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Annual Meeting Abstracts: E-21 – Free Communication/Slide: Protein and Exercise

Estrogen Supplementation Reduces Leucine Oxidation at Rest and During Moderate Intensity Endurance Exercise in Men

Hamadeh, Mazen J.; Devries, Michaela C.; Tarnopolsky, Mark A.

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Medicine & Science in Sports & Exercise: May 2004 - Volume 36 - Issue 5 - p S194
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Healthy active men exhibit higher rates of leucine oxidation as compared with their female counterparts both at rest and during moderate intensity endurance exercise. We postulated that this reduced dependence on amino acids as a fuel source in women was due to the female sex hormone estrogen (ES). PURPOSE: To investigate the effect of supplementing recreationally active men with ES on leucine oxidation at rest and during moderate intensity endurance exercise. METHODS: In a randomized, doubleblind, cross-over design, we measured leucine oxidation in eleven men after eight days of either ES supplementation (2 mg 17β-estradiol/day) or placebo (PL, polycose) prior to and during 90 min of cycling at an intensity of 65% VO2max. Following a two-week washout period, they repeated the test after eight days on the alternate treatment. On the test day, following a primed continuous infusion of L-[13C]leucine, VCO2 and steady state breath 13CO2 and plasma [13C]α-KIC enrichments were measured at rest and 60, 75 and 90 min during exercise in the postabsorptive state. RESULTS: ES supplementation significantly decreased leucine oxidation, whereas exercise increased it 2.3 fold (see table). CONCLUSION: We conclude that estrogen influences fuel source selection at rest and during endurance exercise in recreationally active men characterized by a reduced dependence on amino acids as a fuel source. (This research was funded by Hamilton Health Sciences Corporation, NSERC and National Institute of Nutrition).

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Data are leucine oxidation in μmol/kg/h (mean ± SEM, n = 11). Two-way repeated measures ANOVA; * main effect of estrogen, P = 0.019; † main effect of exercise, P < 0.0001.

©2004The American College of Sports Medicine