Proteins belong to a family of organic compounds that serve many functions in the body. All proteins are made from building blocks called amino acids, and there are 20 of these in total.
The basic structure of protein is a chain of amino acids. Amino acids can be thought of as forming a ‘protein alphabet’. They build proteins in a similar way to how the 26 letters of the alphabet are used in various combinations to create individual words – one protein will differ from another according to the number and sequence of its constituent amino acids. Most proteins are relatively large molecules comprised of at least 100 amino acids. Smaller clusters of amino acids are referred to as peptides.
Proteins are the building blocks of life. The body needs protein to repair and maintain itself. Every cell in the human body contains protein. It is a chief component of the skin, muscles, organs and glands. Protein is also found in all body fluids, except bile and urine. Protein is needed in the diet to help the body repair cells and make new ones. The nutrient is also important for growth and development during childhood, adolescence and pregnancy. When proteins are digested, amino acids are left. The human body needs a number of amino acids to break down food. Amino acids need to be eaten in large enough amounts for optimal health.
Amino acids are found in animal sources (e.g. meat, fish and eggs), plant sources (e.g. soy beans, legumes, nut butters) and some grains (e.g. wheat germ). We do not have to eat animal products to get all the protein our bodies require.
Essential Amino Acids
Of the 20 amino acids, 9 are considered to be essential to the daily diet because the body is unable to produce or synthesise them itself. Only when sufficient quantities of these amino acids have been ingested are we able to synthesise the remaining nonessential amino acids.
Non-Essential Amino Acids
These are made by the body from essential amino acids or in the normal breakdown of proteins. They are also present in many foods but are not always required to be part of the daily diet.
Conditionally Essential Amino Acids
These are also present in many foods but are not always required to be a part of the daily diet. So long as we successfully absorb sufficient amounts of the nine essential amino acids, the liver is able to synthesise the remaining conditionally essential amino acids. However, at certain times in life and in certain population groups, these amino acids must be supplied by the diet to ensure good health. An adequate intake of the conditionally essential amino acids will also help to protect valuable reserves of the essential amino acids.
Sources of protein
Sources of protein include:
• Turkey and chicken with skin removed.
• Lean cuts of beef or pork (visible fat trimmed).
• Fish or shellfish.
• Pinto beans, black beans, kidney beans, lentils, split peas
and garbanzo beans.
• Nuts and seeds, including almonds, hazelnuts, mixed nuts,
peanuts, peanut butter, sunflower seeds and walnuts.
• Tofu, tempeh and other soy protein products.
• Low-fat dairy products.
A nutritionally balanced diet provides the body with enough protein, so healthy people rarely need protein supplements. The amount of recommended daily protein depends on your age and health. Two to three servings of protein-rich food will meet the daily needs of most adults.
Protein requirements can be met by consuming complete, incomplete and complementary proteins.
These foods contain all nine essential amino acids in sufficient amounts necessary for the liver to synthesise the remaining non-essential amino acids. Most of these are animal-based foods. Some experts claim that there are a number of plant-based complete proteins, but the density of essential amino acids is generally higher in animal-based proteins.
Plants also contain protein, however these proteins are considered to have a lower biological value since they are usually lacking one or more of the essential amino acids. Plants also generally contain smaller concentrations of protein, making it difficult to ingest enough solely from plant produce.
Some sources of incomplete proteins:
• Cereals and grains (wheat, rye, barley, oats, rice).
• Cereal products (bread, pasta).
• Pulses (beans, lentils, peas).
For many years nutritionists have advised vegetarians to vary or combine
plant-based protein sources to boost amino acid intake. This may help to provide a full spectrum of the essential amino acids in the diet. Whilst these carbohydrate-based foods contain energy in the form of glucose, it is important to remember that they also contain smaller amounts of protein. This means that including a variety of unrefined carbohydrate foods is particularly important for anyone on a no-animal protein or low animal protein diet.
Appropriate variations or combinations include:
• Rice and pulses.
• Vegetables and seeds.
• Nuts and vegetables.
• Grains and pulses.
The Functions of Protein
• They serve as enzymatic catalysts.
• They are used as transport molecules (haemoglobin transports oxygen) and storage molecules (iron is stored in the liver as a complex with the protein ferritin).
• They are used in movement (proteins are the major component of muscles).
• They are needed for mechanical support (skin and bone contain collagen, which is a fibrous protein).
• They mediate cell responses (rhodopsin is a protein in the eye which is used for vision).
• Antibody proteins are needed for immune protection.
The amount of protein required for effective function will vary significantly from person to person. It’s very difficult to get it right with a simple calculation, and it takes some trial and error and fine-tuning to find what works best for an individual.
In the UK it is often the case that the only decent amount of protein eaten during the day is in the evening meal. Protein should be a major part of every meal consumed. A basic starting point to work out how much protein an individual needs is to consider body weight and physical activity levels.
We hope you found this article helpful but if you have any questions, please do get in touch.
The Fitness Focus Team
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