Protein is a complex molecule made up of amino acids.
Proteins are responsible for specific and unique functions within the body. Many people think that we only need protein to build muscle, but, in fact, there are many different proteins that perform many different functions in the body.
Some of the functions of protein are:
- Stores oxygen in muscles
- Involved carrying oxygen around the body via blood
- Involved in muscle contraction
- Helps the body use glucose for energy and regulates blood sugar levels
- Important for transportation of fatty acids
- Involved in the formation of skin and hair
- Forms fibrous connective tissue found in muscles, bone, and cartilage, etc.
- Protection against foreign substances such as bacteria and viruses
The 20 amino acids are:
Alanine, Arginine, Asparagine, Aspartic Acid, Cysteine, Glutamine, Glutamine acid, Glycine, Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Proline, Serine, Threonine, Tyrosine, Tryptophan, Valine.
The body can synthesise the majority of these 20 amino acids. However, 8 of them can’t be built in this way, and so it’s important that these are supplied via food. These eight amino acids are known as essential amino acids and are obtained from various sources of protein in the diet.
From the 20 amino acids, the essential amino acids are:
Histidine, Isoleucine, Threonine, Leucine, Tryptophan, Lysine, Methionine, Valine, Phenylalanine
(Histidine is also an essential amino acid in children and, in some circumstances adults.)
Animal protein can be found in the following:
- Chicken and other white meats
- Red meat
- Dairy products
These proteins are high in essential amino acids in the right proportion and are known as complete proteins. A complete protein is a protein that contains all of the essential amino acids for the dietary needs of humans or other animals.
Plant protein can be found in the following:
- Fruit and vegetables
- Beans and pulses
These proteins are low in essential amino acids and must be eaten in large quantities if you are to gain sufficient levels of amino acids from them. They are known as incomplete proteins. (Incomplete proteins contain protein but are lacking in one or more of the essential amino acids the human body needs.)
Vegetarians and vegans can obtain sufficient protein by knowing what limiting amino acids are contained within various foods, and choose their protein from a variety of different food sources and combining them to obtain the full range of amino acids.
If you consume too little protein this can lead to:
- Poor resistance to infection
- Low energy and stamina levels
- Prolonged recovery from illness.
- Slow healing of wounds
- Mental depression
It is estimated that the average person requires approximately 1g of protein per kilogram of body weight per day. The range given for exercisers around 1.2-1.8g per Kg of body weight for endurance sports and around 2g per Kg of body weight for strength-based sports.
Consuming too much protein:
The upper level of protein intake is 2.5g of protein per Kg of body weight. No benefit is seen from increased intake. The excess protein will not be used unless there is a shortage of energy provided from carbohydrate or fat. It can’t be stored for later use. Excess protein above the bodies’ requirement must be broken down. This is because the nitrogen it contains must be removed from the body.
The nitrogen component of the amino acids is converted to urea and passed out in the urine. The rest of the amino acid not removed as urea, is either used for energy, if necessary or converted into fat and stored. If carbohydrate or fat intakes are too low, the excess protein will be used as energy and not stored as fat.
On a high protein weight loss diet, the energy restriction is achieved through limiting the amount of carbohydrate in the diet (the bodies preferred fuel) and encourages higher intakes of protein. In this situation, the body starts to use the excess protein and body fat stores to make up the energy deficit created by the diet. This is how ‘weight loss’ is achieved. However, as a by-product of this form of energy production, ketone bodies are produced. This forces the body into a state of ketosis. (The body produces Ketones or ketone bodies when it does not receive enough energy from carbohydrate and it uses fat and protein for energy instead.)
One potential side effect of this is the production of ketone bodies, which may increase the acidity of the blood. In an attempt to rectify this, the kidneys ‘leech’ calcium from the bones. As you can imagine, this is not good for long-term bone health, as calcium loss from the bone may lead to the development of osteoporosis or brittle bone disease. Another consequence of excess protein in the diet is an increased strain on the kidneys. This is as a result of the need to remove the nitrogen component of the amino acid from the body. The nitrogen component is converted to urea in the liver and then removed from the body in the urine via the kidneys. Individuals with existing kidney complaints may be particularly at risk