Fat: the Ultra-Distance Fuel? Part Two - Too Many Carbs, Not Enough Fat? — Acier | Ultra Distance Endurance Bikepacking Self-Supported Cycling Coaching & Consulting.

During ultra-distance events, the human body requires a huge amount of energy to fuel the millions of muscle contractions required to reach the distant finish line. Energy deficits reaching around 7,000 calories per day in events lasting at least 6 hours have been reported by Nikolaidis et al. (2018). Without addressing this negative energy balance, performance will clearly suffer, before considering the health consequences. Accordingly, Black et al. (2012) observed 18 cyclists during a 384 km race and found a significant negative relationship between energy intake and time taken to complete the race. Attempting to balance out this energy deficit is therefore a big deal.

The Energy Deficit

Nikolaidis et al. (2018), in their review of scientific literature on nutrition in ultra-endurance sports highlight that the current research has concluded that ultra-endurance athletes do not consume sufficient food and drink. The resulting negative energy balance during races manifests as reduced post-race body mass and body fat percentage. The longer the event, the more pronounced the deficit as illustrated by the below chart from their paper presenting energy balance deficits in different sports of varying duration, as well as the energy deficit per hour.

Nikolaidis et al. (2018): Total energy deficit and energy deficit per hour for ultra-endurance sports of various durations.

Geesmann et al. (2014) studied 14 athletes participating in a 1,230 km ultra-endurance bike marathon which took on average 47 hours to complete. In 12 of the 14 athletes, energy intake was lower than expenditure with the average deficit being around 6,000 kcal for the duration. An interesting finding was that energy intake decreased significantly after 618 km, leading to this failure for the participants to maintain an energy balance in the second half of the event. The authors suggest that nutritional recommendations for ultra-endurance athletes may not be followed due to factors such as satiety, gastrointestinal discomfort, and fatigue.

Macronutrient Breakdown

Returning to the Nikolaidis et al. (2018) review, they make what should be an obvious point that, in order to finish an ultra-endurance race, optimal energy and fluid intake is crucial. Digging further into what composes that ‘optimal’ energy intake, they looked at which studies have separated the proportional contribution of carbohydrates, fat and protein to the total energy intake in ultra-endurance events. It is clear that for all sports, athletes rely mostly on carbohydrates for their energy intake. On the whole, around 68% of energy intake for ultra-endurance athletes was through carbohydrates, although of the three cycling events identified, this was closer to 80%.

As for the consumption of fat, this was around 19% across all ultra-endurance athletes. However, in one of the studies (Bircher et al., 2006) of what the authors describe as an ‘extreme’ endurance cycling race - the XXAlps 2004 (2,272 km / 55,455 m completed in 5 days and 7 hours), the athlete only derived 12.7% of their 51,246 kcal energy intake from fat. This resulted in an energy deficit of 29,554 kcal, a reduction in fat mass of 790g and a reduction in fat free mass of 1.21kg.

Nikolaidis et al. (2018): Intake of carbohydrates, fat and protein observed during ultra-endurance cycling, running and triathlon races.

The 4,701 km event in the above chart corresponds to the case study carried out by Knetchle et al. (2004) of the energy intake and expenditure of a male competitor at Race Across America (RAAM). Although an n=1 study, their findings are instructive:

Average distance per day: 470 km
Average climbing per day: 2,582 m
Total energy expenditure: 179,650 kcal
Average energy expenditure per day: 17,965 kcal
Average energy ingested per day: 9,612 kcal
Average daily energy deficiency: 8,352 kcal
Total energy deficiency: 83,526 kcal

This athlete subsequently lost 5kg of body weight during the event, although whether this was fat or muscle was not reported.

Of particular interest is the proportion of macronutrients that this athlete ingested to account for his average 9,612 kcal daily diet:

*Macronutrient breakdown of the energy*
*intake of a cyclist participating in RAAM.*
*Study conducted by Knetchle et al. (2004).*

Can Fat Reduce the Deficit?

In each of these studies there is a clear pattern. Ultra-distance athletes are primarily relying on carbohydrates to fuel their endeavours but are consistently reporting significant energy deficits. Black et al. (2012) make the observation that there are clear difficulties in meeting the high energy demands of ultra-distance cycling and that reducing this deficit is advantageous due to the evident relationship between energy intake and performance. They also note that, given the emphasis has been placed on carbohydrate intake and energy deficits are still present, increasing energy intake from fat should be investigated as a means to reduce this deficit.

Tiemeier et al. (2024) in their recent narrative review of ultra-cycling also comment that, although many ultra-cyclists are already focusing on maximising their carbohydrate stores before and after races as well as consuming carbohydrate-rich foods, an energy deficit is still frequently observed. They conclude by stating that the optimum nutritional supply to reduce this energy gap is yet to be determined and should be adapted to individual race durations and conditions.

We could therefore legitimately ask the question whether increasing fat consumption in ultra-distance events, both as a percentage of overall energy ingestion and as a way to increase absolute intake, could be key to reducing the observed energy deficits. Nikolaidis et al. (2018) certainly suggest so, pointing out that, compared with simple ‘endurance’ sports that rely mostly on the metabolism of carbohydrates, ultra-endurance sports present increase demands in fat intake due to the length of races and the larger amounts of fat stored in the human body compared to carbohydrates. This allies with the conclusion of the first part of this series, where we saw that fat is relied more upon to fuel efforts which are longer in duration and lower in intensity.

The next article will explore the potential benefits of relying more on fat as a fuel for ultra-distance efforts, what the constraints may be and how this could be applied practically.

References

Bircher S, Enggist A, Jehle T, Knechtle B. Effects of an extreme endurance race on energy balance and body composition - a case study. J Sports Sci Med. 2006 Mar 1;5(1):154-62. PMID: 24198693; PMCID: PMC3818668.

Black, K. E., Skidmore, P. M., & Brown, R. C. (2012). Energy Intakes of Ultraendurance Cyclists During Competition, an Observational Study. International Journal of Sport Nutrition and Exercise Metabolism, 22(1), 19-23.

Geesmann B, Mester J, Koehler K. Energy balance, macronutrient intake, and hydration status during a 1,230 km ultra-endurance bike marathon. Int J Sport Nutr Exerc Metab. 2014 Oct;24(5):497-506. doi: 10.1123/ijsnem.2013-0169. Epub 2014 Mar 25. PMID: 24668685.

Knechtle, Beat & Enggist, Andreas & Jehle, T. (2005). Energy turnover at the Race Across AMerica (RAAM) - a case report. International journal of sports medicine. 26. 499-503. 10.1055/s-2004-821136.

Nikolaidis PT, Veniamakis E, Rosemann T, Knechtle B. Nutrition in Ultra-Endurance: State of the Art. Nutrients. 2018 Dec 16;10(12):1995. doi: 10.3390/nu10121995. PMID: 30558350; PMCID: PMC6315825.

Tiemeier, L., Nikolaidis, P.T., Chlíbková, D. et al. Ultra-Cycling– Past, Present, Future: A Narrative Review. Sports Med - Open 10, 48 (2024). https://doi.org/10.1186/s40798-024-00715-7

Fat: the Ultra-Distance Fuel? Part Two - Too Many Carbs, Not Enough Fat?

Fat: the Ultra-Distance Fuel? Part One - Substrate Utilisation.