Background: In earlier studies with well-nourished subjects that used a 24-h indicator amino acid oxidation or balance approach, we concluded that the 1985 FAO/WHO/UNU requirement for lysine (12 mg x kg(-1) x d(-1)) was inadequate for healthy South Asian subjects and proposed a tentative requirement of 30 mg x kg(-1) x d(-1).
Objective: We assessed whether chronic undernutrition, with low habitual dietary protein and lysine intakes, leads to changed lysine requirements.
Design: Twenty-seven otherwise clinically healthy, chronically undernourished Indian men were studied during 2 randomly assigned 7-d diet periods supplying 12 and 30, 18 and 36, or 24 and 42 mg lysine x kg(-1) x d(-1), based on an L-amino acid diet. The subjects' leucine intake was 40 mg x kg(-1) x d(-1). At 1800 on day 6, a 24-h intravenous [(13)C]leucine tracer-infusion protocol was conducted to assess leucine oxidation and daily leucine balance at each test lysine intake.
Results: A breakpoint was not identified in the lysine intake-leucine oxidation or balance response over the range of intakes studied. Mixed-models linear regression analysis indicated a mean requirement of 44 mg lysine x kg(-1) x d(-1) (95% CI: 36, 63) for the lysine intake-leucine balance relation.
Conclusions: The mean lysine requirement in chronically undernourished men is estimated to be higher than the value of 30 mg x kg(-1) x d(-1) proposed for well-nourished individuals. This may be related to body-composition differences. It also suggests that these subjects have not elicited a metabolic adaptation in response to their habitually low lysine intakes by substantially improving their efficiency of dietary lysine utilization.