Protein 101


What is protein + Why do we need it?

Protein is essential for the maintenance, growth and repair of all cells in the body. They are also involved in a large variety of metabolic interactions in cells. In an average UK diet you will get 16% of your daily dietary energy from the protein. 1g of protein are equivalent to 4kcal. After water protein in the most common compound in the body, 43% of all proteins will be associated with muscle, 16% in your blood and a further 15% is found in your skin.


What is the structure of proteins?

Protein is essentially large molecule that is made up of long chains of amino acids. Amino acids are the building block of proteins. There are 20 different types of amino acids, with 8 essential amino acids that adults need in our diet. They are called:

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

There is a further 7 amino acids that are considered essential in children. The other non-essential amino acids do not have to be provided through our diet.

Thanks to the fitness supplements industry most people have heard of whey protein, which is a mixture of proteins that are found in the by-product liquid found when making cheese. Whey proteins, casein and proteins found in egg whites and soy casein are considered to provide the essential amino acids to create muscle growth as well as the correct nitrogen balance. (Campbell et al 2007)

Are protein supplements necessary in order to put on muscle to increase your protein intake? No they are not, but can they be a quick and convenient way of getting the essential proteins in after a work out.

Top of the essential amino acids list leucine is said to be the limiting factor in initiating muscle growth and it the most important amino acid needed after a hard work out.


How much protein do you need?

The current recommended dietary allowance for protein for both men and women in the uk is 0.75g per kg of body weight. As you can see below the amount of protein you need will depend on your age, with it reaching a peak between 15-50 yrs. The amount of protein you require can also be affected if you are growing, pregnant, breast-feeding or an athlete/looking to put on muscle. According Fink et al (2009) the amount of protein for endurance athletes is 1.2 to 1.4g while strength or power athletes should have 1.2-1.7g per kg of body weight. Other researchers have suggested up to 2g per kg to prevent muscle loss in athletes. Phillip & Van Loon (2011)

  • 1-3yrs = 15g
  • 4-6yrs=20g
  • 7-10=28g
  • 11-14yrs = 42g
  • 15-50yrs – men = 56g
  • 15-50yrs – women = 45g
  • 50+ = 53g

However despite adults only needing around 42-53g of protein, our average intake in the uk is 88g for men and 64g for women which is pretty staggering. Generally speaking it is very unlikely you are not getting enough protein in your diet obviously this is dependant on lifestyle choices.


Where can you get protein?

Different foods will be made up of different amino acids. You can get protein from many different sources but the most obvious and most popular in the UK with 37% is from meat. However it may surprise you to know the next most prominent source of protein is cereals/grains at 23%. Sources of protein can be found in the form of meat, fish, dairy, pulses, nuts and cereals. Animal protein will generally have a higher biological value than plant sources as their structure and variety of amino acids will be more similar to human protein cells.

Plant based proteins:

You can easily get enough protein through plant-based sources, the recommendation in most diets is a selection of two different sources. This is called or complementary action of protein to enable you to get the variety of essential amino acids that you need. For example this can be achieved through mixing rice and lentils or bread and beans.

Animal proteins:

Animal protein will contain a fuller range of all the essential proteins that you need in your diet. However it is recommended to watch the fat levels in some higher protein foods, as they tend to be higher in saturated fats.

Harvard’s University did a study over 16 years, which investigated the long-term weight changes found in protein consumption and high GL foods (higher glycemic load). The analysis found Fish, nuts, and yogurt proteins were linked to less weight gain, and red meat proteins to more.  Smith et al (2015)

Food Protein (g)
Chicken breast grilled N/A skin, 100g 32
Steak, 100g 31
Pork chops (boneless)– 100g 31.6
Lamb lean grilled – 100g 29g
Tuna 85g 25
Octopus – 85g 25g
Tinned Anchovies – 85g 24g
Salmon fillet, 100g 24
Cod, 100g 20
Soya bean, 50g dry weight 18
Lean mince-95% Beef 85g 18g
Peeled prawns, 75g 17
Half-fat cheddar, 50g 16
Eggs (2 medium) 14.2
Cottage cheese, 100g 14
Peanuts 50g 13
Black-eye beans, 50g dry weight 11
Lentils, 50g dry weight 12
Red kidney beans, 50g dry weight 11
Edamame 100g 11
Almonds 50g 10.5g
Non-Fat Greek Yogurt 10
Cashews, 50g 8.9
Baked potato, 223g cooked weight 8.7
Tofu, 100g 8
Walnuts – 50g 7.5
Wholemeal pasta,, 50g dry weight 6.7
White pasta, 50g dry weight 6
Soya milk, 200ml 6
Skimmed milk, 200ml 6.6
Seeds – such as pumpkin/squash 25g 6
Wholemeal bread, (2 average slices) 5.5
Quinoa – 100g cooked 4
Vegetables, 1/2 cup 2
Fruits e.g. apple, banana, orange 1

When to eat protein?

