Senin, Februari 19, 2007


Proteins are the basic structure of all living cells. Proteins are used in making hormones, blood plasma transport systems, and enzymes. The basic building blocks of proteins are called amino acids. There are two types of proteins complete and incomplete. Amino acids are categorized as essential and non-essential. Of the twenty amino acids that have been identified, nine are considered essential amino acids those that are not manufactured by the body, these must come from dietary intake. The body can manufacture the non-essential amino acids from the by-products of carbohydrate metabolism. Other protein comes from the recycling of enzymes and other proteins. Protein is synthesized in all tissues in the body, however, the liver and muscles are the most active. The body synthesizes about 300 grams of protein per day even though average intake is only 70 grams.
Proteins that contain all nine essential amino acids in sufficient quantity to sustain life are called complete proteins. Meat, fish, milk, cheese and eggs contain complete proteins. Incomplete proteins such as vegetables, grains, seeds, and nuts are those which do not contain all nine essential amino acids by themselves. However, combinations of incomplete protein foods can supply all nine essential amino acids such as beans with rice or peanut butter on wheat bread. Therefore vegetarians can get all the amino acids required by combining incomplete protein foods.
Examples of Protein rich foods:
· High Fat ‑ Meat, salmon, eggs, peanut butter, milk, cheese
· Low Fat ‑ Tuna, egg whites, red beans, skim milk, non‑fat cheese
Proteins begin digestion in the stomach but are primarily digested in the small intestine and metabolized by the liver for the building of tissue. Proteins that are not required for building can be utilized as an energy source and provide 4 calories per gram. About 98% of the protein from animal sources and about 80% of the protein from vegetable sources is absorbed by the body.
Fasting causes the body to use protein as an energy source even to the point of breaking down vital tissues such as organs and muscles to use as an energy source. Excess protein, not utilized for tissue repair or growth or as an energy source is converted by the body to fat and stored.
Protein requirements depend on the individual and daily activity. Tissue growth, whether due to growth, injury, weight training, pregnancy effect protein requirements. During illness, protein is not only required for repair but is generally used as an energy source. According to RDA requirements, an adult should consume approximately 0.36 grams of protein per pound of body weight on a daily basis. As an example, a 150 pound person should consume approximately 50 grams of protein daily. This translates to 200 calories of protein daily. As a general rule, for intense weight training, up to 1 gram per pound of body weight may be consumed.
Since protein metabolism produces nitrogen in the body this creates an extra work load for the kidneys and liver to eliminate the excess. Dehydration can occur because the kidneys require increased amounts of water to dilute the nitrogen. Dehydration can impede workout performance. It's therefore important to adequately hydrate when consuming increased levels of protein.
source : Training Manual & Certification Course, Fitness ABCs
written by Chuck Krautblatt, Personal Trainer and Aerobics Instructor
1995, 1998

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