Protein intake in endurance sports

CORTINA D'AMPEZZO, ITALY - MAY 24: Simon Yates of United Kingdom and Team BikeExchange, Gorka Izagirre Insausti of Spain and Team Astana – Premier Tech & Aleksander Vlasov of Russia and Team Astana – Premier Tech during the 104th Giro d'Italia 2021, Stage 16 a 153km stage shortened due to bad weather conditions from Sacile to Cortina d'Ampezzo 1210m / @girodiitalia / #Giro / on May 24, 2021 in Cortina d'Ampezzo, Italy. (Photo by Tim de Waele/Getty Images)
Courtesy of:
Dr. Luca Pollastri
Specialist in Sports Medicine
Medical Doctor Team Bike Exchange

The consumption of an adequate amount of protein has long been considered strategic to supporting the performance of sportsmen and women, particularly in activities requiring large muscle masses. We have reports of athletes who, since the first Olympics, used to modify their diets by introducing large quantities of meat for this purpose; now, thanks to numerous scientific studies, the methods of nutrition and supplementation have developed considerably. 

Proteins are macromolecules composed of a large number of amino acids, involved in numerous processes of cellular life with various functions including the structural and mechanical functions of muscles. They differ in terms of their amino acid content, which characterises them in qualitative terms, as the body is unable to synthesise all the existing amino acids, which must therefore be taken from the diet (phenylalanine, threonine, tryptophan, methionine, lysine, leucine, isoleucine and valine). The last three of these amino acids are known to many athletes as branched-chain amino acids (BCAA).

Traditionally, athletes involved in endurance sports consider the use of protein to be less important than that of carbohydrates. However, the correct intake of proteins in terms of quantity and timing is essential for any sport, whether endurance, strength or mixed. 

This is explained by the fact that an increase in injuries and subsequent regeneration of new contractile fibres occurs every time we carry out medium to heavy physical activity of whatever nature. This is why we should not consider protein intake to be useful for directly increasing performance, but rather for other functions related to muscular efficiency and body composition, especially in the medium and long term. 

Several scientific societies, including the American College of Sports Medicine, recommend a protein intake for athletes of between 1.2 and 2g/Kg/day, suggesting consumption close to the upper limits of this range for athletes engaged in strength activities and slightly lower for endurance athletes. This represents an intake ranging from 150 to 250% of the recommended intake for sedentary people (0.8g/Kg/day). 

Intakes higher than this seem to have a role limited to specific situations that require personalised assessments in order to obtain a real benefit. 

Athletes who are used to very long training sessions and races or races with significant eccentric muscular activity (marathons, sky races, long-distance cycling, etc.) are at greater risk of experiencing a catabolic state, i.e. a reduction in muscle mass due to tissue damage. If tolerated, these athletes should try to take a pre-exercise dose of protein of 0.3g/kg and a post-exercise dose of 0.25g/kg/hour (in combination with carbohydrates). This strategy is known to reduce blood markers of muscle injury, reduce post-exercise muscle fatigue and help maintain a good daily protein balance. 

It is also known that muscle synthesis is stimulated for at least 24 hours after exercise and that this represents an ideal window in which the body is able to absorb and utilise what it gets from the diet.

Post-exercise protein intake is of particular interest as it not only plays a role in the body’s ability to regenerate muscle mass but, in the case of sub-optimal carbohydrate intake, is able to increase the synthesis of muscle glycogen (our energy stores) through mechanisms linked to better use of certain hormones involved in the process of using and storing sugars. Introducing 20-25g of protein immediately post-exercise and then every 2-3 hours can therefore have a dual role in terms of recovery in preparation for subsequent efforts. 

At the end of the phase immediately following exercise, the use of slow-digesting proteins in the evening, including caseins, ensures the presence of a discrete amino acid pool in the bloodstream throughout the night, capable of supporting protein synthesis even during the hours of overnight fasting. It has also been shown that they are able to support lipolysis and fat oxidation, thus providing a positive action in achieving optimal body composition.

So which proteins should be used? In qualitative terms, there are different ways and scales for comparing types of protein. Focusing on the endurance athlete, there are two key points to focus on: the amount of leucine and the digestion/absorption kinetics. In general, the proteins with the highest leucine content are those derived from dairy products (9-11%), eggs (8.6%) and meat (8%). Vegetable proteins have lower percentages, so a specific assessment in terms of requirements should be made when using only these protein sources. In terms of supplementation, Egg, Whey, Casein and Soy Proteins are better able to stimulate protein synthesis than the use of individual amino acids. In particular, Whey Proteins, due to their content of essential amino acids, solubility and excellent assimilation kinetics, appear to be the most suitable for supplementation. The role of branched-chain amino acids, which has recently been reviewed in terms of their usefulness for protein synthesis, could be re-evaluated in endurance performance by assessing their role in counteracting the production of certain endogenous molecules that act as signals of fatigue in the brain. 

Here are some examples of high protein foods whose intake provides 10g of protein: 2 small eggs – 300 ml of cow’s milk – 20 g of skimmed milk powder – 30 g of cheese – 200 g of yoghurt – 35-50 g of meat, fish or chicken – 4 slices of bread – 90 g of breakfast cereal – 2 plates of pasta – 400 ml of soya milk – 60 g of nuts or seeds – 120 g of tofu or soya meat – 150 g of pulses or lentils – 200 g of beans – 150 ml of fruit smoothie.

Although several studies have shown that protein intake is safe, some athletes are afraid of the possible negative effects on certain organs, including the liver and kidneys. Many of these fears stem from the fact that patients with kidney failure have to eat a diet low in protein. This does not justify healthy athletes with no evidence of organ damage needing to pay special attention to the amounts outlined above. Even the World Health Organisation has recently clarified that there is no known correlation between high-protein diets and kidney disease.

Given this, in order to avoid the possibility of protein deprivation leading to weakening and subsequent tissue damage, it is reasonable to advise athletes to eat a diet high in protein rather than low in it.