What to eat, drink, and time around runs so your engine has fuel when it needs it.
Fueling is the part of training plans runners skip past to get to the workouts — and it's usually the reason a good training block doesn't translate to a good race. The science splits cleanly into two timeframes: what you eat day to day to keep your training tank full, and what you eat before, during, and after key efforts to avoid running out of fuel when it counts. Both matter, and most runners only ever think about the second one.
Beginners tend to spend their mental energy on the pre-race meal and ignore the other six days of the week, but daily fueling is what actually builds — or quietly undermines — fitness. Carbohydrate needs scale with training volume: roughly 5–7 g/kg per day at about an hour of running daily, climbing to 6–10 g/kg as volume rises toward one to three hours. Steady protein and sensible before/after-run timing round it out. A runner who's chronically under-fueled day to day will show it in easy runs that feel harder than they should, late-run fatigue, or recovery that doesn't keep pace with training load — signs that look like fitness problems but are really plumbing problems.
→ Read: Everyday fueling for runners: eat for the runner you are, not race day
Sweat carries sodium along with it, plus smaller amounts of potassium, magnesium, and calcium. For short, cool runs this doesn't matter — your body buffers it fine. Past about an hour, or anytime heat and humidity are working against you, replacing water without electrolytes can leave you worse off, not better, because diluting sodium while you're already losing it compounds the problem. Heat adds its own wrinkle: above roughly 75°F, pace becomes an unreliable guide entirely, since your heart is splitting work between muscles and skin. Running by effort (or watching heart-rate drift) instead of chasing a pace number is the more reliable approach on hot days.
→ Read: Water alone isn't enough on long runs · Hot Out? Here's How to Not Overheat on Your Run
A trained runner carries roughly 90 minutes of stored glycogen. Under that window, water is enough — carbs mid-run won't make or break a 45-minute easy run. Past 90 minutes, the math changes: your tank is running toward empty, and pace holds up only as long as fuel keeps coming in. The general target is 30–60 g of carbohydrate per hour for efforts in the 75–150 minute range, rising to 60–90 g/hour beyond that, starting within the first 30–40 minutes rather than waiting to feel depleted. Late-run pace drop-off paired with rising heart rate is the usual signature of having waited too long.
→ Read: Mid-run fueling: when carbs start to actually matter
For a half marathon, 30–60 g/hour of carbs starting at 20–30 minutes in, repeated every 30–40 minutes, covers most runners — glycogen stores topped up beforehand can carry a good chunk of the load over that distance. The marathon is a different problem: current consensus puts the target at 60–90 g/hour, which usually requires a glucose-fructose blend rather than a single sugar source, since the gut's glucose-only absorption caps out around 60 g/hour. Hitting that number isn't automatic — it takes weeks of practiced gut training in long runs before race day, not a plan improvised mid-race.
→ 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) · Why Most Marathoners Leave Time on the Table by Under-Fueling
Over 40% of marathoners report hitting the wall around mile 20 — which lines up almost exactly with when glycogen stores run dry if fueling started late or stayed too light. Pacing compounds it: going out even 5–10% faster than goal pace can burn through glycogen up to 30% faster, because faster paces lean harder on carbohydrate and less on fat. The two fixes are the same ones covered above — start fueling in the first 30–45 minutes, and don't let an aggressive early pace write a check your glycogen can't cash.
→ Read: Why Marathoners Hit the Wall at Mile 20 (And How to Avoid It) · Hitting the Wall Isn't About Fitness — It's Bad Math
The days before a long race matter more than the final meal. Carb-loading is a one-to-three-day shift toward roughly 8–12 g/kg/day of carbohydrate while tapering, not a single giant pasta dinner the night before. Race-morning breakfast follows a simpler formula: 1–4 g/kg of carbohydrate, 2–4 hours before the start, using food already tested in training. Both practices exist to top off glycogen stores without creating gut problems at the start line — and both fail if the food itself is untested on race day.
→ Read: Race-week nutrition: carb-loading and what to eat before a race · The Pre-Race Breakfast Formula That Actually Works
These articles form the fueling cluster of this pillar — from everyday eating and hydration basics through mid-run and race-specific carb strategy to the wall-avoidance math that ties pacing and fueling together.