Proteins, carbohydrates, and fats are the three food groups that comprise the human diet. For a healthy and active person, with no specialized dietary needs, protein should be approximately 12-15% of the total food consumed every day. The ingestion of proteins, both in terms of the timing and the quantity consumed, is critical to an athlete's quick and efficient recovery from the stresses imposed on the body by exercise.
The ingestion of proteins is the first step in the conversion of these foods into a form that the body can utilize. Ingestion is the act of physically consuming food; digestion is the conversion of the food to a form that the body can assimilate and absorb; and synthesis is the process of using the absorbed protein to create a functional substance. The key components of proteins are various amino acids, which are the building blocks for the construction and repair of muscles within the body. Protein is also an essential aspect of the ability of the nervous system to transmit impulses. They are also a part of the chemistry of many hormones secreted by the endocrine system and are essential to the functioning of the immune system.
The ingestion of dietary proteins is important to the health of the skeletal muscles, one of the three different types of muscle in the body. The other muscle types, the cardiac muscles that power the heart and the smooth muscles that work within the interior portions of many of the internal organs, are maintained and restored by other internal means.
A healthy athlete should consume protein in the diet on a relatively steady basis throughout the day. Steady consumption usually ensures an equally steady and continuous protein synthesis. All forms of exercise will place demands on the body that deplete the levels of proteins and their constituent amino acids; the intensity of exercise, particularly resistance exercises such as weight training and other explosive movements, will have a correspondingly greater effect in the reduction of protein levels. Muscles cannot grow in either mass or strength unless they are stressed and then provided the opportunity to be repaired. As a very general guideline to how much protein a healthy person should consume on a daily basis, one gram of protein per pound (0.5 kg) of lean body weight (the total body weight less body fat) is an accepted figure.
A blood test can assist in determining precisely how much protein should be consumed by a specific athlete. The blood urea nitrogen test is a measurement of the amount of urea on the blood. Nitrogen is one of the elements present in all forms of protein; nitrogen will exist in its elemental state as a byproduct of protein breakdown. Urea is also a byproduct of protein synthesis, in which excess proteins will lead to the generation of excess amino acids that must be broken down and processed by the liver for ultimate excretion from the body by the kidneys as urine. If protein consumption is too high for the body to use in the synthesis process, this fact is revealed through an elevated urea level. Long-term excess protein consumption may place significant stress on the liver and kidney functions.
Amino acids made available to the body from digested protein also require significant amounts of water to become metabolized in the liver; amino acid molecules require twice as much water to be broken down as does a glucose molecule. High protein consumption can easily lead to dehydration for this reason.
When the amount of protein consumed into the body is too low to meet the needs of repair and restoration of muscles, these tissues will ultimately break down, without any corresponding build up. This process, known as muscle catabolism, is dangerous to the long-term health of the musculoskeletal system, as the body does not have an alternative means with which to sustain these structures.
Research studies with respect to the optimum timing of protein replacement suggest that proteins should be ingested between 30 minutes and one hour after the muscle resistance or other strenuous activity. It is generally agreed that a series of smaller meals, each with a protein component, will be digested more agreeably by the body than one large meal. A number of amino acids necessary to human function must be obtained through food, and certain types of foods are superior protein sources in this regard: eggs, most fish, milk, and other dairy products are known as complete protein sources for this reason. Incomplete or complementary proteins are found in beans, nuts, and many vegetables.