During digestion, the proteins in our food are broken down into their constituent amino acids that are 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 four Calories. Many proteins function as enzymes and others:
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 eight are referred to as essential amino acids which cannot be synthesized by the human body. Animals and plants manufacture proteins that contain these essential amino acids. The body can synthesize non-essential amino acids, but this does not mean they are unimportant. It is just that the body can produce sufficient to meet the demands for growth and tissue repair. Therefore, our diet must contain appropriate levels of protein.
The essential Amino Acids (Bean 1993) are Histidine, lsoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan and Valine.
The non-essential Amino Acids (Bean 1993) are Alanine, Arginine, Asparagine, Aspartic acid, Cysteine, Glutamic acid, Glutamine, Glycine, Proline, Serine and Tyrosine.
Recommended Protein Intake
Despite many coaches and athletes' beliefs, eating excessive protein provides little benefit. Muscle mass does not increase by eating high protein foods. Protein intake significantly above the recommended values can prove harmful because excessive protein breakdown strains the liver and kidney functions by producing and eliminating urea and other solutes.
The recommended daily allowance for men and women (McArdle et al. 2000):
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 higher your protein breakdown will be, and the higher your needs will become. If you train to increase muscle mass, your protein needs will be greater still. The extra protein will be needed to compensate for protein breakdown and for a new protein to be made and for muscle growth. It is essential to realise that a high-protein diet alone will not increase strength or muscle size. It is only when combined with heavy resistance exercise that additional protein can cause this to happen.
Over the past ten years, research has indicated that athletes engaged in intense training need to ingest 1.5 to 2 times the recommended intake to maintain a positive protein balance. Bear in mind that excess protein is converted to fat and stored.
Optimum Protein Nutrition
There is more to protein nutrition than just eating the optimum amount; the timing of consumption and the type of protein selected can impact nitrogen balance, and there are many nutritional 'co-factors' that are either essential or useful in promoting optimum protein metabolism within the body. This is especially true where carbohydrate is concerned because building or even maintaining lean tissue mass is an 'energy-intensive' process.
Increasing protein intake at the expense of carbohydrate can be a bad strategy for athletes engaged in heavy training because without sufficient carbohydrate the body switches to other fuels for energy, and amino acids from protein (particularly the branched-chain amino acids, leucine, isoleucine and valine) provide a ready source of energy!
Muscle tissue is a relatively rich source of branched-chain amino acids (BCAAs). It tends to undergo breakdown during periods of high-energy demand when carbohydrate and/or the amino acid pool becomes depleted. Furthermore, carbohydrates stimulate insulin release, a highly anabolic hormone, which helps to drive both glucose and amino acids into muscle cells. Any athlete seeking to optimise their protein metabolism should ensure a carbohydrate intake commensurate with training volume.
The following are some steps you can take to optimise your protein nutrition:
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 derived from animals: meat, fish, eggs, milk and dairy products.
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