Proteins

During the process of digestion, the proteins in our food are broken down into their constituent amino acids that are in turn 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 4 Calories. Many proteins function as enzymes and others:

Form the structural framework of various parts of the body - Keratin in skin and hair
Function as hormones - Insulin
Serve as antibodies
Transport vital substances throughout the body - hemoglobin
Serve as contractile elements in muscle tissues - actin & myosin

Amino Acids

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 8 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. Non-essential amino acids can be synthesized by body but this does not mean they are unimportant, they are, it is just that the body is capable of producing sufficient to meet the demands for growth and tissue repair. It is therefore important that our diet contain appropriate levels of protein.

The essential Amino Acids (Bean 1993)^[1] are: lsoleucine, Leucine, Lysine, Methionine, Phenylaianine, Threonine, Tryptophan and Valine.

The non-essential Amino Acids (Bean 1993)^[1] are: Alanine, Arginine, Asparagine, Aspartic acid, Cysteine, Clutamic acid, Clutamine, Glycine, Histidine*, Proline, Serine and Tyrosine.

* Histidine is essential for babies but not for adults.

Recommended Protein Intake

Despite the beliefs of many coaches and athletes, eating excessive protein provides little benefit. Muscle mass does not increase simply 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 through the production and elimination of urea and other solutes.

The recommended daily allowance for men and women (McArdle et al. 2000)^[2]:

Adolescent - 0.9 grm of protein per kg body weight
Adult - 0.8 grm of protein per kg body weight

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 greater your protein breakdown will be, and the greater your needs will become. If you train to increase muscle mass, your protein needs will be greater still. Extra protein will be needed not only to compensate for protein breakdown but also for new protein to be made and for muscle growth. It is important to realise that a high-protein diet alone will not lead to any increase in strength or muscle size. It is only when it is combined with heavy resistance exercise that additional protein can cause this to happen.

Research over the past 10 years has indicated that athletes engaged in intense training need to ingest 1.5 to 2 times the recommended intake in order 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 both impact on nitrogen balance; and there are a number of 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 simply 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), and tends to undergo breakdown during periods of high-energy demand, when carbohydrate and/or the amino acid pool becomes depleted. Furthermore, carbohydrates stimulate the release of insulin, a highly anabolic hormone, which helps to drive both glucose and amino acids into muscle cells. Any athlete seeking to optimise his or her protein metabolism should therefore ensure a carbohydrate intake commensurate with training volume.

The following are some steps you can take to optimise your protein nutrition:

Ensure an adequate intake of dietary protein - i.e. a minimum of 1.5g of high-quality protein per kg of body weight per day. Power/strength athletes, or those engaged in intense training, should consider increasing this to 2g/kg/day
Ingest protein carbohydrate drinks after exercise rather than protein alone. Ideally, consume a drink made up of about 1g per kg of carbohydrate and 0.5g per kg of protein within 30 minutes of training, and eat a high-carbohydrate meal within two hours
Consume a light pre-exercise snack: 50g of carbohydrate and 5-10g of protein taken before a training session can increase carbohydrate availability towards the end of an intense exercise bout and also increase the availability of amino acids to muscles. However, make sure your snacks are low in fat to allow for rapid gastric emptying
Use protein/carbohydrate drinks during very long events: a solution containing 73g carbohydrate and 18g protein per litre, consumed at a rate of 1ml per kg of body weight per minute, may delay the onset of fatigue and reduce muscle damage
Consume quick-digesting proteins such as soy and whey immediately after training: this may be especially important for older athletes
At other meals, consume a mix of proteins in order to promote a more sustained release of amino acids into the body
Adding branched chain amino acids (BCAAs) to your normal protein intake may be useful for athletes undergoing prolonged or heavy training, and this may be particularly true for events/sports requiring large amounts of mental agility and motor coordination
HMB supplementation, at 3g per day, may be a useful additional strategy for novice athletes, or those returning to training after a layoff (HMB is a leucine metabolite)
Ensure that your overall diet is of high quality and as whole and unprocessed as possible: this will ensure adequate intakes of other nutrients essential for protein metabolism, such as zinc and B vitamins

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 that are derived from animals: meat, fish, eggs, milk and dairy products

Referenced Material

BEAN, A (1993) The complete guide to Sports Nutrition. 1st ed. London:A & C Black
McARDLE, W.D. et al. (2000) Training muscles to become stronger. In: McARDLE, W.D. et al., 2nd ed. Essentials of Exercise Physiology, USA: Lippincott Williams and Wilkins, p. 56

Page Reference

The reference for this page is:

MACKENZIE, B. (2001) Proteins [WWW] Available from: http://www.brianmac.co.uk/protein.htm [Accessed

Associated Pages

The following Sports Coach pages should be read in conjunction with this page: