The role of protein and recommended intake
The role of protein
Protein is a macronutrient that helps with the repair of cells. It contains four calories per gram. Although personal trainers may have clients who have a high protein intake in order to repair muscles after training, every cell in the body needs protein for regeneration, from muscle and bone cells to skin and hair cells. Our bodies primarily use glucose and fat as fuel; protein is only rarely used, in cases where a person is in a very fasted state.
Protein can be categorised into:
Essential amino acids (9) – these can’t be synthesized by the body and so need to be taken in as food on a daily basis;
Non-essential amino acids (11) – these can be synthesized by our body from the essential amino acids we have taken in. However, it’s a good idea to also take in non-essential amino acids through our food to save our bodies from needing to produce them.
Amino acids are made up of peptides in the following quantities:
Dipeptides = two peptides together
Tripeptides = three peptides
Oligopeptides = four to nine peptides
Polypeptides = 10 or more peptides
Good sources of essential amino acids
A fitness instructor will recommend that a client consumes proteins that are a good source of essential amino acids. These include: any kind of fish or meat, eggs, dairy, soy-based foods and tofu.
When choosing sources of protein, it’s best to go for good-quality, fresh, organic foods. A free-range, corn-fed chicken, carefully prepared by a butcher will provide a better source of protein than a cheaper quality chicken, which has been fed on inferior food and may have had water injected into it so that it weighs a lot more when bought than it does after cooking.
The most important amino acids for promoting protein synthesis are isoleucine and leucine. Food products/protein supplements that say they contain all essential amino acids or branched-chain amino acids will contain the above, as well as additional essential amino acids.
Recommended guidelines for protein intake
The more active a personal trainer’s clients are, the more protein they will need to repair their muscle fibres.
Sedentary person: 0.8 – 1g of protein for every kg of body weight
Active person: 1.0 – 1.4g of protein for every kg of body weight
Very active/sportsperson: 1.5 – 1.8g of protein for every kg of body weight
Also, if a sedentary person starts to exercise on a regular basis, they will need to increase their protein intake, as the amount of adaptation that their body will go through will be significantly higher than the amount of adaptation that would occur with an active person who is used to exercise. As the sedentary person gets used to exercise and there’s less damage to their muscles, they can decrease their protein intake accordingly.
Frequency of protein intake
Generally, protein should be consumed every two to three hours, to ensure that the protein breakdown (degeneration of muscle fibre, skin cells etc) is slower than protein synthesis. In other words, our bodies need to have access to amino acids to regenerate and repair cells (known as an amino acid pull) faster than the rate they are broken down.
Can we have too much protein?
Research has shown that too much protein can put stress on the liver and kidneys. It has also been found that protein synthesis will plateau at around 2g per kg of body weight. As the body is not able to process protein above this amount, there will be no additional benefit from ingesting the additional protein and it may cause the person to put on weight.
The bioavailability of a protein is the amount that your body can ingest and utilise. For example, the bioavailability of beans is 50%, so if someone were to eat a quantity of beans containing 20g of protein, they would only absorb and benefit from 10g of protein.
Other bioavailability percentages:
Cow’s milk: 91%
At the same time, it’s important to be aware that specific foodstuffs may not contain all of the 9 essential amino acids (eg. broccoli, carrots etc). These types of food are called incomplete proteins. Although they don’t contain all the essential amino acids required they are still beneficial to the diet due to their vitamin and mineral content. In addition these foods can complement each other so together they will supply all 9 of the essential amino acids.