Carbohydrate intake and ketosis in self-sufficient multi-stage ultramarathon runners

ABSTRACT

Ultra-endurance athletes accumulate an energy deficit throughout their events and those competing in self-sufficient multi-stage races are particularly vulnerable due to load carriage considerations. Whilst urinary ketones have previously been noted in ultra-endurance exercise and attributed to insufficient carbohydrate (CHO) availability, not all studies have reported concomitant CHO intake. Our aim was to determine changes in blood glucose and β-hydroxybutyrate concentrations over five days (240 km) of a self-sufficient multi-stage ultramarathon in combination with quantification of energy and macronutrient intakes, estimated energy expenditure and evaluation of energy balance. Thirteen runners (8 male, 5 female, mean age 40 ± 8 years) participated in the study. Glucose and β-hydroxybutyrate were measured every day immediately post-running, and food diaries completed daily. CHO intakes of 301 ± 106 g·day⁻¹ (4.3 ± 1.8 g·kg⁻¹·day⁻¹) were not sufficient to avoid ketosis (5-day mean β-hydroxybutyrate: 1.1 ± 0.6 mmol.L⁻¹). Furthermore, ketosis was not attenuated even when CHO intake was high (9 g·kg⁻¹·day⁻¹). This suggests that competing in a state of ketosis may be inevitable during multi-stage events where load reduction is prioritised over energy provisions. Attenuating negative impacts associated with such a metabolic shift in athletes unaccustomed to CHO and energy restriction requires further exploration.

KEYWORDS:

• Ketones
• running
• ultra-endurance
• carbohydrate
• performance
• nutrition
• energy deficit

Acknowledgments

The authors wish to thank the all the participants whose willingness to participate and generosity of spirit in staying with it all until the end is greatly, and gratefully, appreciated. Thanks also go to the management team at Racing the Planet for their enthusiasm for the study and their willingness in allowing the research to take place.

Disclosure statement

No potential conflict of interest was reported by the authors.