Marathon Carb Loading: The Complete UK Guide (Race Week Eating, 2026)

You have done the training. The long runs are in the bank. Race day is six days away. Now comes the part most runners get wrong: race week eating. Carb loading sounds simple, but the version most people do (one huge pasta dinner the night before) is not what the research says works.

The biggest mistake we see at Edge is not over-eating. It is under-eating. Most marathoners hit maybe 4-5g of carbs per kg of body weight during race week, when the protocol calls for 8-12g per kg. They then eat a giant heavy meal at 8pm the night before the race, sleep poorly on a full stomach, and toe the line under-fuelled and bloated.

This guide fixes that. We will walk through what carb loading actually is, why it works, the exact three-day protocol with grams per kilo, what to eat, what to avoid, race morning breakfast, and the six most common mistakes. There is also a calculator so you can plug in your body weight and get your daily carb target.

One honest note up front. Edge builds your training plan. Edge does not build nutrition guidance into every plan. You can ask Edge AI questions about your taper week or talk to a real coach for a personalised plan, but the food protocol below is yours to follow. Read carefully. This is the part of marathon prep that wins or loses races.

What carb loading actually is

Carb loading is a strategic increase of carbohydrate intake during the two to three days before a marathon, with the goal of maximising the amount of glycogen stored in your muscles and liver. Glycogen is the fuel your body burns hardest during endurance running. The more you have on board at the start, the further you can run before energy systems start to fail.

The idea has been around since the 1960s. The original protocol was a seven-day plan that started with a hard depletion run plus a low-carb phase to "trick" the muscles into storing more carbs later. It worked, but it was miserable. Runners felt flat and ill during the depletion phase, often peaked too early, and frequently got sick before race day.

Modern sports nutrition research has simplified the whole thing. We now know that a well-trained runner does not need the depletion phase at all. One to three days of high carbohydrate intake (8-12g per kg per day) combined with reduced training volume during the taper is enough to fully top up glycogen stores. The protocol is simpler, kinder, and just as effective.

Why carb loading works

Your muscles store carbohydrate in a form called glycogen. A typical trained runner walks around with around 400g of glycogen on board, spread between muscles and liver. After a proper carb load, that number can climb to 600-800g. That is the entire reason this protocol exists. More fuel in the tank means more miles before the tank runs dry.

The maths is straightforward. At marathon pace you burn roughly 100 calories per mile, which is roughly 25g of carbs per mile if you are fuelling on a mostly carb-burning effort. Over 26.2 miles that is around 650g of carbs needed. Even with race-day gels and drinks, an under-loaded runner will hit the wall somewhere between mile 18 and mile 22. That moment when your legs turn to concrete and your brain fogs over is glycogen depletion, not weakness.

A well-executed carb load pushes that wall back, sometimes past the finish line entirely. It will not give you free speed, but it will let you hold your trained pace deeper into the race. For a four-hour marathoner that can be the difference between a steady 9:09 per mile to the finish and a soul-destroying 12-minute mile death march from mile 20 onwards.

The 3-day carb load protocol

Here is the protocol broken down by day. Note that "carbs per kg" means total carbs per kilogram of body weight. A 70kg runner aiming for 10g/kg eats 700g of carbs that day. That is a lot. Spread it across every meal and snack.

Day 3 before race

Today you start ramping carbs and stripping out fibre. Swap wholegrain bread for white. Swap brown rice for white. Drop raw salads and big servings of leafy veg. You can still eat balanced meals, just shift the carb portion higher and the fibre portion lower. Hit 8-10g/kg of body weight. Keep protein normal. Reduce fat slightly. Start hydrating deliberately, including an electrolyte drink with one meal.

Day 2 before race

This is the peak day. You want to push carbs to 10-12g/kg. Add carb-heavy snacks between meals: bagels, bananas, jam sandwiches on white bread, pretzels, a sports drink mid-afternoon. Keep fibre low. Salt-rich snacks help your body hold onto fluid. Continue hydrating. You may feel slightly bloated and that is normal. Glycogen binds water (3g of water per 1g of glycogen) so you are storing fuel and fluid together.

Day 1 before race (race eve)

The big meal goes at LUNCH, not dinner. Pasta with simple tomato sauce and a little chicken. Rice with grilled fish. Jacket potato with beans (only if you are used to them). Eat until comfortably full, not stuffed. By dinner, switch to something small and easy: a bowl of rice with chicken, or pasta with olive oil and parmesan. Bed by 9pm. No alcohol. The 14-16 hour gap between your big meal and the race start means your gut is empty and ready to work.

