title: Increased protein maintains nitrogen balance during exercise-induced energy deficit.
abstract: OBJECTIVE
  This study examined how a high-protein diet affected nitrogen balance and protein turnover during an exercise-induced energy deficit.
  
  
  METHODS
  Twenty-two men completed a 4-d (D1-4) baseline period (BL) of an energy balance diet while maintaining usual physical activity level, followed by 7 d (D5-11) of 1000 kcal.d increased energy expenditure via exercise (50-65% V O2peak). One group consumed 0.9 g of protein per kilogram per day and maintained energy balance throughout the 11-d intervention (BAL, N = 8). The other two groups consumed their BL energy intake throughout the 11 days, resulting in a 7-d, 1000-kcal.d energy deficit. These groups consumed either 0.9 g of protein per kilogram per day (DEF, N = 7) or 1.8 g of protein per kilogram per day (DEF-HP, N = 7). Mean nitrogen balance (NB), calculated per kilogram of fat-free mass (FFM), was determined for BL, days 5-8 (EX1), and days 9-11 (EX2). Whole-body protein turnover was derived from phenylalanine and tyrosine kinetics assessed while fasting at rest on days 4, 7, and 12, using a priming dose of L-[ring-N]tyrosine and a 4-h, primed, continuous infusion of L-[N]phenylalanine and L-[ring-H4]tyrosine.
  
  
  RESULTS
  DEF experienced a decrease in NB from BL to EX 1 that was maintained in EX 2. No changes in NB occurred for BAL or DEF-HP over time. No within- or between-group differences were found over time for Phe flux (Qp), conversion rate of Phe to Tyr (Qpt), or the derived protein synthesis value (Sp).
  
  
  CONCLUSIONS
  Increased dietary protein maintained NB during exercise-induced energy deficit, but this did not impact resting whole-body protein turnover.
authors: U.S. Army Research Institute of Environmental Medicine, Natick, MA 01760, USA.
authors: Matthew A
authors: MA
authors: Pikosky
authors: Tracey J
authors: TJ
authors: Smith
authors: Ann
authors: A
authors: Grediagin
authors: Carmen
authors: C
authors: Castaneda-Sceppa
authors: Lauri
authors: L
authors: Byerley
authors: Ellen L
authors: EL
authors: Glickman
authors: Andrew J
authors: AJ
authors: Young
mesh_terms: D000328:Adult; D050528:Diet, Carbohydrate-Restricted; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D009584:Nitrogen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology
chemical_list: D004044:Dietary Proteins; D009584:Nitrogen