In the past decade, we've gone from low carb to high carb. Are we now heading towards a new era of personalised carb? In this episode I speak to two experts about exactly what exogenous carbohydrate oxidation is, how the testing works, who might benefit from this type of testing, and how to interpret the results.
Timestamps:
04:09 - Tim and Gareth's background and research
10:50 - What is exogenous carbohydrate oxidation?
11:41 - How do you test exogenous carbohydrate oxidation rate?
16:26 - How should an athlete prepare for exogenous oxidation testing?
19:10 - The importance of doing the test properly
22:50 - Are we testing maximal oxidation capacity, or replicating race conditions?
23:44 - What's the real-world benefit of exogenous carbohydrate oxidation testing?
28:17 - Making this testing available to athletes
33:58 - Assumptions, caveats and limitations to exogenous oxidation testing
37:33 - The difference between relative and absolute exercise intensity - does it matter here?
40:52 - What happens when you overfeed carbohydrate during exercise
43:59 - Why Tim and Gareth only test for glucose (and not fructose) oxidation
47:13 - How carb intake recommendations are made based on test results
50:58 - Can you improve exogenous oxidation through exercise or gut training?
57:26 - The (very) high carb trend - will testing help prevent unnecessary carb intake?
1:00:48 - Who might benefit most from testing, and do gut issues predict oxidation abiilty?
1:07:35 - Unanswered questions in this area
1:10:37 - Bonus Round
1:13:42 - Summary, unanswered questions and wrap up
Research mentioned in this episode:
Podlogar T, Cooper-Smith N, Gonzalez JT, Wallis GA. (2025). Personalised carbohydrate feeding during exercise based on exogenous glucose oxidation: a proof-of-concept study. Performance Nutrition. 1:2. doi: 10.1186/s44410-025-00003-9
Dr Tim Podlogar:
University of Exeter: experts.exeter.ac.uk/43996-tim-podlogar
Instagram: @tpodlogar
LinkedIn: linkedin.com/in/timpodlogar
Prof Gareth Wallis:
University of Birmingham: birmingham.ac.uk/staff/profiles/sportex/wallis-gareth
LinkedIn: linkedin.com/in/gareth-wallis-8291a441/
Oxidation testing service (Fuel Sync) coming in Jan 2026
Fueling Endurance eBook | T -12 Race Nutrition Course | Practitioner Resources
The Fueling Endurance eBook contains answers to 49 of the most common nutrition questions that runners, cyclists and triathletes ask, and contains insights, tips, and quotes from experts and athletes. The T -12 self-guided course will help prepare you for your next event, with online tools, guides, information and instructions to take you through the 12 weeks leading up to race day. And the Fueling Endurance Practitioner Membership provides access to online tools and calculators I use all the time when working with endurance and ultraendurance athletes. This includes working out the carbohydrate needs for runners (road and trail) and cyclists for different types of training sessions. For more into on each of these, check out fuelingendurance.com.
