PROTEIN THE POWERHOUSE

The importance of protein and the question of whether extra protein is necessary for sports performance is one of the most hotly debated topics among sports scientists, coaches and athletes and has been contended ever since the time of the Ancient Greeks. Protein has long been associated with power and strength, and as the major constituent of muscle, it would seem logical that an increased protein intake would increase muscle size and strength.

Traditionally, scientists have held the view that athletes do not need to consume more than the RDA for protein and that consuming anything greater than this amount would produce no further benefit. However, research since the 1980s has cast doubt on this view. There is considerable evidence that the protein needs of active individuals are consistently higher than those of the general population.

This chapter will help to give you a fuller understanding of the role of protein during exercise, and enable you to work out how much you need. It will show how individual requirements depend on the sport concerned and the training program, and also how they are related to the carbohydrate intake. An example of a daily menu is given to show how to meet your own protein requirements, and to provide a basis for developing your own menu. As more athletes are giving up meat and choosing a vegetarian diet, this chapter explains how you can obtain sufficient protein and other nutrients for peak performance on a meat-free diet.

WHY DO I NEED PROTEIN?

Protein makes up part of the structure of every cell and tissue in your body, including your muscle tissue, internal organs, tendons, skin, hair and nails. On average, it comprises about 20% of your total body weight. Protein is needed for the growth and formation of new tissue, for tissue repair and for regulating many metabolic pathways, and can also be used as fuel for energy production. It is also needed to make almost all of the body enzymes as well as various hormones (such as adrenaline and insulin) and neurotransmitters. Protein has a role in maintaining optimal fluid balance in tissues, transporting nutrients in and out of cells, carrying oxygen and regulating blood clotting.

What are amino acids?

The 20 amino acids are the building blocks of proteins. They can be combined in various ways to form hundreds of different proteins in the body. When you eat protein, it is broken down in your digestive tract into smaller molecular units single amino acids and dipeptides (two amino acids linked together).

Twelve of the amino acids can be made in the body from other amino acids, carbohydrate and nitrogen. These are called dispensable, or non-essential, amino acids (DAAs). The other eight are termed indispensable, or essential, amino acids (IAAs) meaning they must be supplied in the diet. All 20 amino acids are listed in table 3.1. Branched-chain amino acids (BCAAs) include the three IAAs with a branched molecular configuration: valine, leucine and isoleucine. They make up one-third of muscle protein and are a vital substrate for two other amino acids, glutamine and alanine, which are released in large quantities during intense aerobic exercise. Also they can be used directly as fuel by the muscles, particularly when muscle glycogen is depleted. Strictly speaking the bodys requirement is for amino acids rather than protein.

These are then re-assembled into new proteins containing hundreds or even thousands of amino acids linked together.

What types of protein are there?

There are four types of protein commonly used as protein supplements.

1. whey protein
2. casein
3. soy protein
4. egg protein

Whey protein is one of the two major types of protein found in milk (the other is casein). It is formed when milk is curdled (as in cheese manufacture), separating the curd (which contains mainly casein) from the whey (which contains lactalbumin protein, lactose and fat).

Casein is the other major milk protein. It is basically the curd, formed when milk is separated into curds and whey. Low-fat cottage cheese is mostly casein protein together with a little lactose and calcium.

Soy protein is extracted from soybeans.

Egg Protein refers to the proteins found in whole egg.

Protein metabolism

Tissue proteins are continually broken down (catabolised), releasing their constituent amino acids into the free pool, which is located in body tissues and the blood. For example, half of your total body protein is broken down and replaced every 150 days. Amino acids absorbed from food (IAAs) and dispensable amino acids (DAAs) made in the body from nitrogen and carbohydrate can also enter the free pool. Once in the pool, amino acids have four fates. They can be used to build new proteins, they can be oxidised to produce energy and they can be converted in glucose via gluconeogenesis or they can converted into fatty acids. During energy production, the nitrogen part of the protein molecule is excreted in urine, or possibly in sweat.