Protein is only a minor source of energy during soccer matches (less than 10% of total energy production) and is used primarily for maintaining and building up tissues such as muscles. It is also part of hormones and enzymes, involved in the regulation of energy production and in your general health. As protein is made of 20 Amino Acids (AAs) which are the building blocks of the body, they are too valuable to be used for energy production. However, if the body's carbohydrate levels are low then amino acids can be used for anaerobic processes such as the resynthesis of muscle ATP (provides 4kcals of energy per gram).
Of these 20 amino acids, 8 are essential and but cannot be manufactured by the body and so must be part of our diet. Protein which contains all these essential AAs is is found in foods such as eggs, milk, meat and fish (animal protein). Protein is also found in vegetables and grains (vegetable protein) but is biologically low in value as it contains only a few essential AAs. However vegetarians can get around this by combining several of these food stuffs which are biologically low in value.
It is wrong to think that to develop strength, athletes must consume large quantities of meat for more protein. In actual fact a normal adult needs about 1g of protein per kilogram of body weight per day corresponding to about 70g for a full grown person. According to experts though, children do actually need a higher proportion of protein in their diet to support their growth.
Protein should only make up about 15% of a soccer players diet (slightly over 1g of protein per kilogram of body weight). However, this may be increased during periods of intense training, especially involving muscle strength. In this case, it has been recommended to increase protein intake to 1.5-1.7g of protein per kg of body weight. However, a consequence of eating more meat is the large amount fat it contains. This is especially true for red meat and players should stick to eating leaner meat such as chicken. The table below provides a short list of animal products which are comparatively high and low in fat but contain similar levels of protein.
The type, frequency, and duration of exercise can affect protein requirements. Strength athletes may need more protein due to the degradation of muscle proteins during training whereas evidence shows that in long endurance type events, athletes can spare carbohydrate utilisation and use more protein for energy. Also, cold environments may force the body use more protein for fuel. Finally, athletes recovering from injuries may need to slightly increase their protein intake as when training at high-altitude where they may have to consume up to 2.2 g protein per kg per day.
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