In relation to bodybuilding, protein is viewed as a key nutrient in the development of strength and size. Anecdotally most bodybuilders would say that the more protein the better, on the other hand most sports dieticians take the opposite view in that protein is abundant in the average diet and if energy requirements are meet there's a good chance that protein requirements will also.
Protein is essential for life. It provides the building blocks for tissue, hormones, enzymes and accounts for 15% of the body. The building blocks it provides are amino acids and different proteins provide different amino acids and ratios of amino acids.
Amino acids fall into two distinct categories, either essential (those that cannot be produced from other amino acids by the body) or non essential. The essential amino acids are listed in figure 1, depending upon certain conditions, other amino acids are sometimes considered to be essential, giving the term 'conditionally essential'.
Figure 1 - Essential (indispensable) amino acids:
Protein's Physical Roles
As well as being an energy-providing macronutrient, protein plays a variety of vital roles within the body. These are usually grouped according to their function within the body and include:
The amino acids are used to create enzymes which allow the various metabolic functions of the body to operate efficiently.
2. Structural Components:
Proteins are used to form the various tissues of the body and can be divided into one of two groups. Contractile proteins include the components of the muscle which produce force namely actin and myosin. Fibrous structural proteins include the soft tissues of the skeletal system such as collagen, elastin and keratin.
Amino acids form the immune systems defence of immunoglobulins and antibodies.
4. Transports Proteins:
Many chemicals need to be transported throughout the body and transport proteins such as albumin, hemoglobin and myoglobin provide this role.
As well as these direct effects dietary protein can have several direct physiological ramifications which may be advantageous to a physique orientated athlete. These include:
1. Increased Satiety:
Protein will have an effect on how full we feel after eating which may go some ways to decreasing overall calorie consumption.
2. Increased Thermogenosis:
To digest protein is metabolically expensive and diets higher in protein will lead to increased dietary induced thermogenosis.
3. Increase Protein Synthesis:
By increasing protein intake you will increase protein turnover and as will be discussed later this is possibly a beneficial effect.
Protein requirements has been endless debated and as yet there is still no definitive answer. The problem arises with the fact that protein metabolism is highly complex and is effected by a myriad of other physiological and nutritional factors. The initial factor is the protein itself.
Different proteins have differing levels of amino acids and as such stated earlier can be classed as complete if they contain all the essential amino acids or incomplete if the lack one or more amino acids at the required level. There are a variety of ways in which protein quality can be determined which include:
1. Chemical Score:
A proteins amino acid levels are compared to a determined requirement level. These levels reflect the levels and ratios needed for humans and the chemical score is determined by the lowest essential amino acid level compared to the standard.
For example an egg has all the required amino acids in levels equal to or greater than the predetermined requirements and as such is given a score of 100. Another protein source may only have 80% of one of the predetermined amino acid levels and as such will be given a score of 80. If a protein has several limiting amino acids the lowest one determines the score.
|AMINO ACID SCORE|
2. Biological Value (BV):
This indicates the amount of nitrogen retained in the body. It's tested by assessing the urinary and faecal nitrogen excretion of a nitrogen (protein) free diet and that of the test protein fed.
The protein free diet allows the assessment of how much nitrogen is lost even when no protein is consumed and is considered obligatory losses. The losses seen on the test protein diet are compared and the proteins BV show how much nitrogen is retained compared to the amount absorbed.
3. Protein Efficiency Ratio (PER):
This represents the bodyweight gained on a test protein divided by the protein consumed. Usually the PER of a protein is compared to a test protein which is typically casein. If the PER has a lower score than casein it is deemed that a higher amount of protein is required to meet needs.
|PROTEIN EFFICIENCY RATIO (PER)|
Another factor which can determine an individual's protein requirement includes energy balance. If an individual is in a hypocaloric state then normal levels of protein which maintain nitrogen balance in an energy balanced diet will not be sufficient to maintain nitrogen balance (Munro 1951). As such it appears that a diet sparse in energy requires more protein to maintain a nitrogen balanced state.
