Daily protein requirement for athletes is one of the more controversial areas of sports nutrition. The issue relates specifically to whether athletes have an increased need for protein compared to sedentary individuals.
Muscle tissue is made from protein, so it is thought that if an athlete consumes a greater amount of protein then they will have greater muscle size and development! Some body builders have been known to consume whole chickens, and eggs by the dozen in an attempt to enhance muscular growth!
According to the IOC, Consensus Conference on Foods, Nutrition and Sports Performance, “Protein requirements are higher in individuals involved in physical training programs than inactive people. However, most athletes already consume sufficient protein as a consequence of their increased energy intakes.” That is, athletes already have an increased energy intake overall, hence their intake of protein will also be increased.
Dietary protein provides the amino acids that are essential to build and repair tissue in the body. There are eight essential amino acids that need to be provided through the diet and twelve non-essential amino acids that the body can produce itself. Animal food sources are classified as complete protein because they provide all the essential and non essential amino acids. Plant food sources are classified as incomplete protein because they do provide some but not all amino acids.
The following table shows the different levels of daily protein requirements for different groups of athletes.
Sedentary adult population0.8 – 1.0g/kg
Recreational athletes1.0 – 1.2g/kg
Endurance athletes1.2 – 1.6g/kg
Football / power sports1.4 – 1.7g/kg
Resistance athletes1.5 – 1.7g/kg (early training) 1.0 – 1.2g.kg (steady state)
Female athletesapprox 15% less than male athletes (due to females being able to spare glycogen more effectively when exercising)
Adolescent athletes (growth spurt)2g/kg
Male athletes consume 1.5 – 4.0g/kg whereas female athletes consume an average of 1.0 – 2.8g/kg.
This shows more than enough protein is being consumed in most cases. Very few athletes consume inadequate levels of protein. Vegans and vegetarians may not consume enough protein if they don’t eat adequate vegetarian alternatives. Some athletes (particularly female) attempting to decrease body weight may also be at risk of not consuming adequate protein.
Why is the Daily Protein Requirement Higher for Athletes?
The daily protein requirement for athletes is higher because protein is used to enhance muscle growth and bulk, and assist the repair of muscle damage. This is especially important in strength based sports. Most of the protein accretion occurs within the first few months of weights training. During this period, the protein required is much greater than that required later.
Protein requirements are also higher because it is used as a fuel in small amounts. This is especially in high intensity training or endurance training of greater than 1 hour, or earlier if muscle glycogen stores are low. The liver and kidneys can synthesise glucose from amino acids (gluconeogenesis). However, consuming more protein than is recommended will not enhance these processes. Extra protein consumed will be merely oxidised and used for energy
Although most athletes consume more protein than they require, some still believe that extra protein (or amino acids) will enhance their performance.”Claims related to these supplements include:
- Improve performance, recovery, power, endurance and energy
- Increase muscle bulk
- Assist weight loss AND weight gain
- Delay fatigue, suppress appetite, control depression
- Stimulate growth hormone release”
(Source: Gold Medal Nutrition, Second Edition, Cardwell, 1999)
There is little scientific evidence supporting the supplement’s benefits in athletes with sufficient protein consumption. It is also important to know that protein is absorbed much more effectively as peptides (i.e. small proteins) rather than as free amino acids. Free amino acids can cause diarrhoea and abdominal pain if consumed excessively.
Branched Chain Amino Acids
Three indispensable amino acids are classified as branched chain due to their chemical structure:
- leucine
- isoleucine
- valine
During exercise, these branched chain amino acids are oxidised in preference to other amino acids. Therefore the theory was suggested that if branched chain amino acids were supplemented in the diet, athletes would be able to exercise longer before fatiguing. This may be true, however, if adequate carbohydrate is stored in the body and fed during exercise, there will only be a small amount of branched chain amino acids oxidised, hence fatigue will be delayed anyway.
Possible Risks of High Protein Intake These include:
- atherogenesis (development of plaque in the arteries near the heart)
- possible impaired kidney function (unlikely unless pre-existing kidney disease)
- accelerated calcium loss
- dehydration (due to excess nitrogen excreted by the kidneys).
Bulking Up
It should be understood that an extremely high protein intake is not the way to increase muscle bulk! Bulking up requires three factors:
- positive energy balance (i.e. a greater energy intake than energy expenditure)
- suitable and specific hypertrophy weights program to stimulate muscular growth
- genetics (i.e. the right parents!!) So from a nutritional point of view, this translates to a high carbohydrate intake to meet energy requirements. Adequate glycogen stores are a must, otherwise body protein will be utilised for energy. There is also need for an adequate protein intake, to ensure muscles continue to repair and grow following exercise. The diet should also include adequate micronutrients for the growth of new tissues (e.g. zinc and iron).
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