What does protein do?

What does protein do?

 By Alister Gardner  

In 2009, less than a year after my inauguration into running (the beast that was X-Trail Sutton) I switched to a vegetarian diet and by 2012 I had completely cut out all animal products from my diet. I did it instinctively knowing that a lack of protein was not going to be a problem, however, it was a question I was asked often and got me thinking about how nutrition plays a role in our lives (especially as an athlete) and in turn led me to do a diploma in nutrition.

Fast forward a few years, and while we see ‘plant-based’ protein in all forms these days (from powder proteins to chick’n cutlets) there still doesn’t seem to be a greater depth of understanding as to what exactly protein is and how much we really need (especially in the sports world). So in this article we’re going to take a closer look at this particular macronutrient because it does a lot more than just build muscle:

What is a protein?

A protein is a combination of amino acids, just as words are a combination of letters. There are twenty amino acids, nine of which are essential as the body cannot synthesise them itself, and eleven non-essential amino acids, meaning the body can make them itself. Six of these, however, are conditionally indispensable, meaning that under certain circumstances, as with a critical illness, the body cannot make them. As with words, there is an almost infinite combination of proteins, each with its own purpose, that can be made by these amino acids.

Protein sources that include all of the essential amino acids are called complete or high-quality proteins: these typically come from animal sources or a select few plant sources such as quinoa, soy and hemp. Most plant-based proteins sources are incomplete. However, we don’t need to consume all of the essential amino acids in one meal (1); of the 300 grams or so of protein synthesised by the body every day, over 200 grams are recycled — this reserve is known as our amino acid pool and is in constant turnover. Furthermore, a diverse plant-based diet can provide all the amino acids that are required (2). Many meals, such as hummus and pita or beans and rice, will already provide the range of amino acids necessary

What does protein do?

Because our muscles are made up of proteins, it is easy to connect protein consumption with muscle recovery and growth. Proteins are also responsible for all tissue growth, including tendons, hair, nails and skin. Furthermore, proteins are also:

  • Required to form hormones, enzymes and neurotransmitters, all essential for numerous metabolic functions in the body. For example, they are important for the storage and use of carbohydrates, including restocking glycogen (a key energy source) after a workout.
  • Used for creating antibodies as part of our immune system.
  • Necessary for the formation of hemoglobin, which transports oxygen in the blood (check out our iron blog for more info).
  • A fuel source (however they are far from an ideal source as they contribute between only 2 and 5 % (3) and are better used for other functions in the body.
  • Crucial for controlling body fluid volumes and hydration.

How much protein do we need?

The Academy of Nutrition and Dietetics recommends that the average individual should consume 0.8 grams of protein per kilogram, based on the recommendation that the average person performs 30 minutes of physical activity per day.

For elite athletes in high resistance sports such as boxing and football, this figure can rise to 2.5 to 3 grams per kilogram at specific periods in the season; for instance, a college football player who is aiming to gain muscle mass and reduce body fat in pre-season training (4, 5), is following a short term (4-6 weeks) diet requirement, and such a diet is not recommended over the long term. However, for a typical resistance athlete looking to maintain muscle mass and rapidly recover from in-season training sessions and competitions, the ratio is between 1.4 to 1.8 grams of protein per kilogram of body weight (5).

Similarly, for moderate intensity endurance athletes seeking to prevent significant loss of muscle mass due to their high volume of training, and in order to optimise recovery between workouts, 1.2 to 1.4 grams of protein is required per kg of body weight (6,7). Elite endurance athletes would require closer to 1.6 grams per kilogram. Recreational endurance athletes require around 1 gram per kilogram of body weight (8).


Female athlete needs

For female athletes, these requirements are 10-20% lower as they burn a lower percentage of protein as fuel: usually around 2% as opposed to 5% by men (3). This is because estrogen has been shown to have a protein-sparing effect by reducing the reliance on amino acids as fuel and increasing fat utilisation.

In real life terms that equals: 


Body weight in lbs (equivalent in kgs)

%DV protein  (grams)

Endurance athlete daily

 protein requirements 

(1.2-1.4 g/kg body weight)

Resistance athlete protein requirements

(1.4-1.8 g/kg)





130 (59)






160 (72.3)






190 (86.4)







A wide variety of research has shown that on average men easily exceed these needs with an average of 1.8 grams per kilogram, and women are closer in line at 1.3 grams per kilogram.

