Intro
Dietary intake of protein is the vital source of essential amino acids, and a sufficient intake is needed to ensure a balance in protein turnover in order to maintain the protein pool of the body. For older adults, the dietary intake of protein has shown to be skewed towards the evening meal, with less protein consumed at breakfast and lunch. Resultingly, at some daily meals the protein turnover is suboptimal stimulated, while at the evening meal all dietary amino acids may not be utilized.
 
Aims
The aim of the present study was to explore if a more even distribution of the dietary protein could improve the dietary amino acid utilization and the subsequent anabolic protein synthetic response and protein turnover net-balance.
 
Methods
A total of 24 healthy elderly men and women (65-80 years of age) were included in a randomized controlled trial. Seven days of habituation to either an EVEN (n=12) or SKEWED (n=12) protein intake, was followed by a 4-day trial that was initiated by an oral intake of D2O to measure integrated muscle protein synthesis (MPS) over the initial 3-day trial period. Through the entire trial period all meals were served with intrinsically 2H5-phenylalanine labeled meat as the primary protein source, thereby enabling an assessment of the dietary amino acid utilization. Plasma 2H-alanine and muscle protein bound, 2H-alanine and 2H5-phenylalanine enrichments were measured by mass spectrometry from daily blood samples and vastus lateralis muscle biopsies taken at baseline and at the end of the 3-day trial period. Lastly, an acute trial was conducted on the fourth trial-day where an infusion of 2H8-phenylalanine and 2H2-tyrosine was used to measure whole body protein turnover from blood samples taken throughout the day under influence of the EVEN or SKEWED dietary distribution. All subjects gave their written consent to participate in the protocol, and the study adhered to the Declaration of Helsinki and was approved by the Ethics Committee of Copenhagen and Frederiksberg (H-18026529).
 
Results
During the 3-day trial period the MPS was not different between EVEN (2.16 +/- 0.46 %/hour) and SKEWED (2.23 +/- 0.32 %/hour), and the muscle protein bound 2H5-phenylalanine enrichment was the same in EVEN (0.0049 +/- 0.0013 MPE%) and SKEWED (0.0054 +/- 0.0010 MPE%). During the acute trial, protein turnover net-balance was more positive in EVEN after breakfast and lunch compared to SKEWED and was the same in both groups after dinner.
 
Conclusion
A dietary protein intake with either and EVEN or SKEWED distribution pattern resulted in identical muscle protein synthesis and amino acid utilization when measured over 3 days. Yet, fluctuations in whole body protein net-balance were seen throughout the acute trial day, with a greater net-balance in EVEN.