The Art of Fueling for an Ultramarathon Before, During and After the Race

Originally posted on Outdoors on SI | By Sean Langan | Last updated Jul 21, 2025 8:00 PM ET

Dubbed "The Race Across the Sky", this is a historic, yet brutal 100-mile footrace in the Rocky Mountains. This year's edition of the Leadville 100 takes place on August 16th, meaning most athletes are in the peak of their training (or should be).

As if 100 miles by itself wasn't enough, runners must manage over 18,000 feet of elevation gain and tackle Hope Pass not once, but twice, given the out-and-back format, which brings them to a peak elevation of 12,600 feet, where the air is thin. In the 2024 edition, David Roche shattered the course record in 15 hours and 26 minutes, while Mary Denholm put together a fantastic race in 18:23, threatening the female course record that has stood since 1994.

Roche's nutritional exploits, in particular, have brought attention to the physical demands of these races and the importance of fueling for high performance. Per his Instagram, the strategy was to "slurp carbs like my life depended on it", which ended up amounting to a whopping ~8,000 calories.

How Many Calories Does a 100-mile Ultra Race Require?

During the Wasatch Front 100 in Utah, which has a bit less climbing than Leadville, two experienced runners burned 16,000 calories when it was all said and done (33 hours), and were able to replenish about half of that during the race. For reference, Roche ate a similar total amount at Leadville, but in less than half the time.

What's interesting is that in the 24 hours after the race, their bodies were still burning 4-5,000 calories without exercising. That's far above normal levels for adult men of their size (~2,500 calories per day). After seven days, they started to return to normal, but the effects of the race were still lingering.

These races are highly technical and involve tons of uphill/downhill running, which tends to cause substantial muscle damage. What we're seeing is the body trying to recoup its losses, which seems to take the better part of a week. To fully recoup those losses, the runners would have to eat an additional 1,000+ calories per day in the following week to establish some normalcy.

All in all, if we include the recovery week (8-9 total days), the physical cost of running a 100-mile mountainous ultra is over 40,000 calories! Usually, that wouldn't be impressive over 9 days of daily training. However, we're talking about only 1-2 days of exercise, and from my experience, a relatively sedentary week that follows. Nevertheless, the body continues to burn calories as if it were exercising each day.

Train Hard, Recover Hard

If you're one of the select few tackling Leadville next month, I salute you. As one of the most storied ultras in the world, it's the "ultimate test of Grits, Gut, and Determination". Be sure to visit their website for information on race support and aid stations to keep you fueled and healthy for a great day (or 2) in the mountains. Once you're done, rejoice in the fact you can have at least a week of your favorite snacks, guilt-free, because your body will need it!

This article first appeared on Outdoors on SI and was syndicated with permission.

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