Whey protein and casein: an interesting combination for endurance sports
When practising endurance sports, the body has to sustain prolonged, intensive efforts. Above a certain level, physical activity can have an impact on our metabolism and lead to an imbalance between the breakdown and synthesis of muscle proteins.
The body is unable to synthesise all the amino acids necessary to maintain muscle mass. Among the twenty or so amino acids necessary for protein synthesis, nine ‘essential’ amino acids are not produced, or are produced in insufficient quantities to meet all the body’s needs.
It is therefore through our diet that we will obtain a sufficient supply of amino acids, and this involves consuming protein.
Proteins should represent between 10% and 20% of daily energy intake (Nutritional Reference for the Population – ANSES). However, the required energy intake varies depending on age, gender, the type of physical exercise and the duration of the effort.
For an endurance athlete who trains at least one hour, four to five times a week, protein intake should be between 1.1 g/kg/d and 1.6 g/kg/d
Therefore, according to current understanding, ANSES considers that between 0.83 g/kg/d and 2.2 g/kg/d of protein is sufficient for an adult under the age of 60 .
For an endurance athlete who trains at least one hour, four to five times a week, protein intake should be between 1.1 g/kg/d and 1.6 g/kg/d . An increase in frequency or duration of physical activity leads to higher energy requirements. For an athlete who trains intensively (more than two hours: six times a week), this level should be up to between 1.6 g/kg/d and 2 g/kg/d.
Quality and when to consume protein for endurance sports
For our body to be able to use this protein efficiently, it is important to consider the protein quality, but also the time it takes to digest, and its biological value.
Concerning protein quality, dairy protein has a remarkable essential amino acid profile, particularly for leucine.
Time necessary to digest protein: slow and fast digesting proteins
Whey and casein proteins have specific structures that affect the metabolism in different ways.
- Whey is a fast-digesting protein; amino acids such as leucine are released into the body sending a signal to stimulate muscle synthesis. ‘Fast’ proteins such as whey are therefore preferred after exercise to improve recovery.
- Casein, on the other hand, is digested more slowly in the stomach. The amino acids are released more progressively allowing the body to benefit from a regular source of protein.
Protein and a feeling of satiety
Several studies show that enhancing a meal with protein leads to greater satiety. For long-term efforts, as is the case for endurance sports, not feeling hungry is one of the keys to success.
Thanks to their amino acid profile and their digestion kinetics, proteins have an impact on the feeling of satiety , and the effect of dairy proteins is higher than that of other proteins . When the body digests protein, in addition to the amino acid intake, it sends a satiety signal to the hypothalamus, the area of the brain that regulates appetite.
Consuming good-quality protein helps to overcome the hunger pangs that athletes may experience when training for prolonged periods.
Biological value of protein
The quality of a protein is determined by its biological value. The biological value of a protein depends on its amino acid profile but also its postprandial bioavailability, in other words, its digestibility. For an activity such as an endurance sport, this criterion should be considered when deciding which proteins to consume as it will determine the body’s efficiency to assimilate and use them.
Dairy proteins are either high or excellent quality which contributes to maintaining muscle mass
To determine this biological value, several different scores are used. The two main scores used are the DIAAS (Digestible Indispensable Amino Acid Score) and the PDCAAS (Protein Digestibility Corrected Amino Acid Score). The DIAAS is the method chosen by the FAO (United Nations Food and Agriculture Organization) to replace the historical protein classification standard (PDCAAS).  
Proteins can be classed using quality categories based on the DIAAS value:
- <75: no quality claim
- 75–99: high-quality protein
- ≥ 100 excellent quality protein
Generally, dairy proteins are either high or excellent quality which contributes to maintaining muscle mass.
When to consume proteins
In our diet, we naturally consume protein throughout the day.
In the case of sports where a specific protein intake is required, studies show that the time of consumption has an impact on metabolism and on the feeling of hunger.
Consequently, the consumption of ‘fast’ proteins such as Whey immediately and up to two hours after an effort will contribute to the muscle mass recovery and maintenance process .
As caseins are ‘slow’ proteins, they should be consumed throughout the day or before bedtime to limit muscle breakdown during overnight fasting.
For prolonged effort (several hours), it is possible to supplement carbohydrate intake with protein to limit hunger pangs.
 ANSES Actualisation des repères du PNNS – Révisions des repères relatifs à l’activité physique et à la sédentarité (ANSES PNNS reference update – Review of references relating to physical activity and sedentary lifestyle) https://www.anses.fr/fr/system/files/NUT2012SA0155Ra.pdf
 Besoins protéiques du sportif d’endurance de loisir et de compétition (CERIN) (Protein requirements for endurance sports for leisure and competition) https://www.cerin.org/wp-content/uploads/2017/01/besoins-proteiques-sportif-endurance-loisir-competition.pdf
 Gilles Fromentin, Nicolas Darcel, Aurélie Lesdema, Rojo Rasoamanana, Catherine Chaumontet, et al. Protéines laitières et satiété, contrôle du comportement alimentaire (Dairy proteins and satiety, controlling eating habits). Innovations Agronomiques, INRAE, 2011, 13, pp.57-70. ffhal-01000370f. In French.
 Burd, N.A., Beals, J.W., Martinez, I.G., et al. Food-First Approach to Enhance the Regulation of Post-exercise Skeletal Muscle Protein Synthesis and Remodeling. Sports Med 49, 59–68 (2019). https://doi.org/10.1007/s40279-018-1009-y
 Dietary protein quality evaluation in human nutrition report of an FAO Expert Consultation https://www.fao.org/ag/humannutrition/35978-02317b979a686a57aa4593304ffc17f06.pdf
 Protein and amino acid requirements in human nutrition – Report of a Joint WHO/FAO/UNU Expert Consultation http://apps.who.int/iris/bitstream/handle/10665/43411/WHO_TRS_935_eng.pdf;jsessionid=830EA5E5D512DA8058AA6975969ED550?sequence=1
 Kerksick, C.M., Arent, S., Schoenfeld, B.J. et al. International society of sports nutrition position stand: nutrient timing. J Int Soc Sports Nutr 14, 33 (2017). https://doi.org/10.1186/s12970-017-0189-4
*Proteins help maintain muscle mass, increase muscle mass, and maintain normal skeletal structure.