title: Leucine-enriched protein feeding does not impair exercise-induced free fatty acid availability and lipid oxidation: beneficial implications for training in carbohydrate-restricted states.
abstract: Given that the enhanced oxidative adaptations observed when training in carbohydrate (CHO)-restricted states is potentially regulated through free fatty acid (FFA)-mediated signalling and that leucine-rich protein elevates muscle protein synthesis, the present study aimed to test the hypothesis that leucine-enriched protein feeding enhances circulating leucine concentration but does not impair FFA availability or whole body lipid oxidation during exercise. Nine males cycled for 2 h at 70% VO2peak when fasted (PLACEBO) or having consumed a whey protein solution (WHEY) or a leucine-enriched whey protein gel (GEL), administered as 22 g 1 h pre-exercise, 11 g/h during and 22 g 30 min post-exercise. Total leucine administration was 14.4 g and 6.3 in GEL and WHEY, respectively. Mean plasma leucine concentrations were elevated in GEL (P = 0.001) compared with WHEY and PLACEBO (375 ± 100, 272 ± 51, 146 ± 14 µmol L(-1), respectively). No differences (P = 0.153) in plasma FFA (WHEY 0.53 ± 0.30, GEL 0.45 ± 0.25, PLACEBO 0.65 ± 0.30, mmol L(-1)) or whole body lipid oxidation during exercise (WHEY 0.37 ± 0.26, GEL 0.36 ± 0.24, PLACEBO 0.34 ± 0.24 g/min) were apparent between trials, despite elevated (P = 0.001) insulin in WHEY and GEL compared with PLACEBO (38 ± 16, 35 ± 16, 22 ± 11 pmol L(-1), respectively). We conclude that leucine-enriched protein feeding does not impair FFA availability or whole body lipid oxidation during exercise, thus having practical applications for athletes who deliberately train in CHO-restricted states to promote skeletal muscle adaptations.
authors.affiliation: Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Tom Reilly Building, Byrom St Campus, Liverpool, L3 3AF, UK.
authors.forename: Samuel G
authors.initials: SG
authors.lastname: Impey
authors.forename: Dominic
authors.initials: D
authors.lastname: Smith
authors.forename: Amy L
authors.initials: AL
authors.lastname: Robinson
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Owens
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Bartlett
authors.forename: Kenneth
authors.initials: K
authors.lastname: Smith
authors.forename: Marie
authors.initials: M
authors.lastname: Limb
authors.forename: Jonathan
authors.initials: J
authors.lastname: Tang
authors.forename: William D
authors.initials: WD
authors.lastname: Fraser
authors.forename: Graeme L
authors.initials: GL
authors.lastname: Close
authors.forename: James P
authors.initials: JP
authors.lastname: Morton
mesh_terms: D000328:Adult; D050528:Diet, Carbohydrate-Restricted; D004044:Dietary Proteins / Q000008:administration & dosage*; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood*; D006801:Humans; D007930:Leucine / Q000008:administration & dosage* / Q000097:blood*; D050356:Lipid Metabolism / Q000502:physiology*; D008297:Male
chemical_list: D004044:Dietary Proteins; D005230:Fatty Acids, Nonesterified; D007930:Leucine