What to eat, drink, and time around runs so your engine has fuel when it needs it.
Fueling covers what a runner eats and drinks, day to day and mid-run, to keep glycogen stores full and the gut cooperating under load. It ranges from the boring-but-decisive daily basics to the increasingly precise carb-per-hour math that separates a comfortable finish from a wall at mile 20. The research below moves from foundational to race-specific, but the through-line is consistent: most fueling problems show up as pace drift and rising heart rate late in a run, and they're fixed by adjusting intake before the next session, not by willpower during it.
For most runners, especially beginners, the biggest lever isn't a pre-run snack or a race-day gel — it's what gets eaten the other six days a week. Carbohydrate needs scale with training volume, roughly 5–7 g/kg daily for an hour of running a day, climbing to 6–10 g/kg as volume rises toward one to three hours. Protein and consistent pre/post-run timing round this out. Runners who get this baseline right show up to hard sessions with glycogen already topped off, instead of trying to compensate mid-run.
→ Read: Everyday fueling for runners: eat for the runner you are, not race day
Sweat carries sodium along with water, and once a run stretches past about an hour — or the weather turns hot and humid — replacing water alone creates an imbalance rather than solving one. Drinking to thirst without electrolytes can leave a runner diluted, not just dehydrated, which shows up the next day as elevated resting heart rate, low HRV, and heavy-legged easy paces. Hydration needs scale with duration and heat, not a flat daily number.
→ Read: Water alone isn't enough on long runs
Glycogen stores last roughly 90 minutes at running effort. Below that threshold, water is enough and carb intake is largely irrelevant. Cross it, and the clock starts running on finite fuel — pace and effort both suffer once the tank empties, and the deficit compounds through the back half of a run. The practical guidance is duration-based: 30–60 g/hr of carbs for runs between about 75 and 150 minutes, 60–90 g/hr beyond that, starting within the first 30–40 minutes rather than waiting until hunger or fatigue shows up.
→ Read: Mid-run fueling: when carbs start to actually matter
Half marathons sit mostly within glycogen's natural runway, so 30–60 g/hr — starting with a gel at 20–30 minutes and repeating every 30–40 minutes — covers most runners. Marathons are a different problem: the distance reliably outlasts stored glycogen, which is why over 40% of marathoners report hitting the wall around mile 20. The fix is the same principle scaled up — fuel early, target 60–90 g/hr, and use a glucose-fructose blend above 60 g/hr since a single sugar source maxes gut absorption around 60 g/hr. None of this works on race day if it hasn't been rehearsed; gut tolerance for higher carb loads is trained over weeks, not improvised.
→ Read: Half Marathon Fueling: The 30-60g Carb Rule That Actually Works → Read: How Many Carbs Per Hour for a Marathon (and Why It Takes Practice) → Read: Why Marathoners Hit the Wall at Mile 20 (And How to Avoid It)
Topping off glycogen before a marathon or half isn't about one giant pasta dinner — it's a one-to-three-day shift toward roughly 8–12 g/kg of carbohydrate per day while tapering, which brings well-trained runners to maximum glycogen storage without the bloated, heavy-gut feeling that comes from overloading the night before. The bigger risk at this stage is trying something new; race-week fueling should reuse what's already been tested in long runs.
→ Read: Race-week nutrition: carb-loading and what to eat before a race
Despite the 60–90 g/hr target being well established, most marathoners take in only 22–35 g/hr in practice — roughly half of what the research supports. Recent data ties higher carb intake directly to outcome: runners consistently hitting 60–90 g/hr are meaningfully more likely to break 3:00 than those relying on a gel every 45 minutes. The limiting factor isn't leg fitness, it's gut absorption capacity, which is exactly why gut training and a glucose-fructose blend matter as intake climbs.
→ Read: Why Most Marathoners Leave Time on the Table by Under-Fueling
These eight articles form the fueling cluster: daily nutrition and hydration set the foundation, mid-run carb timing and race-distance specifics build on it, and the advanced piece on the intake gap closes the loop by showing what happens when the earlier guidance is ignored.