A marathon is long enough to empty your glycogen stores but short enough that most runners underestimate how much fueling they need. The standard advice — “take a gel every 45 minutes” — is a rough approximation that ignores body weight, pace, sweat rate, and individual gut tolerance. The result: most recreational runners hit the wall somewhere between mile 18 and 22. The wall is not inevitable. It is a product of inadequate fueling and poor pacing.

Carbohydrate targets by finish time

Muscle glycogen provides roughly 70–80% of energy at marathon pace. Target these hourly carbohydrate intake rates during the race:

  • Under 3:00 — 60–75 g carbohydrate per hour
  • 3:00–3:30 — 60–75 g/hour
  • 3:30–4:00 — 55–70 g/hour
  • 4:00–4:30 — 50–65 g/hour
  • 4:30–5:00 — 45–60 g/hour
  • Over 5:00 — 45–55 g/hour

Most recreational runners take in 20–30 g/hour. The gap explains why miles 18–22 feel like running through wet concrete.

When to start fueling: the most misunderstood rule

Start eating before you are hungry. Start drinking before you are thirsty. Gels take 10–15 minutes to reach your bloodstream as usable glucose. If you feel energy fading at mile 17, taking a gel then means you will not feel the benefit until mile 18.5–19. You have already slowed. Take your first gel at mile 5–6 (approximately 40–45 minutes in), before you feel any need for it. Every gel after that at 20–25 minute intervals.

Complete race day nutrition schedule

3 hours before the start

Eat your pre-race breakfast. Target 1–2 g of carbohydrate per kilogram of body weight. For a 70 kg runner: 70–140 g carbohydrate. White toast, banana, sports drink, porridge. Avoid high-fiber foods, high-fat items, and anything unfamiliar.

15 minutes before the start

Optional: one gel (caffeinated if you use caffeine) 10–15 minutes before the gun. Most useful if you ate breakfast 3+ hours ago.

Miles 5–6 (40–50 minutes in)

First in-race gel. Non-negotiable for any race longer than 1:45. Take it just before an aid station so you can chase it with water.

Miles 9–10 (75–90 minutes in)

Second gel or equivalent carbohydrate. If the gel is not going down well, switch to sports drink — 200–300 ml per station delivers 14–21 g in liquid form that is easier to tolerate when your gut tightens at race pace.

Miles 13–14 (around 1:45–2:10)

Third fueling. This is a good time for a caffeinated gel if you have not used caffeine yet — caffeine peaks around miles 17–20 when the race gets hard.

Miles 17–18 (approximately 2:20–2:50)

Fourth fueling and the most critical. Miles 18–22 is where the wall appears for underfueled runners. Switch to liquid carbohydrate (flat cola, sports drink) if gels are no longer palatable.

Miles 21–22 (approximately 3:00–3:30)

Final fueling for most runners. One more gel or cola. You have 30–45 minutes left. Getting carbohydrate in here sustains pace through the finish.

Hydration strategy for a marathon

Drink to thirst, not on a fixed schedule. Research consistently shows thirst is a reliable guide to hydration needs in events under 6 hours. Practical aid station strategy:

  • Take a drink at every aid station in the first half, even if just 100 ml
  • In the second half, drink as thirst dictates — usually 200–300 ml every 3–5 km in moderate conditions
  • In heat above 25°C, take 200 ml at every station and pour additional water on your head
  • Sports drink beats plain water when you are also taking gels — it adds carbohydrate and sodium without extra digestive load

Caffeine timing for a marathon

Caffeine consistently improves marathon performance by 2–4%. The mechanism is central nervous system stimulation — it reduces perceived effort so the same pace feels easier. Best timing:

  • One caffeinated gel 10–15 minutes before the start (peaks during miles 4–8)
  • One caffeinated gel at miles 13–15 (peaks during miles 17–20 — exactly when the race gets hard)

Managing GI distress mid-race

If nausea develops, stop taking gels and switch to diluted sports drink. Flat cola (200 ml sips) is often tolerated when nothing else is. Slowing the pace by 10–15 seconds per km for 2–3 km frequently allows the gut to settle enough to resume normal fueling. The most common cause: going out too fast reduces gut blood flow dramatically.

The night before a marathon

Eat a moderate, familiar dinner 3–4 hours before you plan to sleep. White pasta with a simple sauce, white rice and chicken, or similar low-fiber, low-fat carbohydrate sources. Avoid anything you have not eaten before. Eat earlier rather than later — a meal at 7 pm for a 7 am start is better than a meal at 9 pm.

Build your personalized marathon nutrition plan

The right numbers depend on your exact finish time, body weight, sweat rate, and gut tolerance. Generic gel schedules leave too much margin for error. Build your personalized marathon fueling plan — input your race details and it generates a minute-by-minute schedule with specific gel timings, carb targets, fluid volumes, and sodium amounts, delivered as a printable PDF you can carry on race day.

Frequently asked questions

How many gels should I take during a marathon?

Between 4 and 7, depending on finish time and how much sports drink you consume from aid stations. A 3:30 runner targeting 70 g/hour for 3.5 hours needs roughly 245 g total carbohydrate — approximately 5–6 gels plus sports drink from aid stations.

Can I just use sports drink from aid stations without gels?

200 ml of 6% isotonic sports drink delivers 12 g of carbohydrate. If there is a station every mile and you take 200 ml each time, that is roughly 24–30 g per hour — well below the 60–70 g/hour target for most runners. You need gels or additional carbohydrate to supplement aid station drinks.

What happens if I take a gel without water?

The concentrated carbohydrate pulls water from your intestinal wall to dilute it before absorption — potentially causing cramping and diarrhea. Always chase standard gels with 100–150 ml of water. Isotonic gels are formulated to not require water but are more expensive and bulkier to carry.

Is it true running burns fat so I don't need to fuel?

Fat is burned at all intensities, but at marathon pace (typically 75–85% of VO2max), glycogen is the dominant fuel. Fat metabolism alone cannot sustain marathon pace. This is the biochemical reason for the wall — not a lack of fat, but glycogen depletion at the very intensity required to race.

Should I eat race morning even with a nervous stomach?

Yes. Liver glycogen depletes 5–8% per hour overnight, so you wake up with lower stores than when you went to sleep. A small, easily-digested breakfast — white toast with honey, a banana, a sports gel — is better than nothing even if nerves limit appetite. Eat at least 90 minutes before the start to allow digestion.

Does the night-before pasta dinner actually matter?

A single pasta dinner does almost nothing for glycogen stores — your muscles can only absorb carbohydrates so fast. What matters is the 48–72 hours before the race. The night-before meal mostly ensures you sleep with a comfortable, non-empty stomach. Keep it moderate, familiar, and early.