What is protein?

Protein is one of the three macronutrients alongside carbohydrates and fats. These are required in larger amounts for the body to function properly and they provide a source of energy. While protein can provide energy its main function is for the growth and repair of muscle, bone, skin, enzymes, hormones and other components critical to bodily functions.

Proteins are made up of smaller molecules called amino acids. There are 20 different amino acids which link together in different combinations to form complex structures. Nine of these amino acids can’t be made in the body and must be gleaned from the diet which is why they are referred to as being ‘essential’.

How much protein does a healthy adult need?

UK dietary guidelines (based on a sedentary population) recommend 56g of protein for men and 45g for women daily. These guidelines are based on a dietary intake of 0.75g protein per kg of body weight¹.

How much protein do we get in our diet?

The National Diet and Nutrition Survey (2020) has shown that protein intake in healthy adults is well above the recommendations as men consume 85g and women 68g daily². Some people may need more protein in their diets, such as pregnant women, those recovering from illness or injury, and athletes engaged in endurance or strength-based sports.

What are the best sources of protein in the diet?

The topic of protein in the diet is just as much about quality as it is quantity. The quality of a protein is gauged on its essential amino acid content and you could also factor in how it appears in a food; for example, a lean steak would be considered healthier that a meat pie or sausage.

Foods such as meat, poultry, fish, dairy, eggs, and whole sources of soy (tofu, edamame beans, tempeh) contain all nine essential amino acids.

Plant-based sources such as beans, pulses, lentils, nuts, and seeds contain some but not all the essential amino acids. People following a plant-based diet should endeavour to consume a variety of different foods rich in protein across the day.

How does an athletes protein requirement differ?

Despite the importance of nutrition many athletes still seem to be confused about what to eat. Commonly, athletes consume above and beyond the amount of protein required to support their needs. This high intake of protein comes at the expense of carbohydrates which in the case of endurance athletes or team sports players may hamper performance.

Understanding protein requirements in athletes is often about establishing a better macronutrient split in favour of carbs rather than dealing with insufficiency.

Recommendations for protein intake amongst athletes vary depending on the type of sport. They are given as grams per kg of body weight per day^3,4.

• Regular physical activity                                                1.0-1.2 g
• 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 key for muscle protein synthesis

Timing is crucial and consuming protein shortly after exercise is beneficial for muscle protein synthesis (MPS). Consuming protein after training is also facilitates the skeletal muscle adaptive response to each session resulting in more effective muscle reconditioning.

Muscle protein gains in response to resistance exercise are influenced by the training load and the amount, type, and timing of protein during the following 24-48 hours. The anabolic muscle response (growth and building) peaks after consuming 20-25g of protein. Excess of this doesn’t appear to have any more significant effect. This means consuming around 25g of protein post-training and at regular intervals (every few hours) across the day is a more beneficial strategy than higher doses less often.

The type of protein is also important

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 and its composition of amino acids. Other proteins consumed over the day should be lean and high-quality, containing all the essential amino acids, predominantly animal sources. These can also be supplemented with soy, beans, cheese, and nuts.

Consuming 40g of casein protein before bed has been shown to increase overnight MPS and metabolic rate as it is broken down and releases its amino acids more slowly⁵.

What is the role of protein in building muscle?

After consuming protein, enzymes in the stomach and small intestine break them down into chains of amino acids called peptides. Training causes microtears which trigger an immune response involving stem cells and growth hormone that use the amino acids to repair the damage. These amino acids are sent to damaged muscle cells to stimulate myofibrils’ growth, which are the filaments that make up muscles. These myofibrils fuse with damaged areas of muscle fibres which is a process that helps to make them bigger and stronger.

Do athletes need protein shakes?

You can get all the protein you need from the diet, but sometimes it may be more convenient to consume a protein shake. 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 of these shakes a day to ensure their intake. Shakes containing less that 20g of protein are better taken alongside a source of carbohydrate as the release of insulin can help with its uptake. You can do this by blending honey and fruit such as bananas or berries.

Is there a danger of consuming too much protein?

There is no benefit to consuming more protein than is required. It has been claimed that consuming more than 3g/kg/day of protein 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/kg/day is not harmful. Still, this level of protein intake may come at the expense of carbohydrate and fat when trying to keep energy intake constant which is a crucial consideration for endurance athletes. Athletes consuming a high amount of protein in their diet need to ensure an adequate intake of fluids to avoid dehydration.

References

1. Dietary reference values for food energy and nutrients for the United Kingdom. Report of the Panel on Dietary Reference Values of the Committee on Medical Aspects of Food Policy. (1991). Reports on health and social subjects, 41, 1–210.
2. https://www.gov.uk/government/statistics/ndns-results-from-years-9-to-11-2016-to-2017-and-2018-to-2019
3. Phillips, S. M., & Van Loon, L. J. (2011). Dietary protein for athletes: from requirements to optimum adaptation. Journal of sports sciences, 29 Suppl 1, S29–S38.
4. American Dietetic Association, Dietitians of Canada, American College of Sports Medicine, Rodriguez, N. R., Di Marco, N. M., & Langley, S. (2009). American College of Sports Medicine position stand. Nutrition and athletic performance. Medicine and science in sports and exercise, 41(3), 709–731.
5. Res, P. T., Groen, B., Pennings, B., Beelen, M., Wallis, G. A., Gijsen, A. P., Senden, J. M., & VAN Loon, L. J. (2012). Protein ingestion before sleep improves postexercise overnight recovery. Medicine and science in sports and exercise, 44(8), 1560–1569.

Useful resources

Joint Position Statement on Nutrition and Athletic Performance – American College of Sports Medicine, Academy of Nutrition and Dietetics and Dietitians of Canada