What to eat, drink, and time around runs so your engine has fuel when it needs it.
Fueling covers what and when to eat around running — from the everyday meals that keep glycogen stores topped up to the gram-per-hour math of race-day carbohydrate. Most runners think about fueling only in terms of gels and race morning, but the research points the other way: daily habits set the ceiling, and race-day fueling only works if it's been rehearsed in training. This pillar walks through both ends, in order of when they matter.
Race-day nutrition gets the attention, but it's a rounding error next to what a runner eats the other six days a week. Carbohydrate intake needs to scale with training volume — roughly 5–7 g/kg of body weight daily for an hour a day of running, climbing to 6–10 g/kg as volume rises toward 1–3 hours a day. Protein needs to stay steady throughout, not just after hard sessions. When easy runs start feeling harder than they should, or recovery lags between back-to-back days, under-fueling is worth ruling out before assuming it's a fitness problem.
→ Read: Everyday fueling for runners: eat for the runner you are, not race day
Sweat carries sodium, potassium, magnesium, and calcium out with the water. For short, cool runs this doesn't matter — normal eating and drinking covers it. Past about an hour of continuous effort, or in heat and humidity, replacing water alone can leave a runner worse off than replacing nothing, because diluted sodium levels blunt thirst and fluid retention right when both are needed. A rough next-day marker — elevated resting heart rate, sluggish easy pace, low HRV after a hot or long run — is often an electrolyte debt rather than a sign of declining fitness.
→ Read: Water alone isn't enough on long runs
A trained runner carries roughly 90 minutes of glycogen. Below that threshold, water is enough — carbs on the run don't add much. Past 90 minutes, the tank starts running dry and pace pays for it, showing up as a slow fade rather than a sudden wall. The practical rule: under 75–90 minutes, water; over that, start fueling by 30–40 minutes in, aiming for 30–60 g/hr on runs up to about 150 minutes and 60–90 g/hr beyond that. Late-run pace drop-off paired with HR drift in the final third is the pattern to watch for — it usually means the carb target needs to move up, not that the long run needs to get shorter.
→ Read: Mid-run fueling: when carbs start to actually matter
The half marathon and marathon call for different math because the distances stress glycogen differently. For a half, 30–60 g/hr works, with the first gel in by 20–30 minutes and repeats every 30–40 minutes after — typically 2–4 gels depending on finish time. For a marathon, the target jumps to 60–90 g/hr, and above 60 g/hr a single sugar source (glucose alone) can't be absorbed fast enough; a glucose-fructose blend is needed because the two sugars use separate gut transporters. Either way, these numbers only work if the gut has practiced absorbing that volume — race day is the wrong place to test a new gel schedule.
→ Read: Half Marathon Fueling: The 30-60g Carb Rule That Actually Works · How Many Carbs Per Hour for a Marathon (and Why It Takes Practice)
Carb-loading isn't one giant pasta dinner — it's a one-to-three-day shift toward roughly 8–12 g/kg of carbohydrate per day while training tapers, which tops off glycogen stores without the bloated, heavy-gut feeling that comes from overcorrecting the night before. The same principle that governs mid-race fueling applies here: nothing new on race morning. Whatever carb amount and food source gets used on race day should already be familiar from long runs.
→ Read: Race-week nutrition: carb-loading and what to eat before a race
Most marathoners take in only 22–35 g/hr during the race — well under the 60–90 g/hr range that recent research associates with hitting time goals like breaking 3:00. The limiter isn't the legs, it's the gut's capacity to absorb glucose, which is why the transporter-blend logic (glucose plus fructose above 60 g/hr) matters more as the target climbs. Pace drift after mile 18 paired with rising HR is a common late-race signature of this gap, and it's usually addressed by raising long-run carb targets in training, not by hoping race day goes differently.
→ Read: Why Most Marathoners Leave Time on the Table by Under-Fueling
These seven articles form the fueling cluster underneath this pillar — each goes deeper into one piece of the picture, from daily eating habits through race-week and race-day carbohydrate targets.