Fueling for Runners: Why You Can’t Train What You Don’t Fuel

For a long time, I thought my struggles with training were about discipline. Not enough grit. Not enough toughness. Not enough willingness to suffer. That story is easy to believe in endurance sports, where effort is visible and restraint is often praised. But over the years—especially since my return to single-day ultras and a couple of hard DNFs

—that explanation started to fall apart.

Like most runners, I’ve lived through nearly every nutrition trend that’s come down the pipe. Low-fat. Low-carb. High-fat. Fasted runs. “Train low, race high.” Some of those ideas aren’t wrong. But most of them are applied wildly out of context. And context, as it turns out, is everything.

As a coach, I see the same pattern play out again and again. Athletes—both kids and adults—show up to training under fueled. They grind through workouts. They struggle to recover. They race flat. Then they ask the obvious question: Why am I not improving? The answer is rarely about effort. More often, it’s about energy.

It wasn’t until relatively recently that I became truly intentional about fueling—matching intake to training demand rather than to fear, habit, or trend. When I did, something surprising happened. My performance improved. My consistency improved. My overall fitness improved. Not because I trained harder—but because my body finally had what it needed to adapt.

That shift didn’t come from a single revelation. It came from years of coursework in sports nutrition and performance, self-study in biochemistry and exercise endocrinology, long conversations with other coaches, and a lot of trial and error—some of it costly. It also came from an uncomfortable realization: endurance athletes are not immune to disordered eating. In fact, we may be uniquely good at disguising it as “discipline.”

I share that not for sympathy, but for clarity. Fueling isn’t just about calories or carbohydrates. It’s about honesty—about recognizing that the human body, like a finely tuned engine or a carefully built flame, cannot perform on intention alone. You can’t starve a system and expect it to grow stronger.

And that’s where this conversation really begins

Fat Burns in a Carbohydrate Flame

One of the most useful concepts I ever learned in a sports nutrition course was a simple phrase:

“Fat burns in a carbohydrate flame.”

At first glance, it sounds like a slogan. But it isn’t. It’s biochemistry.

Runners are often told they need to “burn more fat” to improve endurance or lose weight. That advice isn’t wrong—but it’s incomplete. The body does not choose between fat or carbohydrate. It relies on both, working together inside a tightly regulated metabolic system.

Fat is an abundant fuel source. Even lean athletes carry tens of thousands of calories of stored fat. But fat is slow-burning. For it to be broken down efficiently and converted into usable energy, the body requires carbohydrate-derived intermediates that keep the aerobic energy system running smoothly. When carbohydrate availability drops too low, that system begins to falter—not because fat disappears, but because the flame that allows it to burn steadily grows unstable.

This is where many runners get tripped up.

When carbohydrate intake is chronically restricted—whether intentionally or unintentionally—the body can still function, but it does so at a lower ceiling. Intensity becomes harder to access. Perceived effort rises. Recovery slows. Training sessions that should feel controlled begin to feel labored. The runner interprets this as a lack of fitness or toughness, when in reality it’s a lack of fuel.

A helpful way to think about this is to imagine the human body as a highly sophisticated candle. Fat is the wax—long-lasting, energy-dense, slow to melt. Carbohydrates act more like the wick and stabilizer, helping regulate how cleanly and efficiently that wax is converted into light and heat. Without enough carbohydrate, the flame flickers. The candle still burns, but not well. Soot builds. Efficiency drops. The system becomes fragile.

This matters because endurance training isn’t just about completing miles—it’s about adaptation. The aerobic system improves when it is repeatedly stressed and then allowed to recover. That recovery process is energy-dependent. Without sufficient carbohydrate, the body struggles to restore glycogen, regulate hormones, and support the cellular remodeling that actually makes a runner fitter.

In other words, you can’t train fat metabolism by starving the system that allows it to function.

This doesn’t mean runners need to consume sugar constantly or abandon all structure around nutrition. It does mean that fueling choices must be made in context—relative to training volume, intensity, and experience level. What might be a useful strategy for a well-trained athlete can become a limiting factor, or even a risk, for someone still building their aerobic base.

And that distinction—between strategy and habit—is where most problems begin.

Fueling for Runners: Why Context Matters More Than Rules

One reason sports nutrition advice feels so contradictory is that it often answers the wrong question.

Are you trying to be healthy? Are you trying to be fit? Or are you trying to perform?

Those three goals overlap—but they are not the same. And they do not require identical fueling strategies.

Health

Fueling for health prioritizes:

• Metabolic stability

• Long-term energy balance

• Blood sugar regulation

• Sustainability across decades

For someone whose primary goal is general health, occasional fasted runs, lower-intensity training, and conservative carbohydrate intake may be perfectly appropriate. The system is stressed lightly. Recovery demands are modest. The flame burns low and steady.

Fitness

Fitness lives in the middle ground. This is where most recreational runners sit—even if they don’t realize it.

Here, fueling must support:

• Repeated training sessions

• Progressive overload

• Consistent recovery

• Adaptation over weeks and months

This is also where mistakes become costly. Under fueling doesn’t just slow improvement—it distorts feedback. The runner trains tired, recovers incompletely, and begins to confuse fatigue with lack of talent or motivation. Progress stalls, not because the work isn’t being done, but because the system can’t absorb it.

