Proteins are essential to support life. 

They’re composed of the chemical elements - carbon, hydrogen, oxygen and nitrogen.        Some also contain minerals - such as - zinc, sulphur, iron or potassium. 

The word protein comes from the Greek word - Proteios - which means of primary importance.

Indeed – proteins are vitally important - in that – they’re the only nutrient to supply the body with nitrogen. 

Protein is a vital molecule that carries out many functions in your body including:

  • Repair of old damaged muscle proteins and remodelling of new functional muscle proteins.
  • Structure – for example – collagen and keratin that can be found in our nails and hair.
  • Transport of substances across cell membranes - blood transport proteins that move certain substances – such as - iron, oxygen and cholesterol - throughout our bodies.
  • Hormones – which send chemical signals. Some hormones consist of as little as a single amino acid.        Others are peptides or polypeptides – for example – insulin.
  • And - Contraction: of muscle fibres.

A key component of the muscle remodelling process is muscle protein synthesis - the synthesis of amino acids into functional contractile myofibrillar proteins and energy producing mitochondrial proteins.       

According to researchers from the University of Stirling - a number of factors including the source per meal dose, daytime pattern and timing in relation to exercise - of ingested protein - as well as - co-ingestion of other nutrients - all influence the response of MPS to protein intake.

Let’s look at proteins in a little more detail.       Proteins are large biological molecules made of amino acids - which are joined together by peptide bonds. 

Amino acids represent the simpler units that make up proteins - and – it’s to these units that they’re broken down and digested within the gut. 

There are 20 amino acids that we know about.         And different foods contain different amounts and combinations of these amino acids.

Amino acids are classed as either - essential or non-essential - depending on whether the body is able to manufacture them or not. 

There are eight amino acids which the body is unable to make for itself.        These are classed as essential amino acids - essential meaning that they are a necessary part of our diet. 

The remaining amino acids are termed non-essential - which means the body is able to synthesise these and they are – therefore - not an essential component of our diet.

So – what’s the primary function of protein?        Its main role is to build and repair body tissue.

It can also be used as a secondary source of energy - when carbohydrate and fat supplies are limited – and - as such - proteins have an energy value of four calories per gram. 

The body is unable to store excess protein and – therefore - a constant daily supply is required in the diet.

However - when protein intake exceeds requirements - the excess amino acids are broken down - the nitrogen element is excreted - and the rest of the molecule is used to provide energy immediately or is converted to fat or carbohydrate and stored. 

Here’s an interesting fact for you - protein is known to be the most satiating macronutrient - meaning they help you feel fuller for longer – more so than fat or carbohydrates. 

A prime example of protein’s satiating effect was witnessed in a study which showed that -when we eat whenever we feel like it rather than following a routine - increasing protein intake from 15 to 30 percent of total energy resulted in a spontaneous drop in energy intake by 441 kilocalories per day.        This led to a body weight decrease of 4.9 kilograms in 12 weeks. 

We don’t yet fully understand the physiological processes of the satiating effect of protein-rich diets - however - according to Dr Alexandra Johnstone – a leading protein researcher from the University of Aberdeen – the possible mechanisms include:

  • Protein’s cause the release of gut hormones - which promote the feeling of fullness or reduce feelings of hunger.
  • Protein’s slows the rate of passage through the small intestine - which gives a physical sense of fullness.
  • The role of the liver in metabolite production from amino acids which can be linked - via the vagal nerve - to the brain’s sense of hunger.
  • And - Direct action of amino acids in the brain - entering via across the blood brain barrier.

Another fact you might find interesting - is that – protein has the highest thermic effect - and is the most metabolically expensive.        Taking this into consideration – it’s not surprising higher protein intakes have been seen to preserve resting energy expenditure while dieting.

Protein foods - just like carbohydrate foods - are classified into two groups.         And -the value of foods for meeting protein needs - is determined by their composition of essential amino acids. 

Foods containing all the essential amino acids - are considered to have a high biological value - and may be termed first class or complete proteins - which tend to be animal foods but include soya. 

Foods limited in their supply of one or more of the essential amino acids - are considered to have a low biological value - and may be termed second class - or incomplete proteins - which are of vegetable origin.

When protein foods are eaten – they’re broken down to the constituent amino acids during digestion - absorbed - and then reformed into the proteins required by the body.

If you look at this table – it shows which protein foods have high and low biological values.



High Biological Value

meat, poultry, offal

fish, eggs, milk, cheese

yoghurt, soya

Low Biological Value

cereals, bread, rice

pasta, pulses, peas,

beans, lentils, nuts



In protein rich foods – we can find 10g protein in

  • 2 small eggs
  • 300 ml cow’s milk
  • 20g skim milk powder
  • 30g cheese
  • 200g yoghurt
  • 35 - 50g meat, fish or chicken
  • 4 slices bread – 90g breakfast cereal
  • 2 cups cooked pasta or 3 cups rice
  • 400 ml soy milk – 60g nuts or seeds
  • 120g tofu or soy meat – 150g legumes or lentils
  • 200g baked beans – 150 ml fruit smoothie or liquid meal supplement

 In our next blog we will cover 1. how much protein you actually need per day and 2. the best sources of protein you should consume. 





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