title: Prolonged Adaptation to a Low or High Protein Diet Does Not Modulate Basal Muscle Protein Synthesis Rates - A Substudy.
abstract: BACKGROUND
  Based on controlled 36 h experiments a higher dietary protein intake causes a positive protein balance and a negative fat balance. A positive net protein balance may support fat free mass accrual. However, few data are available on the impact of more prolonged changes in habitual protein intake on whole-body protein metabolism and basal muscle protein synthesis rates.
  
  
  OBJECTIVE
  To assess changes in whole-body protein turnover and basal muscle protein synthesis rates following 12 weeks of adaptation to a low versus high dietary protein intake.
  
  
  METHODS
  A randomized parallel study was performed in 40 subjects who followed either a high protein (2.4 g protein/kg/d) or low protein (0.4 g protein/kg/d) energy-balanced diet (30/35/35% or 5/60/35% energy from protein/carbohydrate/fat) for a period of 12 weeks. A subgroup of 7 men and 8 women (body mass index: 22.8±2.3 kg/m2, age: 24.3±4.9 y) were selected to evaluate the impact of prolonged adaptation to either a high or low protein intake on whole body protein metabolism and basal muscle protein synthesis rates. After the diet, subjects received continuous infusions with L-[ring-2H5]phenylalanine and L-[ring-2H2]tyrosine in an overnight fasted state, with blood samples and muscle biopsies being collected to assess post-absorptive whole-body protein turnover and muscle protein synthesis rates in vivo in humans.
  
  
  RESULTS
  After 12 weeks of intervention, whole-body protein balance in the fasted state was more negative in the high protein treatment when compared with the low protein treatment (-4.1±0.5 vs -2.7±0.6 μmol phenylalanine/kg/h;P<0.001). Whole-body protein breakdown (43.0±4.4 vs 37.8±3.8 μmol phenylalanine/kg/h;P<0.03), synthesis (38.9±4.2 vs 35.1±3.6 μmol phenylalanine/kg/h;P<0.01) and phenylalanine hydroxylation rates (4.1±0.6 vs 2.7±0.6 μmol phenylalanine/kg/h;P<0.001) were significantly higher in the high vs low protein group. Basal muscle protein synthesis rates were maintained on a low vs high protein diet (0.042±0.01 vs 0.045±0.01%/h;P = 0.620).
  
  
  CONCLUSIONS
  In the overnight fasted state, adaptation to a low-protein intake (0.4 g/kg/d) does not result in a more negative whole-body protein balance and does not lower basal muscle protein synthesis rates when compared to a high-protein intake.
  
  
  BACKGROUND
  Clinicaltrials.gov NCT01551238.
authors.affiliation: Department of Human Biology, School of Nutrition and Translational Research in Metabolism, Maastricht University, Maastricht, The Netherlands.
authors.forename: Rick
authors.initials: R
authors.lastname: Hursel
authors.affiliation: Department of Human Biology, School of Nutrition and Translational Research in Metabolism, Maastricht University, Maastricht, The Netherlands.
authors.forename: Eveline A P
authors.initials: EA
authors.lastname: Martens
authors.affiliation: Department of Human Biology, School of Nutrition and Translational Research in Metabolism, Maastricht University, Maastricht, The Netherlands.
authors.forename: Hanne K J
authors.initials: HK
authors.lastname: Gonnissen
authors.affiliation: Department of Human Movement Sciences, School of Nutrition and Translational Research in Metabolism Maastricht University, Maastricht, The Netherlands.
authors.forename: Henrike M
authors.initials: HM
authors.lastname: Hamer
authors.affiliation: Department of Human Movement Sciences, School of Nutrition and Translational Research in Metabolism Maastricht University, Maastricht, The Netherlands.
authors.forename: Joan M G
authors.initials: JM
authors.lastname: Senden
authors.affiliation: Department of Human Movement Sciences, School of Nutrition and Translational Research in Metabolism Maastricht University, Maastricht, The Netherlands.
authors.forename: Luc J C
authors.initials: LJ
authors.lastname: van Loon
authors.affiliation: Department of Human Biology, School of Nutrition and Translational Research in Metabolism, Maastricht University, Maastricht, The Netherlands.
authors.forename: Margriet S
authors.initials: MS
authors.lastname: Westerterp-Plantenga
mesh_terms: D000328:Adult; D018753:Diet, Protein-Restricted; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000378:metabolism; D005215:Fasting / Q000097:blood; D005260:Female; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D010649:Phenylalanine / Q000097:blood; D014176:Protein Biosynthesis; D014443:Tyrosine / Q000097:blood; D055815:Young Adult
chemical_list: D004044:Dietary Proteins; D007328:Insulin; D009124:Muscle Proteins; D014443:Tyrosine; D010649:Phenylalanine; D005947:Glucose; D009584:Nitrogen