Protein is made up of amino acids linked by peptide bonds. A typical protein may consist of 300 amino acids. During the process of digestion the proteins in our food are broken down into their constituent amino acids which are in turn absorbed by the blood capillaries and transported to the liver. The amino acids are then synthesized into proteins or stored as fat or glycogen for energy. Each gram of protein produces approximately 4 kcal. Many proteins function as enzymes. Other proteins form the structural framework of various parts of the body (eg: Keratin in skin and hair), function as hormones (eg: Insulin), serve as antibodies, transport vital substances throughout the body (eg: hemoglobin) and serve as contractile elements in muscle tissues (eg: actin & myosin).
 
Amino Acids
Amino acids are the building blocks of protein. The formation of protein can result in dehydration because water molecules are lost as amino acids combine to form more complex molecules.
The body requires 20 different amino acids of which 8 are referred to as essential amino acids which cannot be synthesized by the human body. Animals and plants manufacture proteins which contain these essential amino acids. Non-essential amino acids can be synthesized by body but this does not mean they are unimportant, they are, it is just that the body is capable of producing sufficient to meet the demands for growth and tissue repair. It is therefore important that our diet contains appropriate levels of protein.
The essential Amino Acids are: Isoleucine, Leucine, Lysine, Methionine, Phenylaianine, Threonine, Tryptophan and Valine.
The non-essential Amino Acids are: Alanine, Arginine, Asparagine, Aspartic acid, Cysteine, Clutamic acid, Clutamine, Glycine, Histidine*, Proline, Serine and Tyrosine.
* Histidine is essential for babies but not for adults.
To read more about amino acids click here
 
Recommended Protein Intake
Despite the beliefs of many coaches and athletes, eating excessive protein provides little benefit. For athletes, muscle mass does not increase simply by eating high protein foods. Protein intake that is significantly above the recommended levels can prove harmful. Excessive protein breakdown strains the liver and kidney functions through the production and elimination of urea and other solutes.
The recommended daily allowance of protein for men and women is:
Adolescent – 0.9 grm of protein per kg body weight
Adult – 0.8 grm of protein per kg body weight
Training and Protein Needs
Research suggests that protein breakdown increases during and immediately after exercise, and that protein manufacture slows down at the same time. The more intense the exercise, the greater your protein breakdown will be, and the greater your needs will become. If you train to increase muscle mass, your protein needs will be greater still. Extra protein will be needed not only to compensate for protein breakdown but also for new protein to be made and for muscle growth. It is important to realise that a high-protein diet alone will not lead to any increase in strength or muscle size. It is only when it is combined with heavy resistance exercise that additional protein can cause this to happen.
Energy Provision
Proteins have a relatively minor (compared to carbohydrate and water) role in the provision of energy.
Recovery
Proteins have a bigger role in the recovery period post exercise. The key challenge post exercise (other than rehydrating) is to replenish the body’s glycogen reserves as fast as possible. The mechanism is to feed carbohydrate, which enters the blood and stimulates the release of insulin, which triggers the body to convert the blood glucose from the carbohydrate to glycogen.
Recent scientific studies have shown that the addition of proteins to drinks in this recovery phase can increase the release of insulin, and speed up the re-building of liver and muscle glycogen.
Recovery Time
Protein only (25 gram/hour) 78 hours
Carbo 2 hours after exercise
(60 grams/hour) 37 hours
Carbo straight after exercise (60g/hr) 23 hours
Carbo plus Protein (25g + 60g) 18 hours
Carbo Plus Peptides (25g + 60g) 16 hours
Source of Protein
Proteins that contain all the essential amino acids in approximately the right proportions for your body’s requirements are sometimes called ‘high-biological-value’ proteins. These are found in foods that are derived from animals (eg: meat, fish, eggs, milk and dairy products).