly demonstrated that acute bouts of heavy resistance exercise and/or intermittent exercise of repeated short and high intensity bouts significantly raises the body’s ability to synthesise muscle protein (Tang, 2009; Hulmi, 2010; American, 2009). However, nitrogen balance remains in the negative because muscle protein breakdown occurs at an even greater rate in a fasted state (Biolo, 1995; Tipton, 1999; Pitkänen, 2003).  This can be avoided by the ingestion of protein or essential amino acids pre and/or post training, and produces a positive nitrogen balance (Tipton, 1999; Tipton, 2007; Wilkinson, 2007; Koopman, 2005; Tang, 2007; Moore, 2009; Katasanos, 2008; Ivy, 2004; & Tang, 2009). By creating a positive nitrogen balance through ingestion of protein and essential amino acids, pre and/or post exercise can enhance hypertrophy in response to chronic resistance training (Andersen, 2005; Bird, 2006; Cribb, 2007; Hartman, 2007; Burke, 2001; Candow, 2006; Kerksick, 2006; Willoughby, 2007; & Hulmi, 2009). Hypertrophy can be further enhanced by ingesting protein and essential amino acids within an hour of training (Esmarack, 2001; Cribb, 2006). A multitude of studies have demonstrated that there is a two hour window of opportunity, post exercise (Ivy, 2004; Ivy, 1988; Esmarack, 2001; Anderson, 2005;  & Levebhagen, 2001). After a mere 45 minutes, this window already begins to close. During this time, your muscles are extremely insulin receptive. In the 45 minutes of high insulin sensitivity, the body is in a state in which it can stimulate glucose storage and protein synthesis. Because of this ability, insulin has earned the title “anabolic regulator of the muscle.” Due to this, insulin may in fact, be the most important hormone to increase muscle strength and mass (Ivy, 2004). This 45 minute window is incredibly significant, if you ingest high glycemic carbohydrates and protein during it, you can reduce your recovery time by 16-24 hours (Ivy 2004).  


 
Figure 2

A study completed by Anderson in 2005 looked at the effect resistance training and combined with timed ingestion of protein on muscle size and strength. The study found that young men who supplemented with 25g of protein before and after training had an 18-26% greater increase in muscle hypertrophy than men who consumed 25g of high glycemic carbohydrate pre and post exercise. Another study completed by Roy was the influence of post-exercise macronutrient intake on energy balance and protein metabolism in active females, participating in endurance training. It is found that, women who were performing a 7 day intense cycling exercise program, had a reduced body weight loss and improved nitrogen status when post exercise macronutrient supplementation took place. Research has further demonstrated greater insulin response and glycogen synthesis when protein and carbohydrates are ingested together, rather than carbohydrates alone (Ivy, 2002; Zawadzki, 1992; & Williams, 2003).  However, it is interesting to note when a high amount of carbohydrates are ingested in the immediate 4 hours because after exercise, little added benefit occurs (further supporting the 2 hour window) (Carrithers, 2000;&  Jentjens, 2001). It has also been found that the ingestion of protein, amino acids, and carbohydrate causes greater increase in muscle protein synthesis than carbohydrate and protein alone (Borsheim, 2004). It has been well established that most athletes obtain adequate amounts of protein through their diets alone. However, these studies demonstrate that timing of protein ingestion is of greater importance then quantity.  Figure2 is a table by Ivy 2004, which shows the recommendation on protein shakes for pre, during, and post training. 


Figure 3

Protein Sources
There is a wide variety of protein sources which vary greatly in amino acid profile, digestibility, and nutritional value. Protein is only considered “complete” when it contains all nine of the essential amino acids. Tissue growth and repair can only take place when all the amino acids are present. Sources of complete proteins include animal protein such as eggs, meat, poultry, fish, and dairy. Further complete proteins are almost nonexistent in non animal products. Some examples are hemp, soy, chia, and sacha inichi. Proteins that lack some of the essential amino acids are called “incomplete,” if not combined with complementary foods, growth will not occur, and instead malnutrition is likely to occur. Sources of incomplete proteins far exceed complete proteins, such as, plant proteins. Several examples are corn, lentils, beans, fruits, and nuts. 


Figure 4


Protein type
The type of protein we consume has a significant effect on promoting improvements in strength and body composition. A great deal of studies have demonstrated that animal proteins are superior to vegetarian and that milk is greater than hydrolyzed soy proteins (Campbell, 1999; & Phillips, 2005). Further research has demonstrated that consuming amino acids and proteins rich in non essential amino acids has no added benefit; this was reviewed in Tipton’s 2004 study.

Is casein or whey a better choice for post workout supplement? Both forms of protein are fantastic in themselves. However, it depends on the time of ingestion in relation to exercise which will decide what is better suited (Philips, 2010). When looking at the two hours post training ,whey is anabolic, fast digestibility, and increases protein synthesis (Philips, 2010; Boirie, 1997). As noted before, the window in which protein is used most effectively is within 45 minutes post training. In order to utilize this time as best as possible, one needs the protein to digest as quickly as possible. Therefore, whey protein is superior within proximity to training (Philips, 2010). Casein is superior before bed, due to its slow digestibility and ability to inhibit protein breakdown (Philips, 2010; Boirie, 1997; Dangin, 2001; Tang, 2009). This provides the body with a “trickle” of amino acids over a long period of time (Philips, 2010; Boirie, 1997; Dangin, 2001; Tang, 2009).  In the only head to head studies of casein vs whey, casein supplementation resulted in greater gains in strength, muscle mass, and fat loss (Antonio, 2008; & Demling, 2000). Both whey and casein have benefits and provide enough reason for both to be used.


Conclusion
Protein has been researched in incredible depth over the last 150 years. There is still a great deal of debate amongst researchers and information missing. However, one can conclude that protein is essential for health and performance. Protein is essential in increasing muscle mass and strength. With the proper timing of protein ingestion one can have dramatic improvements in strength and muscle hypertrophy. When deciding on what kind of protein to consume, there is clear evidence that animal protein is superior to vegetarian protein. Finally, by taking advantage of the unique benefits of whey and casein one can significantly improve athletic performance.

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Figures
  • Figure 1: http://www.nutritionexpress.com/article+index/authors /editor /showarticle. aspx?articleid= 743
  • Figure 2: http://www.nutridesk.com.au/post-exercise-metabolic-window.phtml
  • Figure 3: Ivy J, & Portman R. Nutrient timing: the future of sports nutrition. Laguna Beach, CA: Basic Health Publications, 2004. Print.
  • Figure 4: http://tigerfitnessla.com/blog/wp-content/uploads/2009/06/protein-compliments-vegan.jpg



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