From the Lab: Protein and amino acids requirements for athletes - PART 2; why timing is important!

Tue 08 Jun 2010

A further area of interest in the effects of protein intake, is that of the timing of protein consumption. Our previous article discussed the research surrounding protein requirements by athletes. In this article we'll establish when protein intake is so crucial, how to maximise protein uptake, and what factors to consider to ensure recovery, growth and performance are all optimised.

A particular study by Rasmussen (2000) involved the direct measurement of protein sysnthesis. The study used subjects involved in intense resistance training on two seperate occasions. Subjects were given a solution of amino acids (AA) (the building blocks of protein) and sucrose (a sugar) in 500ml water at either 1 or 3 hours post exercise. The study showed that muscle protein synthesis and net balance were increased when the protein/carbohydrate solution was ingested at either 1 or 3 hours after exercise. Therefore in terms of this time difference, it didn’t seem to matter at which time the solution was taken, and furthermore it showed that a relatively small amount of AA was able to induce the increase in protein synthesis.

The use of protein supplements following exercise is a heavily studied area, with benefits to muscle recovery and growth well established. In addition to these apparent benefits of protein ingestion following exercise, it has also been suggested that protein intake prior to exercise may be important.

Tipton et al (2001) studied whether ingestion of AA before exercise affected protein balance. I.e. could it prevent protein breakdown during exercise, and furthermore promote protein synthesis during exercise. They measured arteriovenous phenylalanine concentration (amino acid concentration of the blood) with both immediately pre and post AA intake. The study used 6 subjects, involving a similar protocol and measurement collection as that of Rasmussen (2000). They showed that arteriovenous phenylalanine concentrations increased during exercise in the PRE trial, and increased after exercise in both PRE and POST trials. Furthermore muscle phenylalanine, i.e. AA taken up by the muscle, was higher with PRE ingestion. Understandably, net phenylalanine uptake across the leg was significantly greater in the PRE than POST trial, perhaps due to an increased AA availability. Therefore this study showed that taking AA before exercise showed to be better than post exercise alone, although both were beneficial. The results of this study indicate that protein synthesis was greater in the pre-exercise trial.

A series of studies completed by the same authors confirm these findings, and taken together suggest that the optimum time for ingestion of an essential AA & carbohydrate solution is immediately before exercise, perhaps due to an increased net phenylalanine uptake.

It has been shown that net muscle protein synthesis results from ingestion of essential AA alone. Thus it is clear that non-essential AA are not required for the stimulation of muscle protein synthesis.

Tipton et al (2007) investigated the effect of whole protein before exercise. They used a similar protocol to previous essential AA studies, but this time involved ingestion of a whey protein solution either immediately before or 1 hour post exercise, as well as an essential AA + carbohydratye solution. They showed that there was no significant difference between pre and post ingestion on phenylalanine concentration. There was a greater increase in concentration with the essential AA + carbohydrate mix, than whey protein alone. This could be due to differences in the rate of digestion or a lack of carbohydrate with the whey protein. This also leads to the question of what are the differences between supplementation of essential versus non-essential AA.

A study by Tipton et al (1999) showed that consumption of either an essential AA only, or mixed AA solution both resulted in an increased net protein balance. The essential AA solution produced an equal response to that of the mixed solution, suggesting that only essential AA are required. However the net protein uptake by the muscles was lower with essential AA alone, suggesting a mixed AA solution may be required for maximum efficiency of uptake. Further research is likely warranted into the preference of essential or mixed AA formulas.

We've discussed the apparent stimulation of muscle protein synthesis seen through ingestion of essential AA both before and after exercise. It is of interest as to by what process this increase is produced. Bohe et al (2003) studied exactly this. They found that prior to ingestion of essential AA following exercise, normal pathways of protein synthesis occur (though this may be out-balanced by protein degradation). Following ingestion of protein, and therefore increased AA concentrations in the blood, additional pathways are regulated and stimulated to have a direct stimulatory effect on protein synthesis within the muscle itself.

This area of nutrition, i.e. the effect of protein ingestion on protein balance before and after exercise, is still an emerging area. While recommendations of total protein intake are helpful, i.e. g/day, they are not the full story. Consideration should also be given to the timing of intake and composition of protein ingestion, with essential AA shown to be sufficient at inducing protein synthesis, and ingestion prior to exercise may increase this effect. Furthermore essential AA seem to be more important than non-essential AA, which will have a bearing on the food choices of athletes to consider this timing and type of protein intake. Mixed AA solutions may however be beneficial, perhaps due to an increased AA uptake by the muscle tissue. Ultimately, current theories of protein requirements for athletes may suggest that in those which dietary protein is low, essential AA supplementation may be beneficial, and a high-quality protein source both before and after exercise should be employed as a strategy. The resultant increased protein synthesis may be further augmented by the addition of carbohydrates alongside protein.

References

Rasmussen et al. (2000). An oral essential amino acid-carbohydrate supplement enhances muscle protein anabolism after resistance exercise. Journal of Applied Physiology, 88, 386-392.

Tipton et al. (2001). Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise. American Journal of Physiology, 281, E197-EE206.

Tipton et al. (2007). Stimulation of net muscle protein synthesis by whey protein ingestion before and after exercise. American Journal of Physiology, 292(1), E71-76.

Tipton et al. (1999). Postexercise net protein synthesis in human muscle from orally administered amino acids. American Journal of Physiology, 276, E628-E634.

Tipton K.D, Wolfe R.R (2004). Protein and amino acids for athletes. Journal of sports Sciences, 22, 65-79.

Bohe et al. (2003). Human muscle protein synthesis is modulated by extracellular, not intramuscular amino acid availability: a dose-response study. The Journal of Physiology, 552(Pt 1), 315-324.