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What is protein and how does it help build muscle?

Rob Hobson
Article written by Rob Hobson

Date published 04 February 2022

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All athletes know the importance of protein for maximising gains from exercise, but how does it work, how much do you need and when should you take supplements? Nutritionist Rob Hobson explains.

What is protein?

All proteins are made up of smaller molecules called amino acids, which link together to form complex structures. There are 20 different amino acids; nine of these cannot be made in the body and so must be obtained from the diet.

Proteins are required to grow, repair, and produce muscle, bone, tendons, skin, enzymes, hormones, and various other components with critical functions in the body.

How much protein do people currently get?

Dietary guidelines recommend a daily intake of 0.75g of protein per kg of bodyweight.

On average, this comes to approximately 56g for men and 45g for women. The National Adult Nutrition Survey 2011 showed that men consume 93g and women 70g – more than enough.

However, some groups, such as pregnant women, those recovering from illness or injury, and athletes engaged in endurance or strength-based sports, do need more protein in their diet.

What foods are high in protein?

When choosing a food rich in protein, it is essential to consider the quality and quantity. Foods such as meat, poultry, fish, dairy, eggs, and whole sources of soy (tofu, edamame beans, tempeh) contain all the essential amino acids that need to come from the diet; these are high-quality proteins, so should feature heavily in an athlete's diet.

Plant-based sources such as beans, pulses, lentils, nuts and seeds contain some, but not all, of the essential amino acids. Athletes following a vegan diet should include a variety of these foods throughout the day. They can also supplement their diet with a vegan protein powder.

"Muscle protein synthesis (MPS) is the natural process where protein is produced to repair the damage to muscles caused by intensive exercise."

How does protein help to build muscle?

After consuming protein, enzymes in the stomach and small intestine break them down into chains of amino acids called peptides. Training causes microtears in muscle, which triggers an immune response involving stem cells and growth hormone, which use the amino acids to repair the damage.

These amino acids are sent to damaged muscle cells to stimulate the growth of myofibrils, which are the filaments that make up muscles. These myofibrils fuse with damaged areas of muscle fibres, and this is the process that helps to make muscles bigger and stronger.

How much protein do athletes need?

Most athletes get more than enough protein, but this is often at the expense of carbohydrates in the diet. This situation may not be beneficial for those engaged in endurance or team sports.

Recommendations for protein intake among athletes are given as grams per kg of body weight per day, and vary depending on the type of sport.

Protein intake recommendations per kg of bodyweight

Regular physical activity
1.0 - 1.2g
Endurance athletes
1.2 - 1.4g
Team sports (rugby, football)
1.2 - 1.4g
Strength/power athletes (weightlifting, wrestling)
1.2 - 2.0g

Timing is crucial, and it is generally considered that consuming protein shortly after exercise is beneficial for muscle protein synthesis (MPS). MPS is the natural process where protein is produced to repair the damage to muscles caused by intensive exercise.

Consuming protein after a session also helps the skeletal muscle respond to training, resulting in more effective muscle conditioning.

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When should I take protein after exercise?

Muscle gains in response to resistance exercise are influenced by the training load and the amount, type, and timing of protein intake during the following 24-48 hours.

The anabolic muscle response (growth and building) peaks after consuming 20-25g of protein. More than this doesn't appear to have a significant effect. This means that consuming around 25g of protein post-training and at regular intervals (every few hours) across the day is a more beneficial strategy than higher, less frequent doses.

What type of protein should I take?

The amino acid leucine increases the rate of protein synthesis. A post-training meal should be in the form of a rapidly digested protein with a high leucine content, such as whey, skimmed milk, and eggs.

Whey protein seems to be the most effective at increasing MPS due to its rapid digestion and absorption, as well as its composition of amino acids. Other proteins consumed over the day should be lean and high-quality, containing all the essential amino acids, and predominantly from animal sources, supplemented with soy, beans, cheese, and nuts.

Athletes on a plant-based diet should consider a vegan protein supplement.

Protein before bed

Hot drink in white mug on table

As we sleep, our muscles repair themselves and grow – the body produces more growth hormone when we're asleep. Taking protein before bed, such as in a hot drink, means your muscles can take advantage of this increase in growth hormone.

Do you need a protein shake?

You can get all the protein you need from your diet, but sometimes a protein shake may be more convenient. These shakes are most useful after a training session, as they take very little preparation and can be consumed on the go.

Shakes also guarantee the correct quantity and quality of protein, comprising all the essential amino acids, including leucine. Athletes with a high requirement for protein or those following a vegan diet may choose to consume more than one protein shake a day to ensure sufficient intake.

Is too much protein bad for you?

There is no benefit to consuming more protein than is required. It has been claimed that consuming more than 3g per kg of bodyweight a day has adverse side effects, including kidney damage, increased blood lipoproteins (substances made of protein and fat that carry cholesterol around the body), and dehydration.

Consuming up to 2g per kg of bodyweight a day is not harmful. Still, when trying to keep energy intake constant, this level of protein intake may come at the expense of carbohydrate and fat – a crucial consideration for endurance athletes.

Athletes consuming a high amount of protein in their diet also need to ensure an adequate intake of fluids to avoid dehydration.

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Rob Hobson

About Rob Hobson

Rob Hobson MSc RNutr is an award-winning registered nutritionist (AFN) and sports nutritionist (SENR) with over 15 years of experience. He founded London-based consultancy RH Nutrition, and has degrees in nutrition, public health nutrition and sports nutrition.