Your body can only deal with 20-25g of protein every two to three hours any more than that and your body will just secrete or find a way to get rid of the rest. Therefore each meal matters when it comes to protein and the best way is to have it little an often. There is no point in having massive after a workout cause you just wont absorb it all. It is best to have around 20g of protein per meal to keep your overall daily protein intake high. However most people on average unless you have a cooked breakfast everyday ,will have very little protein in the morning and rely more on lunch and mainly dinner for their protein intake. If you have little protein in your lunch and breakfast it will have no benefit to maintaining good muscle health. A study by Mamaerow et al (2014) found that muscle protein syntheses was 25% higher when protein amounts where evenly distributed across breakfast, lunch and dinner compared to relying on it just at dinnertime. The university of Illinois also found that adults need at least 30g of protein in two or more meals to maintain healthy muscles.

As a result of intense physical activity your muscles will start to break down which is why it is essential that athletes get enough protein in to maintain their muscle health and promote growth and repair. It is recommend eating protein within 30 minutes of an intense workout as this is when the muscles are most sensitive to protein absorption. Phillips (2012) For more information look at my blog post on post workout nutrition, its even got a handy recipe for a post workout snack.

There have also been studies that have proven that protein consumption in the last 2 hours before you go to sleep may cause increase muscle growth and strength. Most of the changes reported were to fast twitch muscles fibres suggesting this would be more useful for power or speed athletes than endurance.

High protein diets for Weight loss:

As protein rich food tends to keep you feeling fuller for longer it is not surprising that a lot of weight loss diets will be higher in protein. These diets often contain lean meats or low fat options especially with regards to diary products. In the short term is said that high protein, low carb diets tend to get you to loose weight quicker than low fat diets. However the research doesn’t show much of a difference in the long term.

There is a lot of controversy about having high protein diet and there is growing evidence to show that it’s not that good for you especially for kidney function. When you have high amounts of protein it can affect your nitrogen balance and increase the urea or pee that we make which can increase the filtration rate in the kidney causing it to work harder. It is also important to take into consideration the amount of calcium you are taking in with regards to protein, as this can be essential to bone health. Bonjour (2011) If you have a low calcium intake then a high protein diet could actually be detrimental to your bone health. You can read more about the effects of calcium on bone health in my other blog post about Osteoporosis. High protein diets can also affect your liver function again due to the body’s ability to get rid of the extra nitrogen that will be circulating round your body. Bilsborough & Mann (2006)


Phillips SM, Van Loon LJ. Dietary protein for athletes: from requirements to optimum adaptation. Journal Sports Science 2011;29(Suppl 1):S29-38.

Fink HH, Burgoon LA, Mikesky AE. Endurance and Ultra-Endurance Athletes: Practical Applications in Sports Nutrition. Sudbury, MA: Jones and Bartlett; 2009.

Campbell B, Kreider RB, Ziegenfuss T, La Bounty, P, Roberts, M., Burke, D., Landis, J., Lopez, H., Antonio, J. (2007) International Society of Sports Nutrition position stand: protein and exercise. Journal International Society Sports Nutrition;4:8.

Layman DK. (2013) Protein nutrition, meal timing, and muscle health. In: Berdanier CD, Dwyer JT, Heber D, eds. Handbook of Nutrition and Food. 3rd ed. Boca Raton, FL: CRC Press; 2013:861-867.

Phillips SM.(2012) Dietary protein requirements and adaptive advantages in athletes. British Journal of  Nutrition 108(Suppl 2):S158-167

Bilsborough S, Mann N.(2006) A review of issues of dietary protein intake in humans. International Journal Sport Nutrition Exercise Metabolism. 16(2):129-152.

Mamerow MM, Mettler JA, English KL, Casperson, S.L., Arentson-Lantz, E., Sheffield-Moore, M., Layman, D.K, Paddon-Jones, D. (2014) Dietary protein distribution positively influences 24-h muscle protein synthesis in healthy adults  Journal of Nutrition doi: 10.3945/jn.113.185280.

Bonjour JP. Protein intake and bone health.(2011) International Journal Vitamin Nutrition Research 81(2-3):134-142.

British Nutrition Foundation: Protein (2015)

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