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Determination of the Tolerable Upper Limit (UL) of Leucine Intake in Adult Humans
Author(s) -
Elango Rajavel,
Chapman Karen,
Rafii Mahroukh,
Ball Ronald O,
Pencharz Paul B
Publication year - 2010
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.24.1_supplement.lb274
Subject(s) - leucine , chemistry , amino acid , food science , zoology , medicine , biochemistry , biology
The branched‐chain amino acids (BCAA) include leucine and are popular as dietary supplements among strength training athletes. Leucine has been implicated to improve athletic performance, although experimental evidence is inconclusive, and raises concerns regarding adverse effects. Our objective was to determine the ‘metabolic limit’ to oxidize leucine in vivo . Four, healthy adults (20‐35 y) each received graded stepwise increases in leucine intakes of 50, 150, 250, 500, 750, 1000 and 1250 mg/kg/d corresponding to the Estimated Average Requirement (EAR), EARx3, x5, x10, x15, x20 and x25 to a total of 25 studies. The safe upper limit (UL) of leucine intake was determined by measuring the oxidation of L‐[1‐ 13 C]‐Leucine to 13 CO 2 ( F 13 CO 2 ). Breath samples were collected at baseline and isotopic steady state. Linear regression crossover analysis identified a breakpoint (UL) in F 13 CO 2 . The mean upper metabolic limit to oxidize leucine was determined to be 555.8 mg/kg/d ( Figure 1). These results correspond to 10 X the EAR for leucine. This study is the first to directly estimate the safe upper limit of leucine intake in humans and raises concerns that intakes greater than 555 mg/kg/d may be a risk to health because this is the upper limit of oxidative capacity in humans. (Supported by ICAAS). 1Leucine oxidation ( F 13 CO 2 , μmol/kg/hr) in response to graded excess leucine intakes