Leucine-enriched protein feeding does not impair exercise-induced free fatty acid availability and lipid oxidation: beneficial implications for training in carbohydrate-restricted states
Open accessAbstract
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.
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Consuming approximately 20 g of whey protein before and during CHO-restricted training sessions still permits mobilization of free fatty acids.
“Indeed, consuming approximately 20 g of whey protein before and during CHO-restricted training sessions still permits mobilization of FFAs [33] and activation of the AMPK signalling axis [34], while also improving net muscle protein balance [35].”
From Fuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis (2018) · cites this paper as [33]
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Impey, S. G., Hearris, M. A., Hammond, K. M., Bartlett, J. D., Louis, J., Close, G. L., & Morton, J. P. (2018) · Sports Medicine · doi:10.1007/s40279-018-0867-7 · Cited by 232 · see citing works
“Indeed, consuming approximately 20 g of whey protein before and during CHO-restricted training sessions still permits mobilization of FFAs [33] and activation of the AMPK signalling axis [34], while also improving net muscle protein balance [35].”
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- Authors
- Impey, S. G., Smith, D., Robinson, A. L., Owens, D. J., Bartlett, J. D., Smith, K., Limb, M., Tang, J., Fraser, W. D., Close, G. L., & Morton, J. P.
- Affiliations
- Liverpool John Moores University (GB)
- University of Nottingham (GB)
- University of East Anglia (GB)
- Corresponding author
- Morton, James P.
- ORCID
- Venue
- Amino Acids
- Published
- 2014-12-04
- Volume
- 47
- Issue
- 2
- Pages
- 407-416
- ISSN
- 0939-4451 (ISSN-L)
- 1438-2199
- OpenAlex
- W2026850130
- Cited by
- 34
- References
- 46
- Citations by year
- 2026: 1 · 2025: 2 · 2024: 3 · 2023: 3 · 2022: 2 · 2021: 3 · 2020: 7 · 2019: 3 · 2018: 4 · 2017: 2 · 2016: 4
- FWCI
- 1.00
- Type
- journal article
- Language
- en
- Open access
- Licence
- www.springer.com/tdm (tdm)
- Locations
- Amino Acids (publishedVersion)
- PubMed (publishedVersion)
- Liverpool John Moores University (submittedVersion)
- UEA Digital Repository (University of East Anglia) (submittedVersion)
- Victoria University Research Repository (Victoria University) (submittedVersion)
- Topics
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Muscle metabolism and nutrition
- Health Sciences › Medicine › Complementary and alternative medicine › Cardiovascular and exercise physiology
- Health Sciences › Medicine › Physiology › Diet and metabolism studies
- Keywords
- whey protein, physical activity, carbohydrate restriction, fasting, plasma leucine, insulin, skeletal muscle adaptation, endurance training, muscle protein synthesis
- MeSH terms
- Adult, Dietary Proteins, Fatty Acids, Nonesterified, Humans, Leucine, Male, Exercise, Lipid Metabolism, Diet, Carbohydrate-Restricted
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