Everyone seems to be chasing 120 grams of carbs per hour at the moment. But the research says that performance actually starts to dip after 100 grams per hour. And the fuelling plan behind two UTMB wins proves it.
Paul Booth is a sports nutritionist, exercise physiologist, and lead nutritionist for the Salomon International Team with 26 years in university academia and 92 ultras completed himself. In 2025 he built the customised fuelling strategies that won both the men's and women's UTMB 100. But what makes this conversation valuable is not what Tom Evans and Ruth Croft did. It is what you can take from it and apply to your next race.
In this episode Paul breaks down exactly how much carbohydrate you actually need per hour based on your intensity and fitness level, why going above 100 grams per hour may actually hurt your performance, how to train your gut so it does not fail you on race day, the glucose to fructose ratio that the research actually supports, and the one fuelling hierarchy mistake most ultra runners are making right now.
Whether you are racing a marathon, a 100k or a 100 miler this is the most practical fuelling conversation you will find.
Paul Booth:
Website: https://performancegainsnutrition.com/
Instagram: @ultra.endurance.nutritionist
Show notes links:
1. Ricardo Costa — Gut Training Research (the key paper Paul references)https://cdnsciencepub.com/doi/abs/10.1139/apnm-2016-0453
2. Ricardo Costa — Gut Training Systematic Review (most comprehensive overview)https://pubmed.ncbi.nlm.nih.gov/37061651/
3. O'Brien and Rowlands — The 0.8 fructose to glucose ratio paper (2011)https://journals.physiology.org/doi/full/10.1152/ajpgi.00419.2010
4. O'Brien and Rowlands — Fructose Maltodextrin Ratio Governs Performance (2013)https://www.researchgate.net/publication/255958218_Fructose-Maltodextrin_Ratio_Governs_Exogenous_and_Other_CHO_Oxidation_and_Performance
5. Alan McCubbin — Sodium ingestion and endurance performance systematic reviewhttps://research.monash.edu/en/publications/impact-of-sodium-ingestion-during-exercise-on-endurance-performan/
0:00 Why 120g/hr has no research behind it
1:11 The UTMB fuelling strategy explained
4:20 What lab testing actually reveals
13:06 How to deliver carbs during a race
16:35 Carb strategy for recreational runners
21:35 Do elites need more carbs than amateurs
28:36 Fuelling the second half of your race
33:30 Gut training and osmolality
38:18 Glucose to fructose ratios
43:05 More carbs does not mean better performance
50:47 Feeding frequency and electrolytes
57:54 The fuelling hierarchy
1:01:13 Final takeaway for your next race
1:03:46 What endurance means to Paul Booth
