Protein Intake in Sports Practice

Introduction

Proteins are an indispensable component for the normal functioning of the body, in which they play numerous roles: metabolism, structure, and/or transport. Within the skeletal muscle, they form myofibrils, which are the structures responsible for muscle contraction.

In the sports context, the ability of athletes to produce adequate movement is crucial for their performance, and therefore, the development and/or maintenance of suitable skeletal muscle mass is paramount. Consequently, the daily protein intake must be adapted based on the discipline and performance level of the athletes, such as increasing muscle mass in preparation for a competition or maintaining it during “off” periods throughout the season.

To maintain normal body functioning and normal muscle mass, the WHO recommends a minimum daily intake of 0.8 to 1.0 g/kg(weight)/day for the entire population. However, several recent studies have shown the emergence of resistance to the anabolic stimulus of protein intake in older people¹. In fact, Moore et al. showed that to induce identical muscle protein synthesis, an older man had to ingest 0.40 g/kg(weight) of proteins during a meal compared to 0.24 g/kg(weight) for a young man. These results led several teams to continue these investigations, especially in women²,³, showing that the minimum recommended intake for older people was underestimated by 30 to 50%. These findings led several authors to recommend a daily protein intake of 1.2 g/kg(weight)/day, well distributed throughout the day with a minimum of 3g of leucine per intake, for people over 60 years old with the aim of maintaining normal muscle mass⁴.

This example observed in older people clearly demonstrates that it is necessary to adapt protein intake to the population according to its characteristics, especially its sports practice.

Protein Intake in Athletes

As mentioned earlier, it is necessary to adapt the protein intake of an athlete based on two factors: their sports practice and their goals, either long-term or during the season, which can be either an increase or maintenance of skeletal muscle mass. In both cases, the goal is to provide a sufficient amount of amino acids to create new myofibrils, generating hypertrophy, or to prevent myofibrils from degrading in order to supply the necessary amino acids for the organism’s functioning.

Since 2017, the International Society of Sports Nutrition recommends a daily protein intake of 1.4 to 2.0 g/kg(weight)/day in order to increase muscle mass or at least maintain it⁵. Furthermore, in the specific case of strength-trained athletes, such as weightlifters or rugby players, it recommends an intake of 2.3 to 3.1 g/kg(weight)/day to maintain their muscle mass during hypocaloric phases.

Although these recommendations are suitable for athletes, they do not distinguish between the daily protein intake adequate for maintaining muscle mass and that necessary for gaining muscle mass. In a meta-analysis conducted in 2018 that compiled 49 studies, Morton et al.⁶ demonstrated that the gains in muscle mass associated with protein intake increased between 0.9 and 1.6 g/kg(weight)/day, before reaching a plateau from 1.6 g/kg(weight)/day (Figure 1). In other words, an athlete with an intake of between 0.9 and 1.6 g/kg(weight)/day will see a more significant increase in muscle mass as their protein intake increases, while from 1.6 g/kg(weight)/day to 2.2 g/kg(weight)/day, the gains in muscle mass will be similar for the same resistance training.

Figure 1: Graph showing the gain in fat-free mass (ΔFFM) as a function of daily protein intake. Extracted from Morton et al. 2018⁶.

Therefore, the authors of this study recommend a daily protein intake between 1.6 and 2.2 g/kg(weight)/day with the goal of maximizing muscle mass gains induced by resistance training. Consequently, in the context of sports that require significant resistance training (for example, weightlifting), it is advisable to suggest this protein intake in order to maximize the athletes’ muscle mass.

Traditionally, an increase in protein intake is often present in sports that require a high level of resistance training and less so in endurance sports. Indeed, performance in endurance sports is primarily based on the ability of carbohydrates and fats to provide energy during effort, with these two macronutrients being the most monitored in these athletes. However, it appears that approximately 20% of the energy supplied during an endurance exercise comes from proteins⁷, thus significantly increasing the daily protein needs. Therefore, a daily intake of between 1.4 and 2.0 g/kg(weight)/day is also recommended to prevent muscle proteins from being consumed to compensate and thus maintain the muscle mass of athletes trained in endurance⁸.

Since up to 20% of the energy supplied during exercise comes from proteins, it is legitimate to wonder if an adapted protein intake during effort could improve performance, through a higher energy contribution from proteins. Several studies have been conducted to answer this question, and protein intake during exercise does not increase performance⁵ but it seems that an intake of 0.25g/kg(weight)/hour can reduce muscle damage induced by exercise⁸.

In conclusion, athletes need a higher protein intake than WHO recommendations with doses of:

• 1.6 to 2.2 g/kg(weight)/day to increase muscle mass
• 1.4 to 2.0 g/kg(weight)/day to maintain muscle mass

Increase in Protein Intake and Kidney Functions

A barrier to increasing daily protein intake in athletes could be a progressive degradation of kidney filtration function. Indeed, a specific increase in protein intake causes an increase in renal filtration flow⁹, which would progressively damage the kidneys. This has been observed especially in individuals who already present moderate renal insufficiency or comorbidities that favor the appearance of renal insufficiency, such as arterial hypertension¹⁰.

In a study conducted on resistance-trained men, Antonio et al. ¹¹,¹² demonstrated that a daily intake greater than 3 g/kg(weight)/day for a year did not alter creatinine levels, thus indicating the absence of kidney damage. However, cases of renal failure have been previously observed in bodybuilders¹³, which could suggest a detrimental effect of high daily protein intake on renal function. This result, however, must be nuanced considering that the daily protein intake of these bodybuilders was between 4 and 30 g/kg(weight)/day, which is up to 10 times the intake used in the publication by Antonio et al.! Moreover, many of the reported cases are associated with creatine supplementation 22 times higher than the maximum recommended intake, the use of anabolic steroids, and diuretics at the time of competitions. These three factors can also severely damage the kidneys, making it extremely difficult to conclude that protein intake alone is responsible for the renal damage observed in these bodybuilders.

In conclusion, the current recommendations for an adequate protein intake in athletes do not cause kidney problems while providing benefits in body composition. The observed cases of renal insufficiency seem to be related to the combination of several factors:

• A daily protein intake associated with creatine supplementation in doses much higher (between 10 and 22 times) than the maximum recommended,
• the use of anabolic steroids, aimed at hypertrophy, and diuretics, aimed at dehydration, both of which are considered doping substances.

Conclusion

Given their sports practice, athletes need a daily protein intake higher than the daily recommendations for the general population in order to 1) maintain their skeletal muscle mass, with an intake of 1.4-2.0 g/kg(weight)/day, or 2) gain skeletal muscle mass, with an intake of 1.6-2.2 g/kg(weight)/day. In healthy individuals, these intakes higher than the recommendations do not seem to carry risks at the renal level, although it is important to pay attention to the presence of comorbidities in the case of amateur athletes.

References

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