How to Fuel a Marathon: Carbs, Gels and Real Food

To fuel a marathon well, you need three things: enough carbohydrate in the day or two before the race, a familiar carb based breakfast on race morning, and a steady intake of around 30 to 60 grams of carbohydrate per hour while you run, more for longer efforts if your gut is trained for it. Get those right and the dreaded wall at kilometre 30 becomes far less likely.

Fuelling is one of the most under practised parts of marathon training. Runners spend months on their legs and then try something new on race day. This guide covers what the evidence supports and how to put it into practice, whether you are running the Cape Town Marathon, Soweto or the road to Two Oceans and Comrades.

Why marathon runners hit the wall

Your muscles store carbohydrate as glycogen, and at marathon effort it is your main fuel. Most people store enough to run somewhere around 90 minutes to two hours at a hard effort. After that, if you have not topped up, the stores run low and your body leans more heavily on fat, which cannot be burned fast enough to sustain the same pace. That sudden, heavy slowing down is what runners call the wall.

Taking in carbohydrate during the race supplies fuel directly and spares some of your stored glycogen, which is why fuelling during the run makes such a measurable difference over 42.2 kilometres.

Carb loading: the two days before

Carb loading means eating more carbohydrate than usual in the 36 to 48 hours before a race lasting more than about 90 minutes, while your training is tapering. Sports nutrition guidelines suggest around 10 to 12 grams of carbohydrate per kilogram of body weight per day during this window. For a 70kg runner that is roughly 700 to 840 grams of carbs a day, which is a lot more than most people realise.

It does not mean one giant pasta dinner the night before. Spread it across the day and lean on easy to digest foods.

• Rice, pasta, potatoes, bread, wraps and breakfast cereals
• Pap, which is an easy, cheap carb source many South African runners already eat. See is pap bad for weight loss for more on it.
• Fruit juice, flavoured milk and sports drinks to add carbs without bulk
• Lower fibre choices (white rather than wholegrain) for the final day, to keep your gut settled
• Smaller portions of fat and protein than usual, simply to leave room for the carbs

Expect to gain a kilogram or so on the scale. Glycogen is stored with water, so this is a sign the loading worked, not fat gain.

Race morning breakfast

Eat a carbohydrate based breakfast roughly two to four hours before the start. Guidelines suggest around 1 to 4 grams of carbohydrate per kilogram of body weight in this window, with the bigger amounts needing more time to digest. For many runners that looks like white toast or a bagel with honey or jam, a banana, oats, or a bowl of cereal, plus water and their normal coffee.

With early South African race starts, that can mean eating at 3am or 4am. If that is unrealistic, a smaller carb snack 60 to 90 minutes before the gun works better than skipping breakfast entirely. Whatever you choose, it should be exactly what you have already eaten before your long training runs.

How much to take in during the race

Current sports nutrition guidance suggests roughly 30 to 60 grams of carbohydrate per hour for efforts of one to two and a half hours, and up to about 90 grams per hour for longer efforts, using products that combine glucose and fructose so the gut can absorb more. Many marathoners finishing in three and a half to five hours do well somewhere between 40 and 70 grams per hour.

• Start early, around 30 to 45 minutes in, rather than waiting until you feel flat
• Take something every 20 to 30 minutes rather than a big dose every hour
• A typical gel contains around 20 to 30 grams of carbohydrate, so check the label of the brand you use
• Take gels with water rather than sports drink, to avoid an overly concentrated hit in your stomach

Gels versus real food

Gels are popular for a reason. They are compact, easy to carry and absorbed quickly. But they are not compulsory, and some runners simply do not tolerate them well. Real food works too, as long as it is mostly simple carbohydrate and low in fat, fibre and protein during the run.

• Baby potatoes boiled in salted water, which also give you some sodium
• Bananas, dates or dried fruit
• Jelly sweets such as jelly babies, popular on South African long runs
• A small jam or honey sandwich on white bread, better suited to slower ultra paces
• Flat Coke, which many runners lean on in the later stages

Check what your race's refreshment stations offer. Many South African races provide more than water and electrolyte sachets, and knowing what will be on the tables helps you plan what to carry. Do not assume a product you have never tried will agree with you on the day.

Fluids and sodium

Carbohydrate and hydration work together. Drink to thirst for most of the race and use the water stations, rather than forcing large volumes. Overdrinking plain water during a long race can dilute blood sodium, which is rare but genuinely dangerous. On hot days, an electrolyte drink or salty foods help replace the sodium you lose in sweat. Our guide to hydration in hot weather covers working out your own sweat rate.

Train your gut like you train your legs

The gut adapts to taking in carbohydrate during exercise. Runners who practise fuelling regularly on long runs tolerate more carbs on race day, with fewer stomach issues. Use your long runs as rehearsals: same breakfast, same gels or foods, same timing as race day. Build up gradually from around 30 grams per hour toward your target over several weeks.

This is one of the things a coach helps plan into your training block, so fuelling is practised rather than improvised. If you would like a marathon plan with fuelling rehearsals built in, see our online run coaching.

After the finish

Once you can stomach it, aim for a mix of carbohydrate and protein to start recovery: a recovery shake, a chicken wrap, a flavoured milk or a proper meal. Protein needs for runners are covered in more detail in how much protein do runners need.

If you have diabetes, a history of disordered eating, or gut problems that are more than the occasional upset, speak to a doctor or registered dietitian before making big changes to how you eat around races.

Frequently asked questions