Dietary Protein

Dietary

Protein

Introduction

Dietary protein is an essential macronutrient which helps the growth of new tissue and the remodeling of skeletal muscle after exercise. Proteins have many different roles in the human body. For athletic performance, protein is commonly associated with muscle and movement.

However protein has many other important roles including hormone production, providing structure for cells and tissues, supporting immune system function, moving essential molecules around the body, and enzyme production. Therefore, consuming sufficient protein in the diet is important for all athletes.

The information in this section will discuss the role of protein in the body, how protein supports recovery, and practical advice on how to incorporate protein into an athlete’s diet.

The process of building muscle

Exercise increases both MPS and MPB, therefore muscle protein turnover is high. The exercise-associated adaptations that occur within muscles will depend on the type of exercise performed, as well as the dietary nutrients available.

Net protein balance

It is important to ensure that athletes are in either a positive net protein balance, or muscle maintenance, to ensure that they are not losing muscle mass (see below). Athletes can achieve this by regularly consuming adequate amounts of protein in meals and snacks, alongside completing resistance exercise.

Amino acids

Proteins are composed of units called amino acids. There are 20 different types of amino acids, and it is the sequence of these amino acids (also known as a polypeptide chain) that determines the structure and function of a protein.

Amino acids are classified into two groups: essential and non-essential. The body can synthesize (produce) non-essential amino acids, but essential amino acids (EAAs) must be consumed through the diet. Foods which contain all EAAs are considered ‘complete’ dietary proteins. This is typically animal-based foods such as meat, poultry, fish, eggs, and dairy foods. Plant-based foods (fruits, vegetables, grains, nuts, and seeds) often lack one or more EAA. Combining different plant-based foods that are high in protein is a good strategy for achieving intake of all EAAs within a meal.

Examples of complete dietary proteins

Essential amino acids

Not produced by the body
Important to consume within diet
Histidine, isoleucine, leucine, lysine,
methionine, phenylalanine, threonine,
tryptophan, valine

Non-essential amino acids

Produced by the body
Not crucial to consume within diet
Alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine

Dietary protein source and quality

Protein sources contain different amino acid profiles. Both animal-based and plant-based protein sources can play important roles in a balanced diet by contributing a range of amino acids. Creating meals with a mixture of various protein sources, whether from animal- or plant-based sources, helps ensure nutritional needs are met.

Protein quality refers to the nutritional value and bioavailability of the protein. It assesses the ability of a protein to provide EAAs in proportions that meet the body’s requirements for growth, maintenance, and repair. Protein quality is measured using a variety of indices, however the most accepted and understood indexes are the Protein Digestibility Corrected Amino Acid Score (PDCAAS) and the Digestible Indispensable Amino Acid Score (DIAAS). Food sources with high PDCAAS values include eggs, ground beef, whey, casein, milk, and soy.

Common sources
of dietary protein

1 medium
chicken breast

Serving size: 4.2 oz / 120 g

Protein: 38 g

1 small sirloin steak

Serving size: 3.9 oz / 110 g

Protein: 37 g

Small portion lean ground beef

Serving size: 3.5 oz / 100 g

Protein: 22 g

Half a can of tuna

Serving size: 3.2 oz / 90 g

Protein: 21 g

1 salmon fillet

Serving size: 3.5 oz / 100 g

Protein: 23 g

1 cod fillet

Serving size: 3.6 oz / 100 g

Protein: 24 g

Prawns

Serving size: 4.2 oz / 120 g

Protein: 21 g

3 medium eggs

Serving size: 6.4 oz / 180 g

Protein: 21 g

1 cup of
cottage cheese

Serving size: 8.8 oz / 250 g

Protein: 23 g

Greek yogurt

Serving size: 7.1 oz / 200 g

Protein: 20 g

1 large glass
of milk

Serving size:
20.1 fl oz / 568 ml

Protein: 19 g

Skimmed milk powder

Serving size: 2.1 oz / 60 g

Protein: 21 g

1 scoop of whey, soy or casein protein

Serving size: 1.1 oz / 30 g

Protein: 20-25 g

Tempeh

Serving size: 3.5 oz / 100 g

Protein: 21 g

Seitan

Serving size: 3.5 oz / 100 g

Protein: 24 g

Soy flakes

Serving size: 1.8 oz / 50 g

Protein: 27 g

Quinoa

Serving size:
10.6 oz / 300 g

Protein: 21 g

Mixed nuts

Serving size: 3.2 oz / 90 g

Protein: 20 g

Tofu

Serving size: 3.5 oz / 100 g

Protein: 24 g

4 tablespoons
peanut butter

Serving size: 2.1 oz / 60 g

Protein: 19 g

Mycoprotein

Serving size: 7.1 oz / 200 g

Protein: 22 g

Lentils

Serving size: 8.8 oz / 250 g

Protein: 19 g

Chickpeas

Serving size: 8.1 oz / 230 g

Protein: 17 g

1 cup of edamame

Serving size: 7.1 oz / 160 g

Protein: 18 g

Baked beans

Serving size: 14.7 oz / 415 g

Protein: 21 g

Daily protein intake recommendations

Female athletes require protein to support adaptation and muscular repair in response to exercise. It is recommended that athletes consume 1.2 – 2.0 grams of protein per kg of body mass per day (g/kg BM/day).

