Twenty-four-hour oral tracer studies with L-[1-C-13]lysine at a low (15 mgcenter dot kg(-1)center dot d(-1)) and intermediate (29 mg-kg(-1)center dot d(-1)) lysine intake in healthy adults

Background: We proposed previously that the mean lysine requirement value i s approximate to 30 mg.kg(-1).d(-1) rather than the proposed 1985 FAO/WHO/U NU estimate of the upper range of the requirement, which is 12 mg.kg(-1).d( -1). Objective: Our objective was to explore the 24-h pattern and rate of whole- body lysine [1-C-13]oxidation and status of whole-body lysine balance in he althy, young adults given an L-aminoacid diet supplying either a low lysine intake (14-15 mg.kg(-1).d(-1)) or an intermediate lysine intake (29 mg.kg( -1).d(-1)) for 6 d before a continuous tracer study with L-[1-C-13]lysine. Design: Five subjects received the low lysine intake, 6 subjects received t he intermediate intake, and all were studied by using a standard 24-h oral tracer protocol that was described earlier for studies at a generous Lysine intake. Results: The rate of lysine oxidation was not significantly different betwe en the 12-h fasted and 12-h fed states, The daily oxidation rate ((x) over bar +/- SD) was 27.9 +/- 8.8 acid 27.3 +/- 17.6 mg lysine.kg(-1).d(-1) for the low- and intermediate-intake groups, respectively (NS). Daily lysine ba lance was -12.4 +/- 92 and 1.8 +/- 17.7 mg.kg(-1).d(-1), respectively (P < 0.025), for the low and intermediate intakes. The balance was significantly less than zero (P < 0.001) for the low intake. Conclusion: The FAO/WHO/UNU lysine requirement value is not sufficient to m aintain lysine homeostasis in healthy adults. From the results of this and tracer studies done by others, the mean lysine requirement of healthy adult s was determined to be 30 mg.kg(-1).d(-1).