It's is not only the amount of energy but also the composition of the diet which can modify protein needs. For example adequate carbohydrates are needed to ensure that protein utilization does not occur during exercises. This is due to low glycogen stores activating catabolic enzymes such as BC oxacid dehydrogenase which allows protein to be used for energy and increases the protein need (Lemon and Mullin 1980).
The mode of exercise (intensity and duration) as well as factors such as age and gender play a role in the determinates of requirements (Williams and Devlin).
To determine how much protein an athlete needs there is usually an investigation using the technique of nitrogen balance, which is possible as protein is the only macronutrient to contain nitrogen. Nitrogen balance is measured by the amount of nitrogen ingested and measuring the amount excreted through a variety of ways including faeces, urine and sweat.
If the amount of nitrogen going into the body is less than that excreted the individual would be deemed to be in a negative nitrogen balance. If the amount going in is greater than that excreted its thought that the individual is in a positive nitrogen balance state.
If the amount going in is equal to the amount going out the individual is deemed to be in nitrogen balance, which indicates the person is consuming enough protein to meet their needs.
Considering this: most protein studies have looked at the amount necessary to ensure that an athlete is in nitrogen balance. As discussed there are a variety of factors which affect the requirements from energy balance, dietary composition and gender to age and environment.
For simplicity sake the papers relating to protein needs and exercise type will be reviewed but the trainee should consider aforementioned factors when determining their intake.
1. Endurance Athlete:
For an endurance athlete their is usually very little structural protein increases (myofibrilar protein) but there is dramatic increases in enzymatic/mitochondrial protein utilization.
Tarnopolsky et al (1988) showed that young trained endurance athletes required in the region of 1.37g/kg a day to maintain nitrogen balance and these findings were supported by other researchers (Meredith et al 1989, Friedman and Lemon 1989). However the volume of work performed is an important factor as very high levels of work may take this up to 1.5-1.8kg a day (Brouns et al 1989)
Click To Enlarge.
Endurance Athletes Have A Dramatic Increase
In Enzymatic/Mitochondrial Protein Utilization.
2. Strength Athlete:
With strength athletes there is an opposite need for protein with minimal enzymatic needs but greater structural requirements. Again Tornopolsky et al (1988) showed that strength athletes needed more protein to maintain nitrogen balance than sedentary individuals, with requirements of around 1.2 to 1.7g/kg a day which was supported by others (lemon et al 1990).
Considering these findings the requirements of an athlete could be met with 1.7g/kg each day or for a 70kg athlete around 120g a day, which is easy to consume from a normal diet.
Considering this, why is there so much anecdotal evidence that higher protein intakes result in improved strength and size gains? The problem is in the method of testing. Nitrogen balance just shows the levels required to avoid body protein breakdown - not how much protein is optimal for development. Strength athletes are looking for absolute gains in strength and size - not minimal health requirements.
One of the reasons for strength training is to cause an increase in protein synthesis within the muscles and as noted earlier increasing protein intake causes an increase in protein turnover with increased rates of protein synthesis seen.
For accretion of muscle mass and strength it would seem the double effect of exercise and high protein intake on protein synthesis would lead to the greatest return from the training. This was backed by the work of Dragan et al (1985) who found both increases in strength (5%) and muscle size (6%) when weightlifters increased their protein consumption from 2.2 to 3.5g/kg a day.
In support of this Consolazio et al (1975) witnessed greater nitrogen retention and greater gains in lean mass (3.3kg vs 1.2kg) when protein intake was 2.8g/kg a day instead of 1.4g/kg a day.
The take home message is that protein consumption is a key factor in strength and size adaptations from resistance training and an intake of 1.7g/kg a day rising up to a possible 3.5g/kg during intense microcycles in order to reap maximum gains from resistance training.