Lysine requirement of adult males is not affected by decreasing dietary protein.
Recently, we reported the lysine requirement to be 41.2 mg.kg-1.d-1 using indicator amino acid oxidation (IAAO) in healthy adult males fed a protein intake of 1.0 g.kg-1.d-1. A lower protein intake has been hypothesized to significantly lower the requirement estimate. We tested this hypothesis using IAAO by estimating the lysine requirement at a protein intake of 0.8 g.kg-1.d-1 in five healthy adult males. Lysine requirement was determined from the rate of appearance of 13CO2 in breath (F13CO2) by using a primed 4-h continuous infusion of L-[1-(13)C]phenylalanine. Phenylalanine flux was not affected by graded increases in dietary lysine. Phenylalanine oxidation and F13CO2 decreased linearly (P < 0.05) as lysine intake increased to a breakpoint, after which the rates were not significantly different. Two-phase linear regression determined this breakpoint (mean lysine requirement) to occur at a dietary lysine intake of 45.0 mg.kg-1.d-1. We conclude that no reduction appears in the lysine requirement with a lower protein intake. Thus, lysine requirement appears not to be altered by protein intakes within the lower end of the protein requirement range.
Department of Nutritional Sciences, University of Toronto, Ontario, Canada.
A M
AM
Duncan
R O
RO
Ball
P B
PB
Pencharz
D000328:Adult; D000596:Amino Acids / Q000378:metabolism; D001823:Body Composition / Q000502:physiology; D015992:Body Mass Index; D002245:Carbon Dioxide / Q000378:metabolism; D004044:Dietary Proteins / Q000032:analysis / Q000494:pharmacology* / Q000592:standards; D002149:Energy Intake / Q000502:physiology; D006801:Humans; D016014:Linear Models; D008239:Lysine / Q000032:analysis / Q000494:pharmacology* / Q000592:standards; D008297:Male; D009751:Nutritional Requirements; D010084:Oxidation-Reduction; D010649:Phenylalanine / Q000378:metabolism; D013997:Time Factors
D000596:Amino Acids; D004044:Dietary Proteins; D002245:Carbon Dioxide; D010649:Phenylalanine; D008239:Lysine