If about 5% of energy used by a 160 lb male runner during a 1h30 (approximately 1200 k Cal) run is protein, then at 4 calories per gram, this is 15 grams of protein used to fuel his run. This energy makes up a large part of that difference in protein requirements needed by an endurance athlete. However, this is a little simplistic as it is measuring caloric energy needs for the activity only, and not the muscle synthesis since glycogen replenishment and metabolic recovery take place afterwards, but it does remind us that protein is still used as an energy source and needs to be replaced.

No harm in too much?

If excess protein means excess calories it will be stored as fat, not as muscle. We cannot pump protein supplements in the hope of building muscle and improving performance; only regular training with the right mix of nutrients can do that.

Excessive protein consumption means excess nitrogen that must be excreted: it is the nitrogen balance that is often used by researchers to determine whether individuals are consuming enough protein. High levels of nitrogen excretion can create a burden on the kidneys and accelerate pre-existing renal disease.

Also, supplements of specific amino acids can interfere with the absorption of other amino acids and, depending on the type of protein source, may also include high levels of fat.

How and when to take protein for maximum recovery?

It is suggested that our protein absorption rates drop at above 30 grams of protein per meal; therefore, spreading our protein intake evenly throughout the day will allow for maximum assimilation. So for breakfast, if we eat a bagel with peanut butter, or oatmeal with a handful of nuts plus a coffee with soy or cow's milk, we are already at 15 grams in a relatively small meal.

For active individuals and athletes training regularly, our energy requirements are already higher and so our protein intake should naturally grow in proportion as well (assuming we are eating a well balanced diet and not just chomping XACT ENERGY fruit bars and pretzels between training sessions). It is easy to find the protein content in the nutritional value table shown on products available in the supermarket. People are often surprised to see protein where they were not expecting it: for example, many whole wheat pasta brands have 10-14 grams of protein per portion.


The famous 30-60 minute recovery window

Following a moderate to intense training session, there is also an important window of recovery within which the body can be helped by proper fuelling (10). In the 30-60 minutes after a training, consuming a 200-300 calorie snack with a carb:protein ratio of 3-4:1, we can significantly help our bodies replenish depleted glycogen reserves (very important for folks training daily or twice a day) and thus optimise muscle synthesis as part of the recovery process.

It is here that a bar like XACT PROTEIN can be useful as they are portable snacks that respond directly to the body’s post training needs.

Also, when travelling, we find ourselves doing our best to avoid junk food and turning to salad options that may be limited in terms of overall energy and protein needs, so again, a protein bar is a handy tool in these situations.

Another situation in the context of day to day life, is the satiating effects of protein and complex carbohydrates (and to some extent fat); often we begin to get hungry late in the afternoon and this can be distracting when we go to train in the evening. A protein bar makes for a better snack than a chocolate bar for example, but it is important to consider those pre-workout carbs to help you sustain your energy levels through the workout too.


1. Protein and vegetarian diets. 2013 Aug 19 Marsh KA, Munn EA, Baines SK.
2. Position of the American Dietetic Association: vegetarian diets. J Am Diet Assoc. 2009
3. Percentage of protein used in 1 hour’s exercise ****
4. Effects of exaggerated amino acid and protein supply in man. Fern EB, Bielinski RN, Schutz Y, Experientia. 1991
5. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr. 2017
6. Macronutrient Intakes in 553 Dutch Elite and Sub-Elite Endurance, Team, and Strength Athletes: Does Intake Differ between Sport Disciplines? 2017 Feb. Floris Wardenaar, Naomi Brinkmans, Ingrid Ceelen, Bo Van Rooij, Marco Mensink, Renger Witkamp, and Jeanne De Vries
7. Nutrition and Supplement Update for the Endurance Athlete: Review and Recommendations. 2019 Kenneth Vitale, and Andrew Getzin
8. Estimated protein requirements for athletes, Clinical Sport Nutrition. Louise Burke and Vicki Deakin.
9. Energy requirements during a one-hour run at 65-75% of VO2 Max, Clinical Sport Nutritional, Louise Burke and Vicki Deakin.
10. Nutrition and Supplement Update for the Endurance Athlete: Review and Recommendations. 2019, Kenneth Vitale and Andrew Getzin