It's about synergy
As mentioned earlier, macronutrient intake modulates post-exercise protein synthesis in ways that are just beginning to be understood. Yes, protein is required to supply essential amino acids for protein synthesis, but what is the mechanism by which protein is controlling this process? Also, are carbohydrates and fats needed only for fuel replacement, or do they play an "interactive" role in post exercise protein synthesis? Recent research has shed light on these questions.

Researchers from the Division of Nutritional Sciences at the University of Illinois examined the effect of post exercise meal composition on protein synthesis. To do this, they looked specifically at the activity of specific proteins known to regulate protein synthesis at the translational level.

Initiation of translation (the binding of mRNA to the ribosomal pre-initiation complex) requires group 4 eukaryotic initiation factors (eIFs). These initiation factors interact with the mRNA in such a way that makes translation (the construction of new proteins from the mRNA strand) possible. Two eIFs, called eIF4A and eIF4B, act in concert to unwind the mRNA strand. Another one called eIF4E binds to what is called the "cap region" and is important for controlling which mRNA strands are translated and also for stabilization of the mRNA strand. Finally, eIF4G is a large polypeptide that acts as a scaffold or framework around which all of these initiation factors and the mRNA and ribosome can be kept in place and proper orientation for translation.

The researchers in this study looked at the association of the mRNA cap binding protein eukaryotic initiation factor-4-E (eIF4E) with the translational inhibitor 4E-eukaryotic initiation factor binding protein-1 (4E-BP1) in the acute modulation of skeletal muscle protein synthesis during recovery from exercise. Fasting male rats were run on a treadmill for 2 h at 26 m/min and were fed immediately after exercise with saline, a carbohydrate-only meal, or a nutritionally complete meal using Ensure Powder (54.5% carbohydrate, 14% protein, and 31.5% fat). Exercised animals and non-exercised controls were studied 1 h post-exercise.

Muscle protein synthesis decreased 26% after exercise and was associated with a fourfold increase in the amount of eIF4E present in the inactive eIF4E.4E-BP1 complex and a concomitant 71% decrease in the association of eIF4E with eIF4G. Refeeding the complete meal, but not the carbohydrate meal, increased muscle protein synthesis equal to controls, despite similar plasma concentrations of insulin. Additionally, eIF4E.4E-BP1 association was inversely related and eIF4E.eIF4G association was positively correlated to muscle protein synthesis. This study demonstrates that recovery of muscle protein synthesis after exercise is related to the availability of eIF4E for 48S ribosomal complex formation, and post-exercise meal composition influences recovery via modulation of translation initiation.

The results of this study tell us a few things:

1. Insulin (via carbohydrate intake) alone is not enough to prevent 4E-BP1 from sequestering eIF4E. EIF4E must be free to bind to eIF4G in order for protein synthesis (i.e. recovery from training and net muscle growth) to begin. Insulin as well as amino acids must be present at the same time as indicated by the results from the group that were fed a mixed nutrient meal. So although feeding of the carbohydrate meal resulted in elevated blood glucose and elevated insulin levels, carbohydrates alone are not sufficient to allow protein synthesis to begin.

2. The only group that experienced a significant drop in cortisol levels was the mixed meal group. The carbohydrate-only group showed that neither blood glucose nor insulin had any effect on reducing cortisol levels. In contrast, the mixed meal group showed cortisol levels even below those in the control group who did no exercise and were also fed the same meal.

It would have been nice for the authors of this experiment to explore the effect of the fat content in the "mixed meal". From the results we saw that cortisol was lower in the mixed meal group. We can only speculate whether this was due to the protein, the fat, or some combination of protein, fat and carbs. Further research in this area should take into consideration all components of the post exercise meal. One other issue that might be addressed in humans is the time frame during which re-alimentation is critical to "long term" adaptation to exercise.

In closing...

Pre- and post-exercise nutrition is critical if one wants to maximize the anabolic effects of exercise. The pre-exercise meal should be high in a quickly digestible protein. This will ensure high delivery of amino acids to the muscle tissue. Carbohydrates can also be taken in to minimize glycogen loss and suppress catabolic hormones. Fat should be avoided pre-exercise unless the exercise is for endurance.

The post exercise meal should consist of carbohydrate, protein and perhaps a small amount of essential fats, in a form that is easily and quickly digestible. There are many meal replacement products that fit the bill. Just pick the one you like the most. Don't worry about sugar content because right after a workout, fat storage is not a big issue. A liquid meal is the most practical method of post-exercise feeding although it is probably not essential. The ratio of macronutrients depends somewhat on the nature of the training session. An emphasis on high glycemic carbs, complete readily digestible proteins such as whey, egg, or high quality casein, and essential fats such as fish or flax oil will meet the criteria for an effective post exercise meal.

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