title: Threonine requirement of healthy adults, derived with a 24-h indicator amino acid balance technique.
abstract: BACKGROUND
  Because we question the validity of the 1985 FAO/ WHO/UNU upper requirement for threonine of 7 mg x kg(-1) x d(-1), we proposed a tentative mean requirement of 15 mg x kg(-1) x d(-1).
  
  
  OBJECTIVE
  Our goal was to assess threonine adequacy at 3 test intakes and the consequences of a 6-d compared with a 13-d dietary adaptation phase.
  
  
  METHODS
  We used a 24-h indicator amino acid balance technique ([1-(13)C]leucine as indicator) to assess the threonine requirement. Fifteen healthy adults were randomly assigned to receive 7, 15, or 46 mg threonine x kg(-1) x d(-1) and were studied after 6 and 13 d of adaptation to the experimental diets. Diets were based on an L-amino acid mixture in which the threonine content was varied. At 1700 on days 6 and 13, a 24-h intravenous [(13)C]leucine tracer infusion protocol was begun to assess leucine oxidation and daily leucine balances.
  
  
  RESULTS
  There was no detectable effect of duration of dietary adaptation in leucine oxidation or balance, but the 24-h leucine oxidation and balances differed significantly between the 7-mg intake and each of the 2 higher intakes (P < 0.05). The latter were not significantly different. The 24-h leucine oxidation rate decreased across threonine intakes (P < 0.01 for main effect of diet, independent of infusion day). Leucine oxidation was highly correlated (r = 0.80) between the 2 dietary adaptation phases across all test intakes.
  
  
  CONCLUSIONS
  The 1985 FAO/WHO/UNU threonine recommendation is inadequate, and 15 mg x kg(-1) x d(-1) is sufficient to achieve mean indicator (leucine) amino acid balance.
authors.affiliation: Laboratory of Human Nutrition, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Sudhir
authors.initials: S
authors.lastname: Borgonha
authors.forename: Meredith M
authors.initials: MM
authors.lastname: Regan
authors.forename: Seung-Ho
authors.initials: SH
authors.lastname: Oh
authors.forename: Mervelina
authors.initials: M
authors.lastname: Condon
authors.forename: Vernon R
authors.initials: VR
authors.lastname: Young
mesh_terms: D000328:Adult; D004032:Diet; D005260:Female; D006801:Humans; D007930:Leucine / Q000097:blood / Q000378:metabolism; D008297:Male; D009751:Nutritional Requirements; D011849:Radioactive Tracers; D013912:Threonine / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*
chemical_list: D011849:Radioactive Tracers; D013912:Threonine; D007930:Leucine