Marathon Race Day Nutrition Guide

At 30km, your training is done and your decisions are exposed. Not the decision you make at 30km — the ones you made in the 48 hours before the gun, at breakfast, and at kilometre 5 when you chose not to take your first gel because you still felt comfortable.

Marathon race day nutrition isn't a backup system for your fitness. It's part of the race itself. Get it right and your training shows up. Get it wrong and a strong build unravels into a positive split, cramp, dizziness, or the particular kind of misery where your legs are still moving but nothing is responding the way it should.

This guide is built for runners who want numbers, structure and fewer surprises when the effort starts to bite.

"What separates a well-executed marathon from one that falls apart at 32km is almost always fuelling — not fitness. I've seen athletes with extraordinary training do nothing with it on race day because the nutrition plan was vague. The runners who race well to the finish are the ones who treated their carbohydrate and sodium targets the same way they treated their pacing. Non-negotiable. Rehearsed. Automatic."
— Alistair Brownlee, Two-time Olympic Triathlon Champion and founder of truefuels

What matters most on race day

Three variables decide whether nutrition helps or harms your performance: carbohydrate per hour, fluid per hour, and sodium relative to sweat loss. Get all three roughly right and your training has a fair chance to show up. Miss any one of them and the remaining two can't compensate.

Carbohydrate is the priority. Muscle glycogen stores are limited, and the marathon sits squarely in the range where under-fuelling becomes costly. The intestine's carbohydrate absorption capacity can reach 90–120g per hour when you use a 1:1 glucose-to-fructose ratio — the format that activates both SGLT1 and GLUT5 transporters simultaneously. For most trained runners, a practical race target is 60–90g per hour. Start conservative if you haven't tested high-rate fuelling in training.

Fluid is more individual. A broad starting point is 400–800ml per hour, adjusted to body size, pace, weather and your own sweat rate. More is not always better — slow runners in particular can over-drink if they're at every aid station for four to five hours.

Sodium supports fluid balance and improves how effectively your body uses what you drink. It also actively enhances glucose absorption via the SGLT1 co-transporter — which means your carbohydrate fuelling works better when sodium is present. Most marathon runners do well targeting 400–700mg per hour in moderate conditions, with heavier sweaters and hotter races pushing that higher.

The 24–48 hours before the start

Most race day problems begin before the gun. If glycogen stores aren't topped up — or if the final two days become a festival of fibre, heavy food and inconsistent eating — you're asking your legs to solve a problem on the move.

For the final 24–48 hours, shift meals towards carbohydrate and reduce GI risk. Lower fibre, lower fat, consistent portions across the day. White rice, pasta, potatoes, bread, oats, bananas and simple snacks are reliably better choices than anything heavy, unusual or hard to digest. Drink consistently and include sodium — particularly if you're travelling, in warm conditions, or if you tend to wake up slightly dehydrated.

The evening meal should feel ordinary. Enough to feel stocked. Not so much that sleep suffers or you're still digesting at 6am.

Race morning breakfast

Aim to eat 2.5–4 hours before the start.

Keep protein and fat moderate. If coffee is part of your normal routine and it works for you, race day is not the day to stop. If you don't know how you respond to race-morning caffeine, you found that out in training — not now.

During the race: build a fuelling rhythm early

The most consistent mistake in marathon nutrition is starting too late. Waiting until 90 minutes because you still feel comfortable means by the time energy dips, your options are narrower. Carbohydrate takes 15–20 minutes to fully enter the bloodstream. You're fuelling for 30 minutes from now, not for right now.

Take your first gel within 20–30 minutes of the start. Then establish a schedule and stay on it.

Carbohydrate targets by finish time

At 40g per truefuels gel and a 1:1 glucose-to-fructose ratio, 2 gels per hour delivers 80g — in the performance range for most runners, with both intestinal transporters active simultaneously. The gel's fluid texture means it's easy to take at high breathing rates and can be mixed into water if preferred — particularly useful later in the race when swallowing becomes less comfortable.

Gel variant selection by conditions:
- Cool race (under 15°C): 40/0.25 gels — 98mg sodium per gel
- Warm race (15–22°C): mix of 40/0.25 and 40/1.0 — adjust ratio to your sweat rate
- Hot race (above 22°C) or heavy sweater: 40/1.0 gels — 386mg sodium per gel, plus consider the Active Hydration sachet at aid stations

Hydration and sodium in real conditions

A marathon at 8°C and overcast is a different race from one at 18°C in bright sun. Your hydration plan should reflect that, not be copied from another runner's training diary.

The most practical way to know your needs is sweat rate testing in training. Weigh yourself before and after a 60-minute steady run in similar conditions, note what you drank, and calculate hourly sweat loss. You don't need a lab. You need one data point per set of conditions.

Sodium needs by runner profile

If you finish long runs with visible white salt lines on your kit, or if you've cramped or faded badly in warm-weather training, sodium deserves more attention in your plan — not just on the day, but in the weeks before through training rehearsal.

Avoiding GI problems

Most marathon stomach issues are predictable. They come from: taking fuel too late and then overcorrecting, mixing unfamiliar products, under-drinking with concentrated carbohydrate, over-drinking plain water without enough sodium, or running harder than the gut can tolerate.

The truefuels gel is unflavoured and contains no artificial sweeteners, preservatives or emulsifiers — which addresses the three most common causes of GI distress at race intensity: osmotic overload from sweeteners, delayed gastric emptying from thick texture, and flavour fatigue that makes consumption harder over three or four hours.

Practise fuelling at target race pace, not only on easy long runs. Effort changes gut tolerance. A product that's fine at 6:00/km may be borderline at 4:30/km.

A practical race day protocol

Eat a familiar, carbohydrate-led breakfast 2.5–4 hours before the start. Take a small carbohydrate top-up in the final 15 minutes. Begin fuelling in the first 30 minutes and hit a steady hourly carbohydrate target you've already tested. Match fluid to conditions and sweat rate. Include enough sodium to support absorption and replace what you lose — either through the gel's built-in electrolytes, an Active Hydration sachet at aid stations, or both.

If you miss one feed, resume the plan calmly at the next opportunity. Don't double up. The aim is control, not rescue.

The best race day nutrition isn't clever. It's repeatable. If your plan is simple enough to execute at 35km — when your brain is working harder than you'd like — it's strong enough to support the race you trained for.