You are 40 minutes into your run, everything is going well, and you see another runner pulling a gel from their shorts. Do you need that too? The short answer: probably not for this training session. But as soon as you run longer or more intensely, that changes quickly.
Fueling while running is a skill in itself. Whoever masters it well can perform longer, recovers faster, and avoids that dreaded bonk that every runner who has waited too long has experienced.
Do you need anything at all while walking?
That depends entirely on the duration and intensity of your training.
Up to 60 minutes: Most runners do not require additional nutrition. With a normal diet, your glycogen supply (the stored carbohydrates in muscles and liver) is more than sufficient for an hour of walking, even at moderate intensity. Drinking water can be useful, depending on the temperature.
60 à 75 minutes: at the border. With quiet zone 2 training you can still get away with not eating. With more intense sessions, your glycogen stores start to decrease. A small intake (20 à 30 grams of carbohydrates) can make the difference.
Longer than 75 à 90 minutes: fueling is no longer an option, but a necessity. Anyone who ignores this will encounter glycogen depletion: sudden fatigue, difficulty concentrating, a feeling as if your legs are made of lead. Popularly known as "the man with the hammer" or in English "hitting the wall".
How many carbohydrates do you need while running?
The guideline from sports nutrition organizations such as the American College of Sports Medicine:
- 60 à 90 minutes: 30 grams of carbohydrates per hour
- 90 minutes à 2.5 hours: 60 grams of carbohydrates per hour
- Longer than 2.5 hours: up to 90 grams of carbohydrates per hour (provided your intestines are trained)
That 90 grams per hour is an upper limit that requires intestinal adjustment. Your intestines cannot absorb carbohydrates indefinitely: the transporters that absorb glucose and fructose become saturated. Anyone who never fuels while running and suddenly tries to do so in large quantities during a marathon risks stomach complaints.
"The gut is a trainable organ." — Asker Jeukendrup, sports nutrition scientist and marathon runner, on the importance of training the intestines for competition nutrition.
What are your options?
Energy gels
The most practical option for most runners. Compact, easy to carry, quickly absorbed. One gel typically contains 20 à 25 grams of carbohydrates. Always take them with water: gels are concentrated and absorb moisture from your intestines if you take them dry, which can cause stomach problems.
There are two main types: isotonic gels (can be done without water) and regular gels (always with water). Read the label.
When to take: take your first gel after 45 à 60 minutes, then every 30 à 45 minutes depending on intensity.
Sports drinks
An alternative that combines hydration and energy. An isotonic sports drink usually contains 6 à 8% carbohydrates, which optimizes absorption. Handy for those who have difficulty tolerating gels or who prefer to drink rather than chew.
Disadvantage during competitions: you are dependent on what is offered at the refreshment stations.
Energy bars and gummies
Absorbed less quickly than gels or drinks. Useful at low intensity (walking, leisurely long runs) but less suitable at high intensity where blood goes from your intestines to your muscles. Chewing gummies are a middle ground: faster than a bar, a little slower than a gel.
Plain food
Bananas, dates, raisins, rice balls. A great option for ultra running and long trail runs, but less practical for short races or hard training due to slower digestion. Many ultrarunners swear by real food because it fills the stomach better and lasts longer.
Training the intestines: why you do this in training
One of the most common mistakes among recreational runners running their first marathon or half marathon: they have never practiced eating while running, and try to take a gel for the first time on race day.
Your intestines react differently during exercise than at rest. Blood flow decreases, stomach emptying slows, and tolerance to food decreases. This means that your stomach tolerates less when walking than at home on the couch.
The solution: practice your competition nutrition during training. Take the same gels, at the same time, with the same amount of water as you plan to on race day. Your intestines adapt, and you know what works for you.
Timing and strategy
Start early, take small amounts: don't wait until you're empty. Replenishing glycogen while supplies are still available is more efficient than trying to recover from a deficiency.
Always take gels with water: the combination ensures the correct osmolarity in your intestines and faster absorption.
Never experiment on race day: only use what you have tested. Stomach problems at kilometer 18 of a half marathon are an expensive lesson.
Heat increases demand: at high temperatures, glycogen use accelerates and the risk of stomach problems increases. When it is warm, take a little less at a time, but more often.
Frequently asked questions
Do I have to take gels with me to every workout?
Are cheap private label reps as good as expensive sports gels?
Can I use regular Coke as an energy source while walking?
What if I get stomach problems while walking?
In summary
You do not need extra nutrition for workouts of up to 60 minutes. Above that: 30 à 60 grams of carbohydrates per hour, preferably via gels or sports drinks that you tested during training. Start early, take small amounts, and always drink water with gels.
→ What do you eat before a workout to start well prepared? Read nutrition before running.
→ How do you recover as quickly as possible after a long or intensive session? Read nutrition after running.
Bart Vandenbussche is passionate about sport and never shies away from a sporting challenge. He has run several marathons (including sub-3h), is an Iron+Ultra Viking, and currently has the Hyrox bug.
Question or suggestion?
Do you have a question or suggestion? Let us know!
