Optimal Energy for Ultra Runners & Long Distances (#188)

Several studies on ultrarunners have measured energy expenditure using validated methods and arrived at a simple conclusion: Higher physical demands increase energy consumption. Obviously — but the research also provides more concrete figures for different types of ultra races:

• 3831–4999 kcal/day — 225 km over 5 days, varied terrain (Al Andalus Ultimate Trail) and 32–40 °C. Participants: 46 males and 28 women, 60–80 kg and 30–50 years old.
• 4764–5654 kcal/day — 305 km over 8 days, mountain marathon, cold to moderately warm (unknown race and temperature).
• 6000–8000 kcal/day — 250 km over 5 days in a lab on a treadmill with incline, room temperature.
• 18000 kcal/day — 24-hour trail ultramarathon where participants ran 122–208 km.

On the surface, the numbers vary significantly, but if we divide the energy expenditure by hours spent on the course, we average around 550 kcal/hour over a 24-hour period. Keep that number in mind when planning your energy intake — but we'll dive deeper into the nutrition rabbit hole below.

During ultra distances, we can often maintain energy balance over time, enabling us to keep going for several days. Experts highlight some key guidelines:

1. Energy Balance – If you burn around 550 kcal/hour, aim to consume as close to that energy amount as possible without compromising your performance.
2. Total carbohydrate intake should be approximately 12 g of carbohydrate per kilogram of body weight per day.
3. Protein intake should be between 1.6–1.8 g/kg of body weight per day.
4. Fat intake serves to achieve energy balance when carbohydrate and protein targets are met; fats typically represent 20-35% of total daily energy.

Reaching protein targets can be tough if you're carrying everything yourself during the race. In that scenario, reduce protein intake to around 1.2 g/kg to save on weight and space in your pack.

1–4 hours before the start: consume 1–4g of carbohydrate per kg of body weight. Opt for foods you know are "gut-friendly" — avoid those that are high in fat, fiber, sugar alcohols, protein, and fermentable starches in the days leading up to the race. If you want to learn more about FODMAP, we have an article on it: https://www.presteramera.com/lugnare-mage-med-fodmap/

Note: the stomach can be trained to tolerate more energy, particularly carbohydrates, during activity. Continuous carbohydrate supply without gut issues is essential — because if the stomach fails, you also lose fluids. We have a guide for 4-week gut training here: https://www.presteramera.com/tavlingsklar/ — and a study showed that a 2-week program reduced gut issues by 60–63% and improved performance in a 2-hour running test by 4–5% (https://www.ncbi.nlm.nih.gov/pubmed/28177715).

The biggest challenge in practice is logistics: many races require carrying your own energy, which adds several kilos to your pack (fluid + food).

In 24–36 hour races, intake studies show a consumption of 36–63% (on average 50%) of expenditure. Higher intake often correlates with better placement, but not always—training and other factors come into play. However, all else being equal, those who refuel more tend to place better. Yes, there's a certain macho culture in the ultra-running world too—but the fuel helps.

The classic recommendation for carbohydrates during ultra-running is 90 g carbohydrates per hour.

“Nevertheless, for ultramarathon running, where duration is typically >4 hr, it is generally recommended to consume 90 g·kg−1 of a multiple-transportable carbohydrate blend (e.g., 2∶1 glucose–fructose ratio).”

In reality, few reach this: ad libitum reports show that ultrarunners often take in only 20–40 g of carbohydrates per hour, even though they carry enough for 60 g/hour. Ultrarunners are generally poor at following recommendations—but when everyone is equally bad, it rarely becomes the biggest explanation for performance. Still, try not to make it a contest of toughness to avoid energy.

The longer you're out there, the more you benefit from high fat oxidation. The main driver for increased fat oxidation is training—long sessions build your capacity. While dietary manipulation (like having low-carb days) does have some effect, it pales in comparison to the impact of training.

Theoretically, an ultrarunner who oxidizes 1.2 g of fat per minute could draw nearly 700 kcal/hour from their fat stores—this is beneficial in races that go beyond 10 hours at 45–70% of VO2max. However, it's debated whether increased fat oxidation actually boosts performance. Studies rarely show clear performance improvements solely through increased fat oxidation.

Initiatives like the Supernova project explore combinations: first max out fat oxidation, then follow it with high carbohydrate intake to see if both systems can be simultaneously optimized. The preliminary results are encouraging.

Your peak fat oxidation—the intensity at which your body provides the maximum amount of fat to your muscles—seems to be around 65–70% of VO2max. In a study involving 15 males, fat utilization at 60% VO2max varied from 0.8 to 1.7 g/min with a balanced diet (20% protein, 52% carbohydrate, 28% fat) along with a simultaneous intake of 90 g carbohydrates/hour.

“A recent study (n = 15 men) found a wide range of maximal fat oxidation rates (mean: 68% (95% confidence interval [61–74%] VO2max) and steady‑state fat oxidation rates (0.8–1.7 g/min) over 3 hours of running at 60% VO2max (mean ± SD: 10.0 ± 1.2 km/hr), while following a macronutrient-balanced diet (20% protein, 52% carbohydrate, and 28% fat) and consuming carbohydrates during exercise (90 g/hr, 2:1 glucose–fructose 10% wv; Rauch et al., 2018).”

So, there's no universal method to boost fat oxidation—and the question is whether it's worth spending too much time on it. Many runners can oxidize up to 1.7 g/min while consuming 90 g carbohydrates/hour. If you max out carbohydrate intake and your body efficiently uses fat too, it's often mechanical and mental fatigue, not a lack of energy, that slows you down.

Research indicates that thirst is a reliable cue for when to drink, provided the exertion level is relatively low (such as during an ultramarathon) and the temperature is under approximately 30 °C. Drink according to your thirst and avoid overconsumption.

Interesting area: Research suggests that extra salt supplements are unnecessary in a low-intensity sport like ultrarunning — even in the heat. Salt tablets are not recommended if you consume regular sports nutrition via sports drinks, gels, energy bars, salty crackers, soups, and more available at aid stations.

“It has, however, been demonstrated that supplemental sodium is not necessary to maintain euhydration during ultramarathon competition, even under hot ambient conditions (Hoffman et al., 2015). Thus, best practice suggests avoiding attempts to replace all sodium lost in sweat through sodium supplementation during ultramarathon running, recognizing that considerable sodium is present in the typical race diet (e.g., electrolyte beverages, sports bars and gels, savory sandwiches, crisps, pretzels, and soups).”

Base your approach on 550 kcal/hour as a reasonable benchmark for energy expenditure, and aim to compensate as much as possible. As mentioned, most people only compensate up to about half of their consumption during ultra-distance races. With 550 kcal/hour, that translates to roughly 275 kcal/hour in intake, which is approximately 65–70 g of carbohydrates per hour.

Some energy comes from protein and fat, so your actual carbohydrate intake is likely around 60 g/hour or less in practice. But if you manage to consume 60 g/hour, choose gut-friendly foods during breaks, and drink according to your thirst — then you've covered 99% of the nutrition job. The remaining part is training and mental toughness.

Have an Awesome time and enjoy your long runs. Remember, these sessions build your fat oxidation the most — even if you consume up to 90 g of carbohydrates per hour during the session. There's no quick fix; training combined with a smart nutrition strategy is the way forward.

Good luck out there — and don't forget that sometimes it's okay to be a little kind to your stomach.