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What is protein?

31st July 19 - 9 minute read

Headshot of James Hudson

Performance Nutritionist at Nutrition in Sport

Our expert:
James Hudson, Performance Nutritionist at Nutrition in Sport. James played Premiership Rugby for Gloucester, as well as lining up for London Irish, Newcastle Falcons and England Saxons. He has a degree and masters in biochemistry from the University of Bath and has completed the International Olympic Committee’s Diploma in Sports Nutrition. He is currently working towards a PhD at Liverpool John Moores University.

What’s in this article …

  • What is protein?
  • Where does protein come from?
  • Types of protein
  • Benefits of protein
  • Does protein give you energy?
  • How much protein do I need?
  • The best time to eat protein
  • The downside of a high-protein diet

What is protein?

Protein is often described as one of the ‘building blocks of life’. While it’s not a particularly original or ground-breaking description, we’re sticking with it because it hits the nail on the head. As humans, we’re a walking, talking culmination of more than 10,000 tiny proteins that are responsible for repairing our muscles, building strength, growing hair and nails, and carrying oxygen around our body in our bloodstream.

To find out more about this fundamental fuel, we’re answering all the big protein questions with help from sports nutritionist James Hudson.

At a glance

  • Protein is responsible for many essential functions in your body including muscle repair
  • It’s made up of amino acids – some made by our bodies, others that have to be eaten
  • There are two types of protein you can eat – animal and plant
  • Protein is a great source of slow-release energy

The science of protein

Protein is one of the pillars of a healthy, balanced diet - and essential for our bodies to work properly. Officially, it’s known as a macronutrient, which means we need to eat large amounts.

Zoom in on protein and you’ll see it’s made up of a chain of amino acids. Each different amino acid powers a different function inside our bodies - ranging from tissue repair to chemical reactions.

“Your body responds to any protein consume by absorbing it, before breaking it down into these hugely useful and important amino acids,” says sports nutritionist James Hudson.

From there, these amino acids go off to do their specific job, helping you to stay fit and healthy.

Need to know: Protein is a macronutrient that’s made up of amino acids and is absolutely crucial for humans to develop and survive.


Where does protein come from?

As humans, we get our protein from two main sources:

  • Natural protein your body produces
  • Protein from foods you eat

Making sure you top up your protein levels – especially around times of high activity – is important. But it’s not the full story. The balance of protein types is also as important as the amount – and that’s to do with those amino acids again.

There are 21 amino acids that humans need to survive and be healthy. These are divided into groups of nutritionally essential and non-essential.

Essential amino acids

There are nine amino acids all humans need but which you can’t produce yourself. That’s where the ‘essential’ factor comes in - because you have to get them from protein in your diet.¹

The essential amino acids² are:

  1. Lysine
  2. Histidine
  3. Threonine
  4. Methionine
  5. Valine
  6. Isoleucine
  7. Leucine
  8. Phenylalanine
  9. Tryptophan


Non-essential amino acids

The remaining 12 amino acids can be made by your body, which means you don’t need to get them from protein in your diet. These non-essential amino acids are created by your body using essential amino acids or existing protein cells.³

They are called:

  1. Arginine
  2. Cysteine
  3. Asparagine
  4. Glutamate
  5. Serine
  6. Taurine
  7. Alanine
  8. Glutamine
  9. Aspartate
  10. Tyrosine
  11. Glycine
  12. Proline

Need to know: There are two sources of protein – eating provides essential amino acids and your body makes non-essential amino acids. You need a balance of all these to be healthy.

Types of nutritional protein

Once you get into protein that comes from food, you’re looking at two main sources - animal and plant. Both have their benefits, and both can be enjoyed as part of a healthy, balanced diet.

Animal protein

Sources: Eggs, meat and milk

Benefits: Animal proteins are also known as ‘complete protein’, as they include all the essential amino acids you need in your diet. These protein-rich foods are great for building muscle mass and repairing your tissues after a workout.

Drawback: Some animal proteins – particularly red meat - may be high in cholesterol and fat. If you’re trying to fuel your strength and gym sessions, eating a mix of poultry and fish, as well as protein-rich red meat, can help keep fat levels down.