Best carb sources for race week

Race week is the wrong time for nutritional virtue. The fibre that helps you in normal life is a problem when you are trying to load glycogen without bloating or risking GI distress on race day. Go white. Go simple. Go boring.

• White pasta (75g cooked = 30g carbs)
• White rice (1 cup cooked = 45g carbs)
• White bread (1 slice = 15g carbs)
• Bagel (1 medium = 50g carbs)
• Sports drink (500ml = 30g carbs)
• Banana (1 medium = 27g carbs)
• Maple syrup or honey (1 tbsp = 17g carbs)
• Pretzels (1 oz / 28g = 22g carbs)
• Jacket or boiled potato (1 medium = 35g carbs)
• Jam or marmalade (1 tbsp = 13g carbs)

The reason for white grains specifically is fibre content. Wholegrain bread, brown rice, and oats are excellent in normal weeks. In race week they slow gastric emptying, sit in your gut overnight, and dramatically raise the risk of an unscheduled toilet stop somewhere around mile 6. White grains digest faster, store as glycogen efficiently, and leave your gut empty on race morning.

What NOT to eat in race week

1. Big new fibre-rich foods. Lentils, beans, raw vegetable platters, big salads. Save them for the week after the race.
2. Spicy or fatty restaurant meals. A curry on the Thursday night before a Sunday race is gambling with your race. Cook at home with foods you know.
3. Alcohol. It dehydrates you, depletes glycogen, disrupts sleep, and lowers race-day performance. Save the pint for after the finish line.
4. New protein sources. Race week is not the time to try a new protein shake, a new cut of meat, or a new vegan recipe. Stick to foods your gut has trained on.
5. Heavy late dinner the night before. The classic mistake. A huge pasta meal at 8pm leaves you bloated, restless, and full at 7am on race morning. Eat the big meal at lunch, dinner stays small.

Race morning breakfast

Eat 3-4 hours before the start gun. For a 9am London Marathon start that means breakfast at 5-6am. Yes, it is early. Set an alarm. The goal is 1-2g of carbs per kg of body weight (so 70-140g of carbs for a 70kg runner). The food must be something you have eaten before a long run during training. Race day is not for experiments.

Proven options: porridge with honey and a sliced banana. Two slices of white toast with honey and a smear of jam. A bagel with jam. A bowl of cornflakes with milk and sugar. A few energy bars you have used during long runs. Coffee is fine if you drink coffee normally. If you do not drink coffee, do not start on race morning. Pair the food with steady sipping of water or a sports drink, around 500ml across the morning.

Avoid: anything new. Big fatty breakfasts (no full English). High-fibre cereals. Cold milk if your gut is sensitive to dairy. Anything you would not eat before a normal Sunday long run. The point of race morning breakfast is not to fuel the race (the carb load did that) but to top up the liver glycogen that you used overnight. Keep it light, familiar, and finished by 90 minutes before the start.

Common carb-loading mistakes

1. Eating too LITTLE. The most common mistake. Most runners eat their normal amount of carbs and call it carb loading. Aim for the high end of 8-12g/kg. It feels like a lot. That is the point.
2. One giant dinner instead of spread-out meals. Your gut cannot process 600g of carbs in one sitting. Spread the load across breakfast, lunch, dinner, and three snacks.
3. Trying new foods race week. A new gel, a new energy bar, a new pasta sauce. Race week is for foods your gut has rehearsed. New food is risk.
4. Eating high fibre. The biggest hidden cause of race-day GI distress. Drop wholegrains, raw veg, and beans for three days before the race.
5. Not reducing fat. Fat slows gastric emptying. A creamy pasta sauce or a cheese-loaded pizza will sit in your gut for hours. Keep fat low and let carbs move through.
6. Drinking only water. Carb loading pulls water into muscles, but you also need sodium and potassium. Use sports drinks or add electrolyte tabs to your water during race week.

How Edge fits race week

Honest answer: the Edge plan handles your training. Your carb load is your job to execute. Edge does not push nutrition reminders or build hydration timing into every plan. That is what guides like this one are for.

What Edge does do during race week is taper your training intelligently. The plan automatically drops mileage and intensity so your legs arrive fresh. Flexi Swap lets you move sessions if work or family schedules shift. The strength and mobility sessions ease off. And if you have questions during the taper ("should I do this final long run easier?" or "I feel a niggle, what now?") you can ask Edge AI in the app and get an answer in around 30 seconds.

For runners who want a real human in the loop, Edge AI also lets you speak to a coach. A coach can give you personalised nutrition advice, race-pace guidance, and pre-race tactics that no app can match. Edge has more than 17,000 UK members and a free 7-day trial. Monthly is £19.99, annual is £119.99. Making fitness feel good for everyone.