Endurance training: which role for proteins?

A protein intake in addition to a carbohydrate intake is important following an intense endurance effort. This is known from several studies that have compared it to a simple intake of carbohydrates. Why is it effective? The muscle’s immune and inflammatory response to exercise is then improved, which limits the onset of muscle damage and pain.


Illustration with a study1: Post-exercise ingestion of carbohydrates + protein (0.8g per kg per hour of carbohydrates + 0.4g.kg.h of protein) improved tomorrow’s performance compared to ingestion of carbohydrates alone (1.2g.kg.h): ~63min vs. 50min on a 72% VO2max exhaustion test.

Despite this positive finding, the effects of repeated intake of carbohydrates + proteins are still poorly known during an intense training period – even though this is precisely the type of program athletes endure…



These periods of intensive training impose unusual physiological stress on the body. Therefore, the challenge of a better tolerance of the body to overload thanks to an adapted nutritional plan will be to limit this stress to facilitate the recovery phase in-between training sessions. So why are these proteins so important?

nutrition protéines période de surcharge– Firstly because a carbohydrate intake only does not stop the protein breakdown initiated during exercise, even if the recommendations are followed (for info: 1.2g.kg.h of carbohydrates for ~3-4h as soon as exercise stops, then 8-9g.kg spread over the rest of the day).

– Then because the difference between the protein ‘degradation’ and ‘synthesis’ is ~5g per hour of exercise (and more if the carbohydrate level is low). The protein balance thus quickly becomes negative in the event of prolonged effort, which then leads directly to the degradation of amino acids (ie. proteins that structure muscle (leucine, valine, alanine, glutamate) to produce energy.


1, 2, 3 POINTS.

Today, if we make the count on studies that have looked at the benefits of using protein + carbohydrates on endurance performance in periods of overload (compared to carbohydrates alone), the results are inconsistent. Benefit? No effect? To be continued… But having said that, several points still deserve to be raised.

1- First a quantitative point.

There is a dose-response relationship between protein intake and performance: this means that intake must be proportional to increased training load to produce results. Look why:

– In a first study2, +104g protein per day (3.0 g.kg.d) reduced the performance decline of trained cyclists after 7 days of overload compared to a control diet (1.5 g.kg.d).

– However, in another study3, ~67g.d of protein was insufficient to improve performance after 10 days of overload compared to a carbohydrate drink.

This ‘dose-response’ phenomenon is therefore noticeable in trained individuals. But it also depends on the basic nutritional diet! Indeed, a carbohydrate + protein diet will have more effects in individuals whose usual protein intakes are low (<~1g.kg.j). In the same logic, the reverse is also true: a protein ceiling exists so that proteins ingested in excess of the body’s ability to assimilate them are no longer stored but oxidized.


2- Then a qualitative point.

It must be known that protein synthesis decreases when one is at exercise (by ~40% after 2 hours of exercise at low intensity). But things are reversed in recovery: protein synthesis is reactivated to meet the needs of energy response and muscle restructuring. This reactivation is then opportune to assimilate more effectively the nutrients provided: we talk about a “metabolic window” which is ideal in the 30′ post-exercise and then dissipates in the 2h. You can see that this window is particularly interesting when 2 trainings are performed a few hours apart.

Always in a concern to optimize recovery, protein synthesis is maximized by the combined intake of carbohydrates + protein + leucine. This effect is certainly due to a higher concentration of plasma insulin which inhibits proteolysis. Therefore, leucine supplementation (e.g. parmesan, soy, cooked tuna/hen/beef, peanuts) of ~0.1g.kg.h is advisable when overloading. On the other hand, protein supplementation loses a lot of its benefits when it is no longer combined with carbohydrate intake !


3- Finally a physiological point.

At the level of the body, we notice an increase in the volume of plasma (in the blood) following a prolonged supplementation in carbohydrates + proteins. This is not observed under carbohydrate alone conditions (certainly due to the increase in plasma albumin concentration, favourable to water retention). This plasma expansion will have a positive impact on:

Systolic ejection volume: an increase in the amount of blood sent at every heartbeat;

Temperature regulation: greater vascularization of the cutaneous vessels = better dissipation of heat from the body to the environment = lower rise in internal temperature during exercise = lower risk of overheating.

In addition to this vascular effect, a protein equilibrium during periods of overload has a positive influence on muscle morphology and function by:

– Limiting muscle strain during exercise and reducing muscle volume after overload (a phenomenon frequently observed in endurance athletes);

– Stimulating protein synthesis, which helps maintain or even increase strength qualities.


Protéines 3WHAT ELSE?

Today, when we talk about protein and training, an average recommendation is to recommend ~20g of protein in recovery if the training has been intense. What we know less is that a moderate intake (>10g) is also recommended 30′ before bedtime in order to preserve the protein balance during the night (since we don’t have any more intake for several hours!). In the same logic, a moderate protein intake is recommended as soon as you get up.

During the day, endurance athletes are therefore advised to eat an average of at least 1.5-1.7g.kg of protein. In terms of the nature of the proteins ingested, it is less precise: it does not seem to influence the performance response. However, we now know that it is preferable to opt for animal proteins rather than vegetable proteins because of their digestibility and their higher leucine content.

To go further: 1Rustad et al. 2016 ; 2Witard et al. 2011 ; 3D’Lugos et al. 2016