Why fuelling decides long races
Your muscles and liver store only a limited amount of carbohydrate as glycogen — typically enough for somewhere around 90 to 120 minutes of hard running. In a marathon, the runners who “hit the wall” around 30–35 km are usually the ones who ran out of carbohydrate. Taking in carbohydrate during the race spares your remaining glycogen and keeps blood sugar steady, so you can hold pace to the finish.
How much carbohydrate per hour?
Current sports-nutrition guidance, including the 2016 joint position statement of the American College of Sports Medicine, the Academy of Nutrition and Dietetics and Dietitians of Canada, recommends intakes that scale with event duration:
| Event duration | Carbohydrate during exercise | Notes |
|---|---|---|
| Under ~45 minutes | Not needed | Glycogen stores are sufficient. |
| 45–75 minutes | Small amounts or mouth rinse | Even rinsing with a sports drink can help performance. |
| 1–2.5 hours | 30–60 g per hour | Most half marathons and fast marathons. |
| Over 2.5 hours | Up to 90 g per hour | Use glucose + fructose products; requires gut training. |
How many gels for a marathon?
The table shows total carbohydrate and the number of 25 g gels needed for common marathon times, assuming no carbohydrate from sports drinks.
| Finish time | At 45 g/h | At 60 g/h | At 75 g/h |
|---|---|---|---|
| 3:00:00 | 135 g · 6 gels | 180 g · 8 gels | 225 g · 9 gels |
| 3:30:00 | 158 g · 7 gels | 210 g · 9 gels | 262 g · 11 gels |
| 4:00:00 | 180 g · 8 gels | 240 g · 10 gels | 300 g · 12 gels |
| 4:30:00 | 202 g · 9 gels | 270 g · 11 gels | 338 g · 14 gels |
| 5:00:00 | 225 g · 9 gels | 300 g · 12 gels | 375 g · 15 gels |
| 5:30:00 | 248 g · 10 gels | 330 g · 14 gels | 412 g · 17 gels |
| 6:00:00 | 270 g · 11 gels | 360 g · 15 gels | 450 g · 18 gels |
In practice, most runners take their first gel around 30–45 minutes in and then one every 25–40 minutes, and they do not need one in the final 20–30 minutes.
Carb-loading and the pre-race meal
- Carb loading: for races longer than about 90 minutes, aim for 10–12 g of carbohydrate per kg of body weight per day for the 36–48 hours before the start, while tapering your training. Rice, pasta, bread, potatoes, cereals, juice and sweets all help; keep fibre and fat low.
- Race-morning meal: 1–4 g/kg of carbohydrate eaten 1–4 hours before the start — the closer to the start, the smaller the meal.
- Top-up: a gel or sports drink 10–15 minutes before the start can help, especially if your breakfast was early.
Train your gut. Your gut adapts to absorbing carbohydrate during exercise. Practise your exact race products and timing in long runs over several weeks, building up gradually. Nothing new on race day.
Choosing products
Gels
Typically 20–30 g of carbohydrate each. Some are isotonic and need no water; most should be taken with a few sips.
Sports drinks
Commonly around 6 g of carbohydrate per 100 ml, plus sodium. Useful for both fuel and fluid.
Chews & bars
Easier to split into small doses; bars are better suited to slower paces and ultras.
Glucose + fructose
Products combining both sugars allow higher absorption rates — needed for intakes above about 60 g/h.
Fluid needs are individual: measure yours with the sweat rate calculator. Then line up gels with your splits using the marathon pace calculator or print them on a pace band.
- Thomas DT, Erdman KA, Burke LM (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Acad Nutr Diet 116(3):501–528.
- Jeukendrup A (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Med 44(Suppl 1):S25–S33.
Last reviewed: September 2026 · Health disclaimer