Cited by 2,365Muscle metabolism and nutritionClinical Nutrition and GastroenterologyBody Composition Measurement Techniques

Calculation of substrate oxidation rates in vivo from gaseous exchange.

Frayn, K. N.·1983·Journal of Applied Physiology

Abstract

This paper reviews the assumptions involved in calculating rates of carbohydrate and fat oxidation from measurements of O2 consumption, CO2 production, and urinary nitrogen excretion. It is shown that erroneous results are obtained in the presence of metabolic processes such as lipogenesis and gluconeogenesis. The apparent rates calculated under these conditions can, however, be interpreted as net rates of "utilization." Thus the apparent rate of carbohydrate oxidation is the sum of the rates of utilization for oxidation and for lipogenesis minus the rate at which carbohydrate is formed from amino acids. The apparent rate of fat oxidation is the difference between the rates of oxidation and synthesis from carbohydrate, so that the apparently negative rates encountered in patients infused with glucose do quantitatively represent net rates of synthesis. Other processes such as synthesis of ketone bodies or lactate at rates greater than their utilization can also disturb the calculations, but the magnitude of the effect can be estimated from appropriate measurements. Methods of correcting the observed gaseous exchange in these circumstances are given.

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Crossref · 10.1152/jappl.1983.55.2.628

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Authors
Frayn, K. N.
Corresponding author
Frayn, K. N.
Venue
Journal of Applied Physiology
Published
1983-08-01
Volume
55
Issue
2
Pages
628-634
ISSN
  • 0161-7567 (ISSN-L)
  • 8750-7587
  • 1522-1601
OpenAlex
W2131501155
Cited by
2,365
References
15
Citations by year
2026: 66 · 2025: 85 · 2024: 89 · 2023: 96 · 2022: 103 · 2021: 94 · 2020: 130 · 2019: 99 · 2018: 97 · 2017: 96 · 2016: 90 · 2015: 82 · 2014: 72 · 2013: 68 · 2012: 72
FWCI
1.41
Type
journal article
Language
en
Open access
closed
Locations
  • Journal of Applied Physiology (publishedVersion)
  • PubMed (publishedVersion)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Muscle metabolism and nutrition
  • Health Sciences › Nursing › Nutrition and Dietetics › Clinical Nutrition and Gastroenterology
  • Health Sciences › Medicine › Physiology › Body Composition Measurement Techniques
Keywords
carbohydrate oxidation, fat oxidation, oxygen consumption, CO2 production, urinary nitrogen excretion, lipogenesis, gluconeogenesis, ketone body synthesis, lactic acid production, glucose infusion, in vivo metabolism
MeSH terms
Gluconeogenesis, Glucose, Humans, Lipids, Mathematics, Oxidation-Reduction, Pulmonary Gas Exchange

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