Athletes might require higher protein intakes to:

• Optimize muscle adaptation/recovery during periods of higher
frequency/intensity training, or a new training stimulus

• Help maintain muscle mass if sudden or reduced inactivity occurs (e.g., following an injury)

• Prevent increased protein oxidation if carbohydrate intake is low,
or if an athlete has low energy availability

Timing of protein intake throughout the day

To maximise exercise-associate muscle adaptations, athletes are advised to evenly distribute their consumption of protein during meals and snacks throughout the day, in combination with appropriate quantities of other macro- and micronutrients. Consuming a meal or snack which includes ~20-40g protein every 3-4 hours is advisable.

Plant-based proteins

Athletes may choose to follow a plant-based diet. The anabolic properties of plant-based proteins are generally lower, likely due to their reduced EAA content when compared to high-quality animal-derived proteins, with many plant-derived proteins being deficient in one or more amino acid(s).

Despite this, with careful planning, athletes following a plant-based diet can consume adequate protein from plant-based foods. Those relying on plant-based proteins should ensure they are eating a variety of foods in order to meet their EAA needs, and to support recovery and training adaptations. Combining different plant-based protein sources throughout the day in meals and snacks is a good strategy to ensure that all EAAs are consumed. It should be noted that there are several plant-based foods which are considered complete proteins, and therefore are not lacking in any EAAs (see below).

Tofu

Edamame

Tempeh

Quinoa

Buckwheat

Considerations

Plant-based protein, in its natural form, has lower natural digestibility compared to animal-based protein. Processing methods such as heating, soaking, or boiling can improve the digestibility of plant-based proteins. By combining different food groups, increasing portion sizes, and enhancing amino acid availability through processing or cooking, athletes following a plant-based diet can effectively stimulate MPS throughout the day.

Regarding the use of plant-based proteins for recovery and muscle gain, several studies have shown that consuming 30g of protein from plant-based sources (potato or a blend) leads to similar increases in MPS compared to milk protein. Therefore, plant-based proteins are a suitable option post-exercise.

Protein intake around exercise

Before and during exercise

Exercise causes a slight increase in the oxidation of protein, however protein is not an important energy source during exercise. The energy requirements for exercise are primarily met by carbohydrate and fat. Therefore, protein intake is not a priority immediately prior to, or during exercise.

Post-exercise (see for additional information)

While there does not appear to be a defined ‘window of opportunity’, it is important for athletes to incorporate high quality protein into their diet. Consuming protein source(s) which are rich in leucine and contain all EAAs is generally regarded as an effective means to ‘turn on’ and support maximal rates of MPS immediately after exercise. Ideally, meals/snacks should include ~20-40g of protein, or 0.25-0.30 g/kg BM of protein. When participating in intense whole-body exercise, the protein serving post-exercise may be increased up to 30-40 g.

Post-exercise, optimal choices include a balanced meal containing both lean protein and carbohydrates, or any of the snack choices below:

The importance of leucine

Foods with a high leucine content include:

Chicken

Turkey

Pork

Tuna

Salmon

Pine nuts

Protein powders

Protein powders provide a convenient way for athletes to consume additional protein within their diet. Ideally, the majority of an athlete’s protein intake should be consumed via whole foods. However, protein powders may be useful when an athlete struggles to meet their daily protein needs through whole foods, or when access to high quality protein is limited e.g., when travelling.

Whey and casein protein (both milk proteins), as well as soy protein, are complete protein sources which have been shown to promote MPS. Soy protein provides a suitable option for athletes following a vegan diet, as well as protein blends which contain a range of plant-based proteins to achieve a full complement of EAA.

Whey protein isolate

25-30g serving size suggestion

~2.5g Leucine per serving

Soy protein isolate

25-30g serving size suggestion

~2.0g Leucine per serving

Casein protein

25-30g serving size suggestion

~2.0g Leucine per serving

Protein and sleep

Sleep is often an overlooked occasion for recovery. If protein is ingested prior to sleep, it is digested and absorbed, and used in muscle remodeling. Some pre-sleep protein options include:

Hot cocoa (made with milk and/or chocolate protein powder)

Bowl of Greek yogurt

Cottage cheese on crackers

Protein shake

Female specific requirements

Research investigating protein requirements specifically for female athletes is limited. However, determining optimal intake within total energy needs is crucial. Female athletes should aim for 0.25-0.30 grams of protein per kilogram of body mass (per serving) to meet their individual needs. Additionally, they should prioritize nutrient-dense protein sources and consider the timing of intake, especially after exercise.

Menstrual cycle

A small number of studies have suggested that there is a small increase in protein utilization at rest and during exercise during the luteal phase of the menstrual cycle (see for more information).