Protein for endurance: sleep on it!

Protein has long been the favored macronutrient for strength and power athletes to promote muscular adaptation, with much less emphasis on optimizing carbohydrate intake. By contrast, endurance athletes have long emphasized carbohydrate intake, and to a lesser extent fat intake, to maximize energy availability during performance, with less emphasis on protein intake and maximizing muscular adaptations.  Based upon the different physiological demands and the adaptations that these two groups of athletes require, this makes sense.

Protein, muscle and sleep

Strength and power athletes are renowned for pursuing every nutritional avenue to enhance muscle growth. One of the strategies that emerged many years ago was the notion of consuming protein just prior to sleep. The thought process was that because no nutrients would be ingested during overnight sleep, there would be a significant period of time where the blood level of amino acids (the building blocks of proteins) would run low, which could result is less muscle growth following the previous day’s training.

To counter this, strength and power athletes would typically consume a large dose of protein prior to sleep in the hopes of keeping amino acid levels elevated through the night. It turns out that this intuition proves to be true. Research has since shown that consuming protein just prior to bed can enhance the skeletal muscle adaptive response to hard training⁽¹⁾.

Endurance and protein

Initially, these finds were largely ignored by the endurance community as athletes and coaches were not principally looking to optimize the muscular response to training. Rather than seeking larger and stronger muscles, improving sustainable endurance performance was the goal. At the same time however, there has been a growing recognition that protein is important for endurance athletes as well. After all, it is the muscles that do all the work. Further, it is recognized that the enzymes and mitochondrial structures (the ‘energy factories’ within muscle cells) responsible for great endurance performance are made of proteins as well. Importantly, research has demonstrated that the ingestion of protein can positively impact mitochondrial protein synthesis after exercise⁽²⁾.

It is the convergence of these two lines of thought that brings us to the research we’ll examine in this article. Pre-sleep protein has shown to enhance muscle protein synthesis, and protein ingestion has been shown to enhance the mitochondrial response to exercise training. Given these facts, can pre-sleep protein ingestion enhance mitochondrial protein synthesis following endurance exercise? This is the question a recent study sought to answer. 

The research

A research group based in the Netherlands gathered together 36 subjects for this study^(3). Two hours after consuming a light dinner, the subjects performed a 60-minute endurance exercise bout. Immediately afterwards, all subjects consumed a beverage containing 49 grams of carbohydrate. Then approximately three hours later, and just prior to sleep, the subjects consumed one of three different drinks:
•    A zero calorie drink
•    A drink containing 45 grams of casein (a slow digesting milk protein)
•    A drink containing 45 grams of whey (a rapid digesting milk protein)

This final pre-sleep drink was the only difference between the protocols performed by the athletes.

The researchers examined different markers to fully understand the impact of the three pre-sleep drinks. They looked at differences in the blood levels of phenylalanine and leucine, two important amino acids. They also checked for differences in total amino acid and essential amino acid levels. Most importantly, they examined differences in muscle protein synthesis and mitochondrial protein synthesis between the different groups.

What they found

Unsurprisingly, the amino acid levels in the blood were significantly elevated in subjects who ingested either type of protein, whereas no change was shown in the control group. The elevation of essential amino acids and total amino acids was similar between the two types of protein. However, there were differences in phenylalanine and leucine elevations between the two types of protein. Phenylalanine was more dramatically elevated in the casein group whereas leucine was significantly elevated in the whey group, which may explain the following result.

When it came to muscle and mitochondrial protein synthesis, protein ingestion resulted in elevated rates in both groups compared to the control. However, whey protein consumption was more effective than casein in this regard (see figure 1). This may be related to the more substantial elevations in leucine, which has been shown to be a potent simulator of protein synthesis. Importantly, there were no differences in subjective markers of sleep quality in any of the groups, indicating no negative impact of protein ingestion on sleep.

Figure 1: Muscle and mitochondrial protein synthesis rates