Protein: structure, function and recommended intake

three chickens standing at a window

What are proteins?

Proteins are organic compounds composed of 20 amino acids. Chemically, these are made-up of carbon, hydrogen and oxygen.

Proteins are used in countless bodily processes, not just muscle growth and recovery, but these play a vital role in our body for example; regulating hormones like insulin, growth hormone, IGF-1 are just a few examples (Norton and Baker, 2019). The role proteins play within our body is dependent on the structure that it takes during digestion. 

In this post you will learn what proteins are made up of, their function and the recommended intakes for bodybuilding and weight loss. 

So lets start by explaining their structure first. Proteins are constructed by 20 amino acids; 12 of which are already created within the body and 8 are ‘essential’ meaning we must get them from our diet.

What amino acids make up protein?

The 12 amino acids which are already made naturally within our body include;

  • Alanine
  • Glycine
  • Proline
  • Asparagine
  • Tyrosine
  • Cysteine
  • Glutamine
  • Histidine
  • Arginine
  • Serine
  • Aspartic Acid
  • Glutamic Acid.

The 8 ‘essential’ amino acids include;

  • Histidine
  • Leucine
  • Threonine
  • Methionine
  • Valine
  • Isoleucine
  • Lysine
  • Phenylalanine
  • Tryptophan.

Have you noticed that Histidine is within both of the lists? That’s because in some circumstances it can be an essential amino acid or created by the body.

Which amino acid promotes muscle growth?

The anabolic effect (muscle building & recovery) of the protein seems to be dominated by Leucine meaning that Leucine triggers the muscle protein synthesis (MPS) by stimulating mTOR (mammalian target of rapamycin) which initiates signaling to increase MPS. In simpler terms, Leucine is the one amino acid that drives muscle growth.

So, will you get shredded just by supplementing Leucine? No not really. Supplementation of this amino acid has proven disappointing results as although Leucine stimulates MPS, you would need all the other 19 amino acid for Leucine to have an effect (Norton and Baker, 2019). However, at least now you know which protein shakes are more beneficial for muscle growth, ones with high amounts of Leucine. Whey protein seems to have the biggest % of Leucine compared to other proteins shakes on the market.

Structure of protein

In regards to protein structure, two amino acids can join together to form a dipeptide (‘di’ means two) and the bond that joins these together is called a peptide. When many amino acids join together, they can create a polypeptide (‘poly’ means many), this can involve all of the amino acids.

So how does protein get its shape?

In a polypeptide, the long chain will fold and wrap around itself, there are two forms it can take, either globular or Fibrous, and sometimes both forms. But it is the  structure that will determine its function.

  • Globular proteins form when the polypeptide chain folds itself into a ball-like structure, water soluble (dissolve in a watery environment e.g. blood) and are mainly involved in metabolic processes like transportation and controlling biological processes.
  • Fibrous proteins are long, rod-like fibres and mostly consist of repeated sequences of amino acids which are insoluble in water (do not dissolve in water well. Eg: blood). The fibrous proteins are involved in the creation of connective tissues like tendons and muscle fibres.

Protein types, protein benefits and protein functions:

Role Protein Example Protein Type Function 
Structural a-keratin & Collagen Both Fibrous Involved in skin/ hair formation & Forms connective tissues found in muscles, bones and cartilage  
Contractile Myosin 







Involved in muscle contraction in thick muscle filaments (thread-like fibre) 


Involved in muscle contraction in thick muscle filaments 

Transportation Haemoglobin 


 Serum Albumin 




Carries oxygen around the body through red blood cells 


Found in blood transporting fatty-acids 

Protection Antibodies 






Protects against viruses/ bacteria 


Involved in blood clotting 

Regulation Insulin Globular Helps body use glucose as energy and regulates blood sugar levels 
Storage Myoglobin Globular Stores oxygen in muscles 

This is just a few proteins and their functions. This is just to show you that when you have exercised and you consume a high protein meal, it doesn’t necessarily mean that your body will use all those grams of protein for muscle growth. What that protein does within your body will be determined by its 3D structure. Consuming proteins within 45 minutes after your exercise can increase chances of the proteins taking structure to support muscle growth. Sources of protein include complete proteins and incomplete. Complete proteins mean that they contain all 20 amino acids, whereas incomplete proteins mean that they may contain certain amino acids but not all of them.

Complete protein sources include;

  • red meat
  • chicken
  • white meats
  • Fish
  • dairy products
  • Eggs

Incomplete protein include;

  •  fruit
  •  veg
  •  seeds
  •  beans
  •  pulses

Check out the below infographic on sources of plant protein! Don’t forget to share it with your friends, maybe pin it for later!

How can a high protein diet assist in weight loss?

High protein diets help with maintaining Lean body Mass (lean muscles) which can be beneficial as the more muscles you have the more calories you burn at rest. In other words, say an average person will burn 150-200 calories when they are asleep. If you have muscle, you will burn a lot more depending on how much muscle you have. Per 1lb of muscle you burn roughly around an extra 60 calories per day at rest. Also, proteins have shown to be satiating whilst not being so high in calories. This means you’ll feel full longer without eating many calories. So it may be easier for you to stay within your total daily calories. 

Recommended protein intake.

It is recommended to consume 1g of protein per 1kg of body weight.


In summary, protein is made up of 20 different amino acids and each amino acid has a different role within the body. Although protein is vital for muscle growth, it’s important not to overeat on protein and it can be converted into glucose, and stored as body fat. If you have enjoyed this post, make sure to subscribe to our newsletter to be notified when a new post is uploaded! You will also receive nutrition tips and exclusive offers. you don’t want to miss it.


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Norton, L. and Baker, P. (2019). Fat loss forever. 1st ed

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