title: Efficiency of utilization of wheat and milk protein in healthy adults and apparent lysine requirements determined by a single-meal [1-13C]leucine balance protocol.
abstract: BACKGROUND
  We recently reported better wheat-protein utilization and a higher apparent lysine requirement than would be predicted, because of adaptive mechanisms of lysine conservation. However, such findings may be subject to the feeding protocol of frequent small meals.
  
  
  OBJECTIVE
  We used a [1-13C]leucine balance, large single-meal protocol to estimate the utilization of wheat and the consequent lysine requirements.
  
  
  METHODS
  Wheat and milk utilization were compared in 5 adults infused for 9 h with L-[1-13C]leucine, in the postabsorptive (0-3 h) and postprandial (3-9 h) states after ingestion of a single meal of either milk (30.4 kJ/kg; 32% of energy as protein) or a mixture of wheat gluten and whole wheat (29.2 kJ; 26.7% of energy as protein). Premeal nitrogen balance was predicted from [1-13C]leucine oxidation and postmeal balance predicted from cumulative increased leucine oxidation, enabling evaluation of the metabolic demand for protein, the efficiency of postprandial protein utilization (PPU), and the requirements for wheat protein and lysine.
  
  
  RESULTS
  Mean (+/-SD) PPU was 0.61 +/- 0.03 and 0.93 +/- 0.02 for wheat and milk (P < or = 0.001), respectively, and the estimated average wheat-protein requirement (0.6 g.kg(-1).d(-1)/PPU) was 0.98 +/- 0.05 g.kg(-1).d(-1), indicating a lysine requirement of 18.3 +/- 1.0 mg. kg(-1).d(-1).
  
  
  CONCLUSIONS
  Measured wheat utilization efficiency at 0.61 was considerably higher than the value predicted from wheat lysine intake and milk protein lysine deposition (ie, 0.222 +/- 0.004). These results confirm our previous finding that lysine conservation allows wheat protein to be utilized more efficiently than expected and is consistent with a lysine requirement in fully adapted individuals of 19 mg.kg(-1).d(-1), as indicated by recalculated nitrogen balance data.
authors.affiliation: Centre for Nutrition and Food Safety, School of Biomedical and Health Sciences, University of Surrey, Guildford, United Kingdom. d.millward@surrey.ac.uk
authors.forename: D Joe
authors.initials: DJ
authors.lastname: Millward
authors.forename: Amelia
authors.initials: A
authors.lastname: Fereday
authors.forename: Neil R
authors.initials: NR
authors.lastname: Gibson
authors.forename: Malcolm C
authors.initials: MC
authors.lastname: Cox
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Pacy
mesh_terms: D000328:Adult; D002247:Carbon Isotopes; D004044:Dietary Proteins / Q000493:pharmacokinetics; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood; D007700:Kinetics; D007930:Leucine / Q000008:administration & dosage* / Q000097:blood; D008239:Lysine / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D008894:Milk Proteins / Q000493:pharmacokinetics*; D009584:Nitrogen / Q000008:administration & dosage; D009751:Nutritional Requirements; D010084:Oxidation-Reduction; D010940:Plant Proteins / Q000493:pharmacokinetics*; D014908:Triticum / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes; D004044:Dietary Proteins; D007328:Insulin; D008894:Milk Proteins; D010940:Plant Proteins; D007930:Leucine; D008239:Lysine; D009584:Nitrogen