How can carbohydrate metabolism be measured during exercise?
ππππππ΄ββοΈπ΄ββοΈβΉοΈβΉοΈββοΈ
New #openaccess review by @AndyJKing & I in @IJSNEMJournal
Hopefully a useful resource for people researching & reading about exercise metabolism π©βπ¬π
A summaryπ§΅1/12
doi.org/10.1123/ijsnemβ¦
ππππππ΄ββοΈπ΄ββοΈβΉοΈβΉοΈββοΈ
New #openaccess review by @AndyJKing & I in @IJSNEMJournal
Hopefully a useful resource for people researching & reading about exercise metabolism π©βπ¬π
A summaryπ§΅1/12
doi.org/10.1123/ijsnemβ¦
What are isotope tracers?
Molecules where certain elements (e.g. Carbon) differ in some ways (mass) but less so in others (function)
This means we can distinguish between "label" and naturally occurring molecules, whilst the label behaves similarly to the natural molecule
2/12
Molecules where certain elements (e.g. Carbon) differ in some ways (mass) but less so in others (function)
This means we can distinguish between "label" and naturally occurring molecules, whilst the label behaves similarly to the natural molecule
2/12
Molecules (e.g. glucose) can be labelled in different ways.
e.g. just one carbon could be labelled (13C) in a specific position
or all the carbons could be labelled (13C), known as uniformly or universally labelled (U-13C)
3/12
e.g. just one carbon could be labelled (13C) in a specific position
or all the carbons could be labelled (13C), known as uniformly or universally labelled (U-13C)
3/12
Tracers are important because they can reveal underlying flux
This cannot be discerned from concentrations alone
With exercise vs rest, plasma glucose concentrations may not change, but flux (diss/appearance) can be higher
(2-fold β¬οΈ in this e.g.doi.org/10.1152/ajpendβ¦)
4/12
This cannot be discerned from concentrations alone
With exercise vs rest, plasma glucose concentrations may not change, but flux (diss/appearance) can be higher
(2-fold β¬οΈ in this e.g.doi.org/10.1152/ajpendβ¦)
4/12
To measure rates of appearance (Ra) & disappearance (Rd), we need to infuse a known about of tracer into a vein.
Then measure changes in concentration and tracer enrichment over time.
The relationship between these two can tell us a lot (based on the dilution principle).
5/12
Then measure changes in concentration and tracer enrichment over time.
The relationship between these two can tell us a lot (based on the dilution principle).
5/12
There are potential issues during non-steady-state (e.g. rest-to-exercise or fasted-to-fed transition)
Due to the time taken to equilibrate between different pools (for glucose, plasma & interstitial fluid)
Meaning what we measure might not reflect what we think is it
6/12
Due to the time taken to equilibrate between different pools (for glucose, plasma & interstitial fluid)
Meaning what we measure might not reflect what we think is it
6/12
This needs to be considered in study design, and can be somewhat overcome by using specific equations
7/12
7/12
If we combine the infusion of tracer with ingestion of tracer, we can understand what happens to endogenous and exogenous (ingested) carbohydrates
E.g. do we burn the carbohydrate or store it?
8/12
E.g. do we burn the carbohydrate or store it?
8/12
This has been used in many studies during exercise to assess how much of sports drinks/gels are used as fuel during the exercise
doi.org/10.1152/japplpβ¦
9/12
doi.org/10.1152/japplpβ¦
9/12
There are some considerations when using these methods including
Limiting foods naturally high in some isotopes (13C) to increase signal-to-noise ratio
Maintaining steady-state before measures
10/12
Limiting foods naturally high in some isotopes (13C) to increase signal-to-noise ratio
Maintaining steady-state before measures
10/12
Check out the paper for more detail on these methods and things to consider
doi.org/10.1123/ijsnemβ¦
11/12
doi.org/10.1123/ijsnemβ¦
11/12
Finally, thanks @LouiseMBurke @MckayAlannah & @DrBSteamjets for the invitation to write this review, and to collaborators on tracers @gareth_wallis @Hodson_Group
Dedicated to @proftipper who encouraged me to apply for my first grant using tracers and supported the setup
12/12
Dedicated to @proftipper who encouraged me to apply for my first grant using tracers and supported the setup
12/12
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