Energy intake during runs can be crucial, especially for longer distances. Much has been written and researched on the topic. How far should I run before taking carbs? How much should I take? How often? In what form should they be? Will it upset my stomach?
Questions pile up.
Most agree that it's best to consume carbs when running long.
Opinions vary, but many believe that consuming carbs is key to avoiding hitting the wall during marathons. However, too many carbs too quickly can upset your stomach, requiring a bathroom break, which is undesirable during a marathon.
Why do we need carbs at all?
When running, we burn both fat and carbs to fuel muscles. Faster running increases carb burning. Hence, having carbs available helps us perform at our best.
The body converts carbs to glucose, storing it in muscles and liver. Most can store about 500-600 grams in glycogen reserves. We also have blood glucose—our blood sugar—which changes faster than glycogen stores.
We could delve deeper, but I'll move to the questions I posed earlier.
How far should I run before taking carbs? And how much should I take?
We're all different, with varying carb tolerance and burn rates. However, general guidelines are useful for most:
- Activities under 45 minutes: No need for carbs
- 45-75 minutes: Some water and a bit of carbs (1 gel, etc.)
- 1-2 hours: 30g carbs per hour.
- 2-3 hours: 60g carbs per hour.
- Over 3 hours: 90g carbs per hour.
Swedish energy producer Maurten, sponsor of top runners and cyclists like Eliud Kipchoge, used Maurten for both his official and unofficial marathon records, and Jonas Vingegaard's Jumbo Visma team in Tour de France, offers less conservative energy intake recommendations.
Maurten recommends:
- Under 1 hour run: 40g carbs shortly before start
- 1-2 hours: 80g total. 40g shortly before and 40g during
- Over 2 hours: 80g carbs per hour.
(For xx grams per hour, spread intake to avoid stomach issues).
No full consensus on intake amount exists. Test products in training to see what your stomach can handle and how much you need. If aiming for high carb intake during a run, like Maurten suggests, ensure intake comprises isomaltulose or a 2:1 glucose to fructose ratio (e.g., Maurten or High-5 Slow Release). Research shows this form is more stomach-friendly. For standard recommendations, the mix ratio is less critical.
If running in warmer than optimal conditions (16-18°C), consider reducing carb intake. Heat makes carb absorption harder, risking stomach issues if maintaining normal intake for optimal weather.
Despite cautions, it's clear that carb intake during activity is crucial. A 2019 Brazilian study Cycling time trial performance is improved by carbohydrate ingestion during exercise regardless of a fed or fasted state - PubMed (nih.gov) tested if breakfast before activity (105 min cycling at high intensity followed by 10 km time trial) or carbs during was more vital. Four groups