What to eat, drink, and time around runs so your engine has fuel when it needs it.
Running performance lives and dies in the kitchen long before it plays out on the road. This pillar covers the full arc of runner fueling: how to eat day-to-day so training actually sticks, when water stops being enough, how to top off glycogen before a race, and how much carbohydrate you actually need moving on race day—plus why most runners are quietly leaving time on the table by taking in far too little.
Most runners spend energy worrying about what to eat on race morning and underestimate the cumulative effect of six ordinary days of eating in between. Carbohydrate is the primary fuel for running, and muscle glycogen—your stored form of that fuel—has to be consistently replenished or easy runs drift hard, recovery drags, and training quality erodes. For runners logging roughly an hour a day, that means about 5–7 grams of carbohydrate per kilogram of body weight daily. Add hours and intensity and the target climbs to 6–10 g/kg. Protein matters too: distributed steadily through the day (rather than front-loaded at dinner), it keeps muscle repair from falling behind the training stimulus.
Timing around runs also counts. Getting carbohydrate and protein in the post-run window—roughly 30–60 minutes after finishing—is a practical habit that's easy to under-prioritize. The goal isn't perfection; it's arriving at each run with the tank already filled rather than scrambling to compensate.
→ Read: Everyday fueling for runners: eat for the runner you are, not race day
For short, cool runs, plain water handles hydration adequately. The math changes above roughly 60 minutes of continuous effort, or any time temperature and humidity are elevated. Sweat isn't pure water—it carries sodium at meaningful concentrations, plus smaller amounts of potassium, magnesium, and calcium. Replace the volume without replacing the electrolytes and two problems emerge: plasma sodium drops, and the sensation of thirst diminishes even though you're still losing fluid. That combination makes it easy to drink too little of the wrong thing at exactly the wrong time.
Sodium is the critical variable. It drives the thirst signal, supports fluid absorption in the gut, and limits the risk of hyponatremia on very long efforts—a real and underappreciated danger when runners drink large volumes of plain water without eating. Electrolyte needs scale with duration and weather, not a fixed daily number.
→ Read: Water alone isn't enough on long runs
A trained runner stores roughly 90 minutes' worth of glycogen at moderate-to-hard effort. Under 75–90 minutes, endogenous stores carry the work and water is genuinely enough. Beyond that threshold, the tank starts running dry. The consequences aren't immediately catastrophic—they're cumulative: pace slips in the final third, heart rate drifts upward at the same effort, and recovery takes longer than it should.
The practical prescription is simple: start fueling by 30–40 minutes into any run over 75 minutes, before you feel the need. For efforts between 75 and 150 minutes, 30–60 grams of carbohydrate per hour is a reasonable target. For runs exceeding 150 minutes, 60–90 g/hr applies. Late-run pace drop-off and HR decoupling that repeat across long runs are a fueling pattern, not a fitness problem—and treating them as the latter is one of the most common training mistakes recreational runners make.
→ Read: Mid-run fueling: when carbs start to actually matter
Carb-loading has a reputation for excess—a single enormous pasta dinner eaten until discomfort sets in. The actual evidence points to something more measured: a deliberate shift to roughly 8–12 g/kg of carbohydrate per day for the two to three days before a goal race, combined with reduced training volume. That protocol reliably fills glycogen stores to capacity. The single-night approach mostly delivers a heavy gut rather than meaningful extra fuel.
Race morning calls for a familiar, practiced meal—enough carbohydrate to top off liver glycogen after the overnight fast, low in fiber and fat to minimize GI risk, eaten at least two to three hours before the gun. The "nothing new on race day" principle extends to food: a race is not the moment to experiment with unfamiliar fueling strategies, quantities, or products.
→ Read: Race-week nutrition: carb-loading and what to eat before a race
For a marathon, current sports-nutrition consensus places the carbohydrate intake target at 60–90 grams per hour for recreational runners. Elite athletes sometimes push to 90–120 g/hr, but they've spent months conditioning their gut to absorb that volume. Above roughly 60 g/hr, a glucose-only strategy hits a physiological ceiling: the transporter that moves glucose from the gut into the bloodstream saturates at around 60 g/hr. To absorb more, you need fructose alongside glucose, because fructose uses a separate transporter. A glucose-to-fructose ratio of approximately 2:1 is what most sports-nutrition products formulated for high-volume fueling are built around.
The gut is trainable. Taking in carbohydrate on long training runs—not just on race day—teaches the intestine to absorb higher volumes with less distress. Runners who skip in-training fueling and then try to hit 80 g/hr on race day are essentially asking an untrained system to handle a maximal load. GI problems that feel like bad luck are often the predictable result.
→ Read: How Many Carbs Per Hour for a Marathon (and Why It Takes Practice)
The average recreational marathoner takes in somewhere between 22 and 35 grams of carbohydrate per hour during a race—roughly a single gel every 45 minutes. Research published in 2025 puts the gap in stark terms: runners consistently hitting 60–90 g/hr are substantially more likely to break three hours than those working from the typical low-intake strategy. That's not a marginal difference. It's a gap wide enough to reshape finish-time projections across the field.
The implication is practical: if pace fades after mile 16–18 with heart rate climbing, the first variable to interrogate is carbohydrate intake per hour, not fitness, not taper, not course conditions. For most recreational marathoners, doubling or tripling current on-course intake—done gradually, with gut-training weeks built into the training block—is the highest-leverage fueling intervention available.
→ Read: Why Most Marathoners Leave Time on the Table by Under-Fueling
The articles in this cluster move from the foundation (daily eating and hydration) through race-day execution (loading, on-course intake, gut training) and connect directly to how RunNerd interprets training signals—pace drift, HR decoupling, elevated resting heart rate—as potential fueling flags rather than fitness problems alone.