Background: The 1985 FAO/WHO/UNU upper requirement for the sulfur-containing amino acids in healthy adults, which was set at 13 mg . kg(-)(1) . d(-)(1), is based on nitrogen balance studies in Western subjects. Short-term tracer-based studies also estimated a mean requirement of 13 mg . kg(-)(1) . d(-)(1), but whether this estimate is applicable to healthy populations worldwide is unknown.
Objective: Using a 24-h indicator amino acid oxidation and balance method with 7 test methionine intakes (3, 6, 9, 13, 18, 21, and 24 mg . kg(-)(1) . d(-)(1)), we assessed methionine requirements in healthy, well-nourished Indians.
Design: Twenty-one healthy, well-nourished Indian men were studied during each of 3 randomly assigned 7-d diet periods in which methionine intakes (diet devoid of cysteine) were equally placed on either side of the putative mean methionine requirement of 13 mg . kg(-)(1) . d(-)(1). Twenty-four-hour indicator amino acid oxidation and balance were measured on day 7 by using a 24-h [(13)C]leucine tracer infusion. The breakpoint in the relation between these values and the methionine intake was determined.
Results: Two-phase linear regression of daily leucine oxidation against methionine intake estimated a breakpoint in the response curve at a methionine intake of 14 mg . kg(-)(1) . d(-)(1) (95% CI: 11, 23 mg . kg(-)(1) . d(-)(1)). The breakpoint estimated from the leucine balance-methionine intake relation was 15 mg . kg(-)(1) . d(-)(1) (95% CI: 11, 27 mg . kg(-1) . d(-1)).
Conclusions: From the 24-h indicator amino acid oxidation and balance approach, a mean methionine requirement, in the absence of cysteine intake, of 15 mg . kg(-1) . d(-1) is proposed for healthy, well-nourished Indian adults. This requirement is similar to that established in Western adults.