Most contemporary sports scientists can testify that high intensity interval training is a proven and effective means of improving performance. But one of the major drawbacks with this type of training is that it can reduce immunity and increase the risk of upper respiratory tract infections. Given that amino acids and protein serve as important substrates for cells of the immune system, it makes sense that sports scientists would want to test the effect of increased protein intake on immune function. As such, a group of researchers from UK, USA, Germany and The Netherlands set out to determine whether dramatically increasing protein intake could prevent the drop in immune function following a week of high intensity training in high performance cyclists.
Researchers compared immune function after a week of normal training and a week of high intensity training. During the week of high intensity training, one group was randomly allocated to receive additional protein, while the other group consumed a diet that was equivalent in calories to the high protein group. More specifically, the high protein group consumed a diet providing 3.0g per kilogram bodyweight, which was double that of the control group (i.e. 1.5g/kg bodyweight). Importantly, the additional protein was provided in the form of 3 x 20g serves of a specialised casein protein hydrolysate called PeptoPro®.
What makes this study particularly interesting is that 3.0g/kg is a level of protein intake typically reserved for extreme bodybuilders or strength athletes. Most endurance athletes would consider such a protein intake too high or even toxic. But this landmark study suggests that during periods of high intensity training, a protein intake of 3.0g/kg can prevent the normal drop in immune function in elite endurance athletes normally associated with such training. The absence of infection is one of the most crucial factors in being able to maintain consistent training and improve performance.
One drawback about the study was that the authors did not discuss how the unique type of protein powder used may have affected the outcome. PeptoPro® is a very unique casein hydrolysate protein in terms of its composition. It is the only protein powder that claims to have a minimum 60% content of di- and tri-peptides. As such, it contains one of, if not, -the highest level of di- and tri-peptides of any milk-based protein powder. This aspect of the protein powder was not discussed as a possible mediating factor in the study’s results. It remains to be seen whether the same results would be seen with a good quality whey protein hydrolysate protein powder, or even a blended whey protein for that matter.
Witard OC, et al. High dietary protein restores overreaching induced impairments in leukocyte trafficking and reduces the incidence of upper respiratory tract infection in elite cyclists. Brain, Behavior, and Immunity. 2014;39:211-219.