Carbohydrate Per Hour in Ultra Running: 90 vs 120 Grams with Paul Booth
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Episode Summary
Paul Booth, sports nutritionist, exercise physiologist and PhD researcher in ultra-running metabolism, is back on Mikkipedia, straight from UTMB week in Chamonix, where he raced OCC and worked with elite athletes. Mikki and Paul pick up where they left off a year ago, talking about how much carbohydrate trail and ultra runners actually need. Paul shares results from his own blinded field study comparing 90 g and 120 g of carbohydrate an hour over 55 km. It found no difference in total time, climbing or descending, but every runner had more gut distress on 120 g after about four hours.
They also cover how Paul builds race plans from lab testing, training files and years of race split times, and why he thinks faster ultra times owe more to better training environments than to race-day fuelling. He explains the everyday gaps he sees most (refuelling after training, protein at breakfast and meeting total energy needs), and why age-group runners may do well starting nearer 60 g an hour and building only if they need to. Paul is careful to say his findings apply to trail and ultra running up to the distances he has tested, not to cycling or triathlon.
Key Topics
- Paul's OCC race: just over 11 hours on a hot day, fuelled at about 60 g of carbohydrate an hour, completing his set of UTMB ultra races
- Caffeine at the elite end, including a CCC podium athlete who took far more caffeine than planned while racing through a knee injury
- Lab testing in heat and altitude chambers to find each athlete's gut ceiling, and using race modelling to find where carbohydrate can come down as well as up
- Why Paul thinks faster ultra performances are driven mainly by more professional, strategic training, and why over-fuelling on race day adds nothing but gut issues
- The risk of pairing very high in-training carbohydrate with "burgers and pizza" to meet energy needs, when fruit, vegetables, fibre, iron and micronutrients still matter
- The most common everyday gaps: delayed refuelling after training, too little protein at breakfast, and under-eating total energy on high-volume days
- Whether 120 g an hour is justified: Paul sees elite intakes settling around 100 g, and reported high intakes are often overstated once discarded gels and bottles are counted
- Paul's 90 vs 120 g field study: no significant difference in time, climbing or descending, with a consistent rise in upper-GI distress on 120 g after about four hours
- Practical advice for age-groupers: start around 60 g an hour, build towards 90 g only if you are comfortable and racing hard
- Glucose to fructose ratios: why 1:0.8 mainly matters above about 90 g an hour, and how sponsor products shape what athletes can take
Chapters
00:00 Introduction
04:02 Paul's OCC race at UTMB week
07:32 Elite race results and caffeine plans
11:52 Lab testing and race modelling
21:47 Why ultra times are getting faster
26:47 Training fuel versus overall diet quality
32:04 Timing, recovery and breakfast protein
34:27 Is 120 grams an hour justified?
41:52 The 90 vs 120 gram field study
53:55 Fuelling advice for age-group runners
56:29 Carbohydrate intake and recovery
1:00:05 The 10 grams an hour argument
1:05:00 Glucose to fructose ratios
1:08:56 Paul's podcast and how to reach him
04:02 Paul's OCC race at UTMB week
07:32 Elite race results and caffeine plans
11:52 Lab testing and race modelling
21:47 Why ultra times are getting faster
26:47 Training fuel versus overall diet quality
32:04 Timing, recovery and breakfast protein
34:27 Is 120 grams an hour justified?
41:52 The 90 vs 120 gram field study
53:55 Fuelling advice for age-group runners
56:29 Carbohydrate intake and recovery
1:00:05 The 10 grams an hour argument
1:05:00 Glucose to fructose ratios
1:08:56 Paul's podcast and how to reach him
Guest / Resources
- Paul Booth on Instagram: @ultra.endurance.nutritionist
- Paul's website, Performance Gains: performancegains.co.uk
- Paul's previous Mikkipedia episode (398): Fueling Tom Evans and Ruth Croft's Victories at UTMB: Inside Elite Ultra Nutrition with Paul Booth
- Plews DJ, Booth PD, Krieger T, Maunder E. Fuelled or Fooled? Examining the Evidence and Mechanisms Behind Ultra-High Carbohydrate Intake in Endurance Athletes. Sports Medicine, 2026
- Paul's 90 vs 120 g per hour field study in ultra runners, presented at the ECSS conference (not yet published)
- O'Brien WJ, Rowlands DS. Fructose-maltodextrin ratio in a carbohydrate-electrolyte solution differentially affects exogenous carbohydrate oxidation rate, gut comfort, and performance. American Journal of Physiology: Gastrointestinal and Liver Physiology, 2011. The origin of the 1:0.8 ratio discussed
- MNSTRY's podcast, which Paul co-hosts: mnstry.podbean.com
- Athletes and people mentioned: Tom Evans, Ruth Croft, Miao Yao, Gemma Hillier-Moses, Rachel Entrekin, Dan Green, Dr Dan Plews, Tim Podlogar, Alistair Brownlee
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Contact Mikki:
https://mikkiwilliden.com/
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NZ listeners - save 10% off Calocurb by using the code Mikkipedia10 at www.calocurb.co.nz
Contact Mikki:
https://mikkiwilliden.com/
https://www.facebook.com/mikkiwillidennutrition
https://www.instagram.com/mikkiwilliden/
https://linktr.ee/mikkiwilliden
