Protein is a key nutritional component for successful athletic performance. Protein has been a long researched nutrient and its roles are well understood. After water, protein is the second largest component of the body with the average adult body containing 10-12kg. It is stored in 3 places within the body; the muscles, liver and blood plasma.
Protein is found throughout the body in hair, nails, outer layers of skin, muscle tissue, the inner structure of bones, and red blood cells. Protein is used by the body to perform many structural, mechanical and cellular functions in the body including:
- Immune Responses
- Manufacture and repair of muscle tissues
- Production of enzymes
- Transport and storage of nutrients
- Hormone production
- Cell manufacture and functioning
- Maintaining fluid balance
- Transporting oxygen throughout the body
- Source of energy
Proteins are made of sequences of amino acids known as ‘the building blocks’ of the body. Every protein has its own unique sequence and number of amino acids, which determines its particular structure and function. There are 20 amino acids, of which 12 are non essential and synthesised by the body, and 8 are essential and cannot be synthesised by the body; these must be taken in through the diet.
The eight essential amino acids required by humans are: leucine, isoleucine, valine, threonine, methionine, phenylalanine, tryptophan, and lysine. Histidine is also considered to be an essential amino acid for children.
COMPLETE AND INCOMPLETE PROTEINS
The quality of a protein is dependent on its presence of amino acids. For this reason proteins are categorised into complete and incomplete proteins. Complete proteins are those which contain all eight essential amino acids. They contain the correct ratio of amino acids to maintain protein balance and allow tissue growth and repair. Incomplete proteins do not contain all eight essential amino acids.
Proteins derived from animals that are classed as high quality and complete proteins as they contain ample amounts of essential amino acids required by the body. Sources of complete proteins include poultry, meat, fish, eggs, milk and cheese.
Proteins derived from plants are often classed as incomplete proteins as they do not contain all essential amino acids. Examples include fruits, vegetables, nuts, seeds, beans, grains, cereals, legumes and soy foods. These proteins are still good sources of protein particularly for vegan or vegetarian athletes. Some plant proteins can be combined to make complete proteins for example rice and beans. In other cases nutritional protein supplements such as whey protein powders or protein bars may be an alternative option particularly for convenience or if foods are too impractical or heavy for athletes.
PROTEIN IN THE DIET
Although there is much research and understanding around the role of protein, controversy and mixed information still exists concerning how much an athlete should take within their diet. Percentage guidelines are no longer used, with recommendations provided as grams per kilogram body weight. Sedentary requirements are estimated at 0.8 g/kg/body mass per day, whilst those exercising range from 1.2-2.2 g/kg/BM/day. Protein is prevalent in the diet in terms of the volume, but it is the timing of protein intake which is important.
PROTEIN FOR RECOVERY AND TIMING OF PROTEIN INGESTION
Timing of protein consumption is pivotal for athletes whether the goal is to induce muscle mass, strength or recover after exercise. High-intensity resistance exercise is key to stimulate muscle growth and strength, by stimulating protein synthesis, which can last for up to 72 h after exercise. However, protein breakdown also increases post-exercise, and it can exceed protein synthesis in the absence of food intake. There is evidence that protein should be taken within one hour following exercise if muscle growth stimulation is the main objective. 20-25 g of good quality protein (providing ~8.5-10 g of essential amino acids), consumed at the end of resistance exercise, is recommended to stimulate near-maximal muscle protein synthesis, for high muscle growth effects.
For endurance athletes there are often myths around the athlete not needing to consume protein for their performance as it may lead to unwanted muscle mass gains. This is untrue as endurance athletes in heavy training require extra protein to cover a small proportion of the energy costs of their training, and to assist in the repair and recovery process of the muscles after exercise. Again, the consumption of 20-25g of protein consumed within the first 60 minutes following exercise is advised to rapidly achieve the high rates of protein synthesis necessary to minimise muscle cell degradation.