Long Run Fueling: What Actually Works

The Mistake I See Every Sunday

It's almost always the same pattern: the athlete starts strong, feels great for the first 45 minutes, and somewhere between mile 9 and mile 12 everything falls apart. Heavy legs, mental fog, the overwhelming urge to walk. The first question I ask isn't about pace. It's: "What did you eat during the run?"

The answer, more often than not, is "nothing" or "one gel halfway through, just in case."

The long run isn't just the cornerstone of aerobic training — it's also the lab where your race-day fueling strategy gets built. And that's exactly where most runners leave performance, and comfort, on the table.

Why Carbohydrate Matters So Much in Long Efforts

During prolonged exercise, muscle and liver glycogen deplete progressively. When that happens, the body leans more heavily on fat oxidation, which is a slower fuel to mobilize and less efficient for sustaining intensity. The practical result: pace drops, perceived effort climbs, and your ability to make good decisions — pacing, hydration, nutrition — gets worse right when you need it most.

This isn't just a subjective feeling. The metabolic stress of a prolonged effort leaves measurable traces — biochemical markers of muscle damage, inflammation, and oxidative stress that rise with the duration and intensity of exercise [PMID:41922043]. Fueling properly doesn't eliminate that stress, but it does help you sustain the intensity you planned for and recover better afterward.

It's also worth a quick reality check: cardiovascular risk during endurance running is low in absolute terms, but it isn't zero, and the prolonged strain placed on the cardiovascular system — especially in older runners — is an active area of research [PMID:31321073] [PMID:40667749]. This isn't a reason for alarm, but it is one more reason to train the body progressively, including how we fuel it during effort.

The Baseline: 45–60 Grams of Carb Per Hour

The number I use as a starting point with my athletes is 45–60 grams of carbohydrate per hour of continuous effort. That's not an arbitrary figure — it's consistent with what exercise physiology research shows about exogenous carbohydrate oxidation rates and gastrointestinal tolerance in trained runners.

But this number comes with important nuance:

It depends on duration. For runs under 75 minutes, many runners don't need extra fuel if they showed up well-fed — stored glycogen is usually enough. Past the 75–90 minute mark, the curve shifts, and exogenous carbohydrate starts making a real difference in pace maintenance.

It depends on gut training. The gut is trainable, just like your legs. A runner who has never practiced taking in carbohydrate while moving might struggle with 30 g/h, while someone with months of practice can tolerate 90 g/h or more using glucose-fructose blends (which use different intestinal transporters and get absorbed in parallel).

It depends on intensity and heat. At higher intensity and higher temperatures, blood flow gets redirected toward the skin and working muscles, and digestive tolerance tends to drop. On hot days, many athletes tolerate less concentrated carbohydrate and need to dilute more or space out their intake.

So the 45–60 g/h range is a reasonable starting point to validate in training — not a fixed prescription for everyone.

When to Start Fueling

This is the question I get asked most, and the short answer is: before you need it.

Waiting until you feel hungry, fatigued, or "bonky" during the run is waiting too long — by that point glycogen has already dropped and you're playing catch-up, which is exactly the kind of thing the gut handles poorly under stress.

My general recommendation:

• Runs of 60–75 minutes: fueling isn't mandatory, but practicing a small intake around the 40–45 minute mark is useful if you're training for a marathon.
• Runs of 90 minutes or more: start between minutes 20 and 30, and continue at regular intervals (roughly every 20–25 minutes) instead of waiting until you feel bad.

The logic is simple: maintaining stable blood glucose is easier than correcting a drop that's already happened.

What to Test in Training — Never for the First Time on Race Day

This rule is non-negotiable in my programming: everything you plan to use on race day needs to be tested first, multiple times, during long runs.

That includes:

• The specific product (gel, chew, drink, or a combination)
• The amount per hour
• The frequency of intake
• How it pairs with hydration and electrolytes
• How your stomach handles that product at race pace, not just easy-run pace

A product that works perfectly on an easy run can behave very differently at marathon pace, when there's less blood flow available for digestion. That's why I build in at least two or three long runs with race-pace segments specifically to test the fueling plan under realistic conditions.

Two Simple Examples

90-minute long run: Light breakfast 2–3 hours beforehand. At 25 minutes, first intake of roughly 20–25 g of carbohydrate (half a gel or a handful of chews). Second intake at 50 minutes, similar amount. If the pace is moderate and the weather is mild, that's usually enough — you don't need to hit 60 g/h for an effort of this length unless you're specifically simulating race conditions.

2-hour long run: Same setup, but now with three to four intakes spaced every 25–30 minutes, targeting a total of 45–55 g/h. For example: a full gel at 25 minutes, chews at 50 minutes, a gel at 75 minutes, and one last small intake around the 100-minute mark if the pace is demanding. Hydration runs in parallel, adjusted for heat and your individual sweat rate.

The point isn't to memorize the example — it's to replicate the structure, adjusting amount and product to what your gut actually tolerates well.

Henri's Take

There's a tendency to talk about fueling in terms of restriction, or "I need to burn more than I eat." That's not coaching, that's noise. Carbohydrate during effort isn't a reward or a luxury — it's functional fuel that lets you train with the quality your plan demands. I think about it the same way I think about sleep or recovery: it's not optional if you want to perform consistently.

I've also seen, in my own training for the 3000m on the track, that the discipline of testing things in practice — not just fueling, but shoes, warm-up routine, hydration — is what separates runners who show up calm on the start line from those who show up guessing.

If you're building your long run plan and aren't sure where to start with nutrition, check out the Runner's Glossary in the nutrition section — I break down terms like exogenous carbohydrate, gut training, and sports drink osmolality there, which will help you understand every decision you make out on the road.

Key Takeaways

• Use 45–60 g/h of carbohydrate as a starting point, but adjust it based on duration, intensity, heat, and your own gut training.
• Runs under 75 minutes usually don't require extra fuel; past 90 minutes, exogenous carbohydrate really does matter.
• Start fueling between minutes 20–30, not once you already feel the bonk coming.
• Test every product and amount in training, especially during race-pace segments — never for the first time on race day.
• Fueling exists to support performance and sustain training, not as a matter of restriction.

References

• Siebers M, Bizjak DA. Exercise biomarkers. Adv Clin Chem. 2026. [PMID:41922043]
• Dayer MJ, Green I. Mortality during marathons: a narrative review of the literature. BMJ Open Sport Exerc Med. 2019. [PMID:31321073]
• Frandsen J, Aaroe M. Cardiac Effects of Prolonged Endurance Exercise in Young and Older Athletes. Scand J Med Sci Sports. 2025. [PMID:40667749]