Performance

Performance asks a very specific question: How good can I be at this, right now?

Fueling for performance is unapologetically intentional. Carbohydrates are not optional. They are structural. They support training quality, hormonal regulation, neuromuscular output, and recovery between hard sessions. This isn’t indulgence—it’s engineering.

Problems arise when athletes try to pursue performance outcomes while fueling as if their goal were weight loss or metabolic minimalism. That mismatch creates frustration, injury, and eventually burnout.

You can’t ask the candle to burn brighter while trimming the wick.

Where Runners Get Stuck

Many runners unknowingly live in contradiction. They train like performance athletes, fuel like dieters, and hope for health as a byproduct. The body responds predictably: inconsistency, fatigue, stagnation.

The goal of fueling isn’t to eat more or less. It’s to align intake with intent.

That alignment requires attention—not perfection.

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At this point, I want you to pause and consider the following questions.  These aren’t intended to just be answered once.  Reflect on them often throughout your training journey - the answers will change over time:

• What am I actually training for right now—health, fitness, or performance?

• Do my fueling habits support that goal, or quietly undermine it?

• Am I using nutrition as a strategy—or as a form of control?

• After most runs, do I help my body adapt… or just survive?

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The Question Everyone Asks—and the One That Matters More

At some point, every nutrition conversation arrives at the same place.

“Okay, Coach—but what exactly should I eat?”

It’s a fair question. It’s also the wrong one.

The idea that there is a perfect food, a perfect ratio, or a perfect plan that guarantees performance is deeply appealing. It suggests certainty. Control. A simple exchange: eat this, get that. But human physiology doesn’t work that way—especially under the variable stress of endurance training.

Sports nutrition is not a formula. It’s an ongoing experiment.

Your body is not static. Training load changes. Stress changes. Sleep changes. Seasons change. Even your ability to tolerate certain foods can shift over time. The goal of fueling, then, is not precision—it’s responsiveness.

What matters most is not what you eat on any given day, but whether your choices consistently support the work you are asking your body to do.

That requires attention, not rigidity.

Sound Principles That Actually Hold Up

Rather than chasing rules, runners are better served by a few durable principles:

• Fuel supports training, not the other way around. If training quality is falling, nutrition deserves scrutiny before motivation does.

• Carbohydrates are functional, not moral. They are neither good nor bad. They are a tool—one that becomes increasingly necessary as training volume and intensity rise.

• Restriction creates noise. Chronic under fueling distorts feedback. It becomes difficult to tell whether fatigue reflects fitness, stress, or simple energy deficiency.

• Consistency beats optimization. The best fueling strategy is the one you can repeat without friction or obsession.

• Awareness outperforms control. Counting every calorie or gram may look disciplined, but it often disconnects athletes from hunger, recovery, and intuition. Mindful patterns scale better than strict rules.

These principles don’t tell you exactly what to eat—and that’s intentional. They guide decision-making instead of replacing it.

Fueling Is a Practice, Not a Prescription

The most effective athletes I’ve coached are not the ones with the tightest rules. They are the ones who pay attention. They notice patterns. They adjust. They experiment carefully and reflect honestly.

They understand that fueling is not about perfection—it’s about alignment.

Alignment between:

• Training demand and energy availability

• Short-term goals and long-term health

• Effort and recovery

When that alignment is present, progress feels steadier. Training becomes more repeatable. Confidence grows—not because everything is controlled, but because the system is supported.

And that’s the quiet truth behind all of this:

You can’t train what you don’t fuel—but you also can’t fuel well without paying attention.

That’s the work. And it’s worth doing.

A Few Things to Notice on Your Next Run

Rather than changing what you eat right away, try changing what you notice.

Fueling decisions become much clearer when they’re grounded in lived experience instead of theory. On your next few runs or training sessions, see if you can pay attention to the following—not to judge or correct, but simply to observe.

Before the Run

• Do I feel prepared or merely willing?

• Am I carrying a sense of quiet readiness—or low-grade fatigue?

• Does my body feel fueled… or braced?

Preparation has a feel to it. Over time, you’ll learn the difference between showing up ready and showing up depleted.

During the Run

• Does effort rise smoothly—or spike unpredictably?

• Can I access different gears, or does everything feel stuck at one speed?

• Is my breathing steady, or am I working harder than the pace suggests?

Well-fueled systems tend to feel responsive. Under fueled systems feel brittle—either flat or frantic, with very little in between.

After the Run

This is where the real information lives.

• How quickly do I feel like myself again?

• Am I pleasantly worked… or completely drained?

• Do I feel capable of training again tomorrow—or relieved that I don’t have to?

One of the most meaningful shifts I experienced when I became more intentional about fueling—particularly carbohydrate intake—was how I felt after training. I wasn’t wrecked. I wasn’t overly sore. Recovery happened faster. I could go again.

That wasn’t luck. It was feedback.

Let the Body Teach You

Performance doesn’t announce itself during the workout. It reveals itself in recovery—how resilient you feel, how repeatable your training becomes, how often you can show up without forcing it.

You don’t need to count, track, or optimize everything to learn these lessons. You just need to pay attention long enough for patterns to emerge.

Fueling isn’t about control. It’s about support. And support, done well, feels surprisingly calm.

That calm—the ability to train, recover, and return—is often the clearest sign that you’re finally giving your body what it needs.

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