Here are some of the best sources of animal protein, per 100g:

  • Chicken breast (grilled, no skin): 32g
  • Chicken thigh (casseroled, no skin): 25.6g
  • Salmon (grilled): 24.6g
  • Turkey breast (grilled, no skin): 35g
  • Boiled Eggs: 13g

Plant protein

Sources: Tofu, beans, peas, nuts

Benefit: Many protein-rich plant sources - particularly beans and lentils - are lower in fat when compared to animal proteins. This helps to minimise the associated health problems of a high-fat diet.

Drawback: Not all the essential amino acids we need can be found in all plant proteins. If you’re a vegan, you might want to consider how supplements could help you get the right balance. Quinoa is a good source of plant-based complete protein.

Here are some of the best sources of plant protein, per 100g :

  • Peanut butter: 22.8g
  • Tofu (steamed): 8.1g
  • Chickpeas (canned): 8.4g
  • Peas (Frozen and reheated): 5.7g
  • Baked beans: 5g
  • Quinoa: 13.8g

Need to know: There are two types of nutritional protein – animal protein and plant protein. Each have benefits and drawbacks and are best enjoyed in balance.

Benefits of protein

We’ve already touched on the huge importance of protein for our health. Now we’re diving into the details of the power of protein. These macronutrients can:

  • Repair muscles – “In the body, repairing muscles is its main role of protein,” says James. “We use protein to grow and repair bone and muscle tissue.”
  • Send signals – some proteins help to communicate signals between cells in your body, causing them to react or activate in some way
  • Cause chemical reactions – proteins act as catalysts to many crucial reactions in your body, such as your metabolism and DNA replication
  • Create structural tissues – parts of your anatomy, like hair and nails, grow and are maintained thanks to proteins in your body

Need to know: Protein has many proven benefits for humans, including muscle repair, signal-transmitting, aiding chemical reactions and creating structural tissues.

Does protein give you energy?

Yes, protein is one of the big three suppliers of energy:

  • Carbohydrates
  • Fats
  • Proteins


Type of energy

Amount of energy in 1g (kcal)¹⁰








One of the major benefits of protein of an energy source is it’s a slow-release energy. The complex chain of amino acids takes longer for the body to break down than fats and carbohydrates, giving you steady stream of energy over time.

That’s why protein is so important when you’re pushing yourself. With protein-rich fuel in the tank, you could smash your PB on the treadmill, push yourself further in your workout class or get those endorphins flowing during intense exercise.

Need to know: Protein, carbs and fats are your three main sources of energy – but protein is the one that gives you slow-release, long-lasting energy.

How much protein do I need?

The average adult needs to eat around 50g of protein every day, says the NHS. ¹¹ But there are several factors impacting how much you need, including:

  • Height
  • Weight
  • Metabolism
  • Exercise level

This means you should use this as a rule of thumb guide. For a personalised figure, your weight is the best place to start. A healthy amount of protein is 0.75g of protein per kilogram of bodyweight¹².

But this changes if you’re trying to build muscle mass. When you’re hitting the gym and burning lots of energy, you need protein to keep you going throughout your workout – but also afterwards to aid muscle repair and recovery.¹³

Need to know: You can work out how much protein you should be eating based on your weight – but you should also take into account your physical activity levels and metabolism.

The downside of a high-protein diet

While it’s not dangerous to eat too much protein, having too many meals that are protein-rich could mean you miss out on other macros.

“You can’t have too much protein in your body,” says James. “It’s a bit of a myth that eating a high amount is dangerous to your health – but you can have too much in your diet that you neglect other foods.”

Reassess your diet and make sure you’re getting all the nutrients you need from other food groups – like fruits, vegetables and even some fats.

Need to know: Eating too much protein could cause some unpleasant symptoms but can easily be soothed by rebalancing your diet.

In summary:

Protein is an essential part of our diet, fuelling a huge range of human functions. How much you should be eating depends on your natural build, as well as your fitness goals. Settle into a protein-rich diet that’s in line with your workout schedule, and you’ll start to see the rewards very soon - with a whole lot of sweat and determination along the way.















Headshot of James Hudson

Performance Nutritionist at Nutrition in Sport

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