Protein works in your body to grow, repair, and replace tissues.
The proteins that you eat - in meat and fish and eggs, in dairy products and nuts, and vegetables such as beans - are broken down in the stomach during digestion by enzymes known as proteases, into smaller polypeptides to provide amino acids for the body. Along with their role in protein synthesis, amino acids are also important nutritional sources of nitrogen.
For body builders, nitrogen balance is an important notion to remember when talking about protein intake. Nitrogen balance is the difference between the amount of nitrogen taken in and the amount excreted or lost. If you consume more than you lose, you achieve an anabolic - or muscle building - state, when your body has a positive nitrogen balance. This is what you want.
If, however, your protein output exceeds intake you have a negative nitrogen balance, which is not good because your body loses muscle mass. This puts your body in what is called a catabolic state, which is when muscle tissue is broken down for energy purposes. Your body can't grow when it's in a catabolic state.
The general rule is to consume each day the same amount of grammes in protein as your body weighs in kilos. A 150 lb/ 70 kg body builder, therefore, would need to eat 70 grammes of protein every day to maintain an anabolic state. When calculating the amount of protein you eat, concentrate on the complete sources of protein like meat, fish, and eggs.
Some people don't feel that loading up on protein is a good idea for anyone. Vegetarians would argue that one of the health benefits of a vegetarian diet is that it contains adequate but not excessive protein. They also claim that the amino acids missing from the relatively low grade protein available from plants can be had by simply combining different types of plant proteins. Anti-Atkins types point at the lack of fibre in a high protein diet, and potential problems with high cholesterol.
But if you want to get in good shape, you need the amino acids in protein to work in your body. Bottom line? When you work out, eat a normal diet containing healthy animal sources of protein - lean red meat, chicken and fish - and eat a little more on your workout days and when resting. If you don't have chronic kidney disease, don't worry about your protein intake.
