Effects of Whey Protein Isolate Ingestion on Muscle Protein Synthesis at Rest and After Resistance-exercise in Middle-aged Men: A Research Protocol

Introduction: Sarcopenia is a syndrome primarily found in elderly individuals and is defined by decreased skeletal muscle mass and strength. Sarcopenia often increases the risk or is comorbid with various diseases. Thus, the objective of this study is to determine the appropriate dosage of whey protein isolate (WPI) for middle-aged men at rest and after resistance-exercise for maximum muscle protein synthesis (MPS) and to reduce the risk of sarcopenia. Methods: 50 healthy men (age 45± 5yrs, BMI < 30 kg/m2) will be randomly assigned an amount of ingested WPI (0g,10g,20g,30g,40g). 24 hours prior, a baseline saliva sample and ingestion of 5 doses of 150 mL bolus (70% D2O) every 2 hours will be completed at the participants’ own homes. On the day of the study, a saliva sample will be taken 1 hour before 10 repetitions of maximum unilateral leg extension. After the exercise protocol (t = 0 h), saliva samples will be obtained every hour until t = 6 h and 3 muscle biopsies at t = 0 h, t = 3 h, and t = 6 h. After isolating myofibrillar protein fractions from the biopsies, the samples will be analyzed using gas chromatography-pyrolysis-isotope ratio mass spectrometer (GC-P-IRMS). Analysing saliva samples will be conducted using temperature conversion elemental analyzer (TC/EA) followed by isotope ratio mass spectrometer (IRMS). Atom percent excess for both deuterium enrichment of protein-bound alanine and precursor enrichment will be conducted to allow the calculation of fractional synthetic rate (FSR, %/h). Discussion: We anticipate FSR (%/h) will be significantly greater in the exercised leg compared to the unexercised leg at each WPI ingestion dosage. Furthermore, we anticipate that ≥20 g of ingested WPI will be sufficient for maximal MPS at rest. Finally, we anticipate that at ≥30 g ingestion of WPI will be sufficient for maximal MPS after resistance training. It is beneficial for physicians to know the optimal dose for MPS in middle-aged adults, so they can suggest more accurate recommendations of proactive protein intake. This will help alleviate the high prevalence of sarcopenia and its detrimental effects on health, healthcare, and the economy.