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Protein Requirements Are Elevated in Endurance Athletes after Exercise as Determined by the Indicator Amino Acid Oxidation Method

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Kato, Hiroyuki, Suzuki, Katsuya, Bannai, Makoto, Moore, Daniel R.·2016·PLOS ONE
DOI 10.1371/journal.pone.0157406PMC PMC4913918
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Abstract

UNLABELLED: A higher protein intake has been recommended for endurance athletes compared with healthy non-exercising individuals based primarily on nitrogen balance methodology. The aim of this study was to determine the estimated average protein requirement and recommended protein intake in endurance athletes during an acute 3-d controlled training period using the indicator amino acid oxidation method. After 2-d of controlled diet (1.4 g protein/kg/d) and training (10 and 5km/d, respectively), six male endurance-trained adults (28±4 y of age; Body weight, 64.5±10.0 kg; VO2peak, 60.3±6.7 ml·kg-1·min-1; means±SD) performed an acute bout of endurance exercise (20 km treadmill run) prior to consuming test diets providing variable amounts of protein (0.2-2.8 g·kg-1·d-1) and sufficient energy. Protein was provided as a crystalline amino acid mixture based on the composition of egg protein with [1-13C]phenylalanine provided to determine whole body phenylalanine flux, 13CO2 excretion, and phenylalanine oxidation. The estimated average protein requirement was determined as the breakpoint after biphasic linear regression analysis with a recommended protein intake defined as the upper 95% confidence interval. Phenylalanine flux (68.8±8.5 μmol·kg-1·h-1) was not affected by protein intake. 13CO2 excretion displayed a robust bi-phase linear relationship (R2 = 0.86) that resulted in an estimated average requirement and a recommended protein intake of 1.65 and 1.83 g protein·kg-1·d-1, respectively, which was similar to values based on phenylalanine oxidation (1.53 and 1.70 g·kg-1·d-1, respectively). We report a recommended protein intake that is greater than the RDA (0.8 g·kg-1·d-1) and current recommendations for endurance athletes (1.2-1.4 g·kg-1·d-1). Our results suggest that the metabolic demand for protein in endurance-trained adults on a higher volume training day is greater than their sedentary peers and current recommendations for athletes based primarily on nitrogen balance methodology. TRIAL REGISTRATION: ClinicalTrial.gov NCT02478801.

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  • Endurance athletes are recommended to consume ~1.2-1.8 g·kg-1 of high-quality protein.

    “Endurance athletes are recommended to consume ~ 1.2–1.8 g·kg–1 of high-quality protein [69–72]”

    From Nutritional Strategies to Improve Post-exercise Recovery and Subsequent Exercise Performance: A Narrative Review (2025) · cites this paper as [70]

    The Discussion reports earlier recommendations of 1.2–1.4 g/kg/day for endurance athletes and this study’s recommended intake of 1.83 g/kg/day, supporting the approximate endpoints. It does not recommend a single 1.2–1.8 g/kg/day range of high-quality protein; the 1.83 estimate comes from a specific controlled-training and post-exercise setting. No page numbers are available in our copy. (LLM, conf=0.85)

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  • The contribution from protein is not negligible, as evidenced by profound alterations in whole body protein metabolism and amino acid kinetics in response to exercise that consequently regulate fuel metabolism and the adaptive response to training.

    “but by no means is the contribution from protein negligible, as evidenced by the profound alterations in whole body protein metabolism and amino acid kinetics in response to exercise that consequently regulate fuel metabolism and the adaptive response to training [166,168,169,170].”

    From Regulation of Energy Substrate Metabolism in Endurance Exercise (2021) · cites this paper as [170]

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  • Depending on training volume, dietary recommendations for endurance athletes range from approximately 1.2 to 1.6 g/kg body mass per day to support recovery, promote training adaptations, and account for the contribution of elevated amino acid oxidation rates during exercise.

    “Depending on training volume, dietary recommendations for endurance athletes range from ∼1.2 to 1.6 g/kg BM/d to support recovery, promote training adaptations, and account for the contribution of elevated amino acid oxidation rates during exercise [55,[57], [58], [59]].”

    From Nutritional Considerations for the Vegan Athlete (2023) · cites this paper as [57]

  • Based on nitrogen-balance methodology, protein intakes of >1.6 g·kg−1·d−1 have been recommended for endurance athletes who have high training demands.

    “Based on nitrogen-balance methodology, protein intakes of > 1.6 g·kg− 1·d− 1 have been recommended for endurance athletes who have high training demands [35].”

    From International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing (2019) · cites this paper as [35]

  • Current evidence indicates that protein intakes of less than 1.6 g·kg−1·d−1 may result in a negative nitrogen balance in endurance athletes who have high training demands.

    “Current evidence indicates that protein intakes of less than 1.6 g·kg− 1·d− 1 may result in a negative nitrogen balance in endurance athletes who have high training demands [35].”

    From International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing (2019) · cites this paper as [35]

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Authors
Kato, H., Suzuki, K., Bannai, M., & Moore, D. R.
Affiliations
  • University of Toronto (CA)
  • Ajinomoto (Japan) (JP)
Corresponding author
Moore, Daniel R.
ORCID
Venue
PLOS ONE
Publisher
Public Library of Science (PLoS)
Published
2016-06-20
Volume
11
Issue
6
Pages
e0157406
ISSN
1932-6203 (ISSN-L)
DOI
10.1371/journal.pone.0157406
PMC
PMC4913918
OpenAlex
W2461348852
Cited by
128
References
60
Citations by year
2026: 4 · 2025: 14 · 2024: 8 · 2023: 17 · 2022: 8 · 2021: 16 · 2020: 17 · 2019: 20 · 2018: 18 · 2017: 6
FWCI
10.08
Type
journal article
Language
en
Open access
Licence
Locations
  • PLoS ONE (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
  • Figshare (submittedVersion, cc-by)
Funders
Ajinomoto Inc. Co.
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Muscle metabolism and nutrition
  • Health Sciences › Medicine › Orthopedics and Sports Medicine › Sports Performance and Training
  • Health Sciences › Medicine › Complementary and alternative medicine › Cardiovascular and exercise physiology
Keywords
protein requirements, endurance athletes, protein intake, indicator amino acid oxidation, phenylalanine oxidation, 13CO2 excretion, acute endurance exercise, nitrogen balance, RDA, amino acid metabolism
MeSH terms
Adult, Body Weight, Energy Intake, Dietary Proteins, Female, Humans, Male, Nutritional Requirements, Oxidation-Reduction, Phenylalanine, Physical Endurance, Exercise, Athletes

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