Half Marathon Fuelling Plan: When and What to Eat on Race Day
The half marathon sits in an awkward spot. It is long enough that running on empty will cost you minutes, but short enough that most runners convince themselves they can wing it. Turn up at any Sunday half in the UK and you will see the evidence: a mass of people who trained sensibly for sixteen weeks, then ate a banana at 7am and hoped for the best. Somewhere around 15km, the wheels start to loosen. Not a dramatic bonk, just a quiet fade — cadence drops, form gets sloppy, and the last 6km takes 90 seconds longer than it should have.
The fix is not complicated, but it does need to be deliberate. A good half marathon fuelling plan is really three plans stitched together: what you do in the 48 hours beforehand, what you do on race morning, and what you take on the move. Get all three roughly right and you arrive at the finish still running your goal pace rather than surviving it. Here is how to build one, with actual numbers rather than vague advice about "eating well".
Why 21.1km Sits on the Edge of Your Glycogen Tank
A trained runner stores somewhere in the region of 400–500g of glycogen across the liver and working muscles, which is roughly 1,600–2,000 kcal of readily available carbohydrate. Running burns approximately 1 kcal per kilogram of body weight per kilometre, so a 70kg runner covering 21.1km will get through around 1,480 kcal. On paper, you have enough. In practice, you do not, because that stored glycogen is not all accessible, you started the morning with liver stores partially depleted from overnight fasting, and the harder you run relative to threshold, the more heavily you lean on carbohydrate rather than fat.
This is why the timing question matters more at the half than at almost any other distance. Below 60 minutes of hard running, you genuinely do not need to eat anything. Beyond about 2 hours, everyone accepts they need to fuel. The half sits right in the middle — most club runners finish between 1:30 and 2:15, and that window is exactly where good fuelling separates a strong finish from a grim one.
The 48 Hours Before: Topping Up, Not Carb Loading
Full carbohydrate loading — the old three-day depletion-then-gorge protocol — is overkill for a half. You are not trying to supercompensate; you are simply arriving at the start line with a full tank. Aim for 6–8g of carbohydrate per kilogram of body weight per day for the two days before the race. For a 70kg runner that is 420–560g of carbs daily, which sounds enormous until you break it down: porridge with honey and banana, a large bowl of pasta, a couple of bagels, a few pieces of fruit and a rice-based evening meal will get you most of the way there.
Two practical notes. First, drop your fibre intake in the final 24 hours. Wholemeal everything is excellent nutrition and a poor race-morning decision — white bread, white rice and low-fibre fruit are your friends here. Second, resist the urge to add extra protein or fat "for staying power". Fat slows gastric emptying, and anything sitting in your stomach at kilometre 12 is a liability. Salt your food a little more generously than usual and drink to thirst rather than forcing litres of water, which just dilutes your sodium and sends you looking for a portaloo.
Race Morning: The Three-Hour Countdown
The evidence-based target for a pre-race meal is 1–4g of carbohydrate per kilogram of body weight, eaten 1–4 hours before the gun. The longer the gap, the larger the meal. Most runners land well with around 1.5–2g/kg three hours out — for a 70kg runner, roughly 100–140g of carbs. That is realistically two slices of white toast with jam and honey, a banana, and a sports drink or fruit juice. Simple, boring, tested in training.
If your race starts at 9am and you cannot face eating at 6am, shrink the meal and move it closer: 1g/kg at 90 minutes out works perfectly well for most people. What you should not do is skip it entirely. Overnight, your liver glycogen drops by 50–60%, and liver glycogen is what keeps your blood glucose stable. Running a half on an empty liver is how people end up feeling light-headed at 16km.
Around 45–60 minutes before the start, take on 200–300ml of fluid and, if you use it, your caffeine. The performance-relevant dose is roughly 3mg per kilogram of body weight — about 200mg for a 70kg runner, or one strong coffee plus a small top-up. Caffeine reliably improves endurance performance by 2–4% in the research, but race day is emphatically not the morning to discover you are a fast metaboliser with a nervous stomach. If you have not practised it, skip it.
Building Your In-Race Half Marathon Fuelling Plan
Here is where most people either do nothing or overdo it. For a half marathon, the target is 30–60g of carbohydrate per hour. That is deliberately lower than the 60–90g/hr you would chase in a marathon or a long sportive, because you are running harder, your gut is getting less blood flow, and you simply do not need that much for 90–130 minutes of work.
A practical structure for a sub-2-hour half marathon fuelling plan looks like this:
- Kilometre 5–6: first dose, around 20–25g of carbs. Take it early, before you feel like you need it.
- Kilometre 11–12: second dose, another 20–25g. This is the one that carries you through the closing 8km.
- Kilometre 16–17 (optional): a smaller top-up if you are running beyond about 1:50, or if the day is hot.
- Fluid: 400–600ml per hour in temperate conditions, more if it is warm. Sip at each station rather than gulping.
Take every dose with water, not on its own. Concentrated carbohydrate needs fluid to move out of the stomach and across the gut wall, and this is the single most common cause of race-day stomach trouble. If you are going above 60g/hr for any reason, use a product blending glucose and fructose in roughly a 1:0.8 ratio — the two sugars use separate intestinal transporters, so you absorb more without overwhelming the SGLT1 pathway.
What We Use at FTP Endurance Fuel
We built our pastilles around the problem we kept having ourselves: gels are messy to open mid-stride, easy to drop, and force you to take 25–30g in one hit whether you want it or not. Chewable pastilles let you dose in increments — two or three at a time, spread over a minute, which is far kinder to your gut at half marathon intensity.
For race day we tend to reach for the Mixed Fruit Pastilles. Flavour fatigue is real even over 90 minutes, and having variety in the pocket means you actually take the second dose rather than talking yourself out of it. In the days after a hard half, the Tart Cherry Pastilles earn their place for a different reason — Montmorency cherry is rich in anthocyanins, the polyphenols shown in several controlled trials to reduce markers of oxidative stress and speed the return of strength after damaging running. If you are racing again in a fortnight, that matters.
The one rule that overrides everything above: nothing new on race day. Every element of this plan — the pre-race meal, the timing, the product, the amount — should be rehearsed at least twice in your long runs at race pace. Your gut is trainable, and the runners who never have stomach problems are usually just the ones who practised. Pick your plan, run it in training, and let race morning be the boring part. If you want to trial a fuelling approach before committing, our Taster Pack is a straightforward place to start.
