Over the past few weeks, we’ve meticulously built and organized our Fueling Playbook. We’ve identified our Pillars, our Rotational Players, and our Test Kitchen items. Now, we will look at the math behind the strategy. To be a successful ultrarunner, you must become a master of energy management. There is an unbreakable rule in this sport: you cannot outrun a massive calorie deficit.

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This is part of a series of posts regarding how we prepare, plan, and train to complete the 100-mile Ultramarathon Umstead 100. Our series for this event: Collecting Laps: one lap at a time to 100. For all the ultrarunning series, here, follow the link. Training for a 100. Alternatively, you can also follow our Podcast so you don’t miss the weekly summary post.

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Think of your body’s energy like a bank account. You have a “checking account” of glycogen—readily available carbohydrate stored in your muscles and liver—that holds at best about 1,600 calories. It’s easy to access but quickly depleted. You also have a massive “savings account” of fat, which holds tens of thousands of calories. This energy is abundant, but harder and slower to access. A 100-mile race will empty your checking account many times over. Your job is to make consistent deposits (i.e., eat) while also training your body to efficiently make withdrawals from savings (burn fat).

Assessment:

Let’s do some simple math to understand the scale of the challenge. This is the Ultrarunner’s Energy Equation.

1. Calculate Total Burn: A conservative estimate is 110 calories burned per mile.
   • 100 miles × 110 calories/mile = 11,000 calories burned
2. Subtract Your Starting Glycogen: You begin the race with a full “checking account.”
   • 11,000 calories burned - 1,600 stored calories = 9,400 calorie deficit
3. Factor in Your Fat-Burning “Savings Account”: Here’s where your training pays off. A well-trained ultrarunner can derive 30-50% of their energy from fat. Let’s be conservative and use 40%.
   • 9,400 calorie deficit × 40% = 3,760 calories from fat
4. Determine Your Target Replacement Goal: This is the number of calories you need to consciously consume during the race.
   • 9,400 calorie deficit - 3,760 calories from fat = 5,640 calories to replace

Suddenly, the task seems manageable to plan and execute. You don’t need to replace all 11,000 calories. You need a strategic plan to ingest around 5,640 calories. This is where your A, B, and C lists come into play. A sample plan to get to 5,640 calories might look like this:

1,490 calories from real food (your B-list, C-List, potatoes, soup, sandwiches, quesadillas at aid stations)

2,425 calories from liquids (your A-list, B-List, Tailwind, sports drinks)

1,725 calories from gels/chews (your A-list, B-List, staples)

Planning:

Your energy plan is executed in three phases. Practice them all.

Your primary plan should be to consume calories every 30-45 minutes, without fail. Set a repeating alarm on your watch. Even if you don’t feel hungry, you must eat. Thirst and hunger are signals that you are already behind. Use course landmarks (like Cemetery Hill, Five Turn Hill, Water Fountains, turnarounds at Umstead event route) as secondary reminders, but let the clock be your main guide.

The Loading Phase (Days Before): In the 2-3 days before a key long run or race, focus on topping off your glycogen stores. This doesn’t mean mountains of pasta. It means prioritizing familiar, easily digestible carbohydrates as the primary component of your normal meals. You want to start closer to the 1,600 calories storage.

The Top-Off (Race Morning): Execute your practiced, proven pre-run protocol. A simple breakfast 2-3 hours before the start, and maybe a 100-calorie gel or snack 15 minutes before the gun goes off. You want to start with a full tank and a little something already working in the pipeline.

The Execution (During the Run): This is where races are won and lost. You must have a disciplined approach to consuming calories. The most reliable method for most is time-based fueling. Your stomach doesn’t really know miles; it might know time.

Diabetes Learning Notes:

For a Type 1 athlete, our energy equation has a critical extra variable: insulin. Insulin is the gatekeeper to our glycogen “checking account.” Without proper insulin management, we can’t effectively use the fuel we consume. Our goal is not just calorie replacement; it is achieving glycemic stability while fueling performance.

When you perform your Assessment, the math is a starting point. Your true goal is to find the 5,640 calories that have the most predictable impact on your blood sugar. Look at your A-List. Which fuels give you steady energy versus a sharp spike? A 100-calorie gel that sends your BG from 120 to 250 is not a success; it’s a liability that will cost you energy and performance later. Your plan should be built around foods from your A-list that you know you can manage effectively.

In the Planning phase, a time-based and glucose-reading fueling strategy is non-negotiable for us.

Think of your fuel as having two distinct jobs: energy and management. Some carbs are “free”—their glucose will be burned immediately by your muscles’ activity. Other carbs will be needed to offset your basal insulin or to treat a developing low. Your time-based plan ensures you are constantly supplying fuel for both jobs, which is the key to preventing the wild glycemic swings that can derail a race. Your plan must be proactive, not reactive.

Eating on a strict 30-45 minute schedule creates a predictable, steady stream of carbohydrates, but it will depend on the amount of effort you are exerting during that time. This is infinitely easier to manage with basal rates and correction boluses than an erratic intake based on just hunger.

This week’s actual numbers:

Week 20	Mon	Tue	Wed	Thur	Fri	Sat	Sun	Total
Plan	Stretches & Rolling	5	5	6	Rest	13	16	45
Actual	Sickness	Sickness	Sickness	3	Rest	14

Next Week Plan:

Week 19	Mon	Tue	Wed	Thur	Fri	Sat	Sun	Total
Plan	Stretches & Rolling	5	5	6	Rest	15	18	49