Threonine requirements of healthy Indian men, measured by a 24-h indicator amino acid oxidation and balance technique.
BACKGROUND
We previously questioned the validity of the 1985 FAO/WHO/UNU upper requirement value for threonine (7 mg x kg(-1) x d(-1)) and proposed a tentative mean requirement of 15 mg x kg(-1) x d(-1).


OBJECTIVE
In this study we used a 24-h indicator amino acid oxidation and balance technique, with [1-(13)C]leucine as the indicator amino acid, to assess threonine adequacy at 6 test intakes (7, 11, 15, 19, 22, and 27 mg x kg(-1) x d(-1)) with a 6-d dietary adaptation phase in healthy, well-nourished Indian men.


METHODS
Sixteen men were randomly allocated to 3 of 6 test intakes and were studied after 6 d of adaptation to the experimental diets. Diets were based on an L-amino acid mixture in which the threonine content was varied. At 1800 on day 6, a 24-h intravenous [(13)C]leucine tracer infusion protocol was conducted to assess 24-h leucine oxidation and daily leucine balances.


RESULTS
Leucine balances differed significantly (P = 0.02) between the different intakes of threonine. Two-phase linear regression analysis from 12-h and 24-h leucine oxidation and 24-h leucine balance gave a breakpoint at a threonine intake of 15 mg x kg(-1) x d(-1), with 95% CIs ranging from 11 to 27 mg x kg(-1) x d(-1). There was no significant effect of threonine intake on 24-h leucine flux.


CONCLUSIONS
The results of the 24-h indicator amino acid oxidation and balance experiments indicate that the current FAO/WHO/UNU threonine recommendation of 7 mg x kg(-1) x d(-1) is inadequate. A mean threonine intake of 15 mg x kg(-1) x d(-1) is sufficient to achieve the indicator (leucine) amino acid balance in healthy Indian men.
D000293:Adolescent; D000328:Adult; D000596:Amino Acids / Q000097:blood / Q000378:metabolism*; D002153:Calorimetry, Indirect; D002247:Carbon Isotopes; D004032:Diet; D002149:Energy Intake; D005215:Fasting; D006801:Humans; D007194:India; D007202:Indicators and Reagents; D007700:Kinetics; D007930:Leucine / Q000097:blood / Q000378:metabolism; D016014:Linear Models; D008297:Male; D018673:Nutrition Policy; D009751:Nutritional Requirements; D010084:Oxidation-Reduction; D012885:Skinfold Thickness; D013912:Threonine / Q000008:administration & dosage* / Q000097:blood
D000596:Amino Acids; D002247:Carbon Isotopes; D007202:Indicators and Reagents; D013912:Threonine; D007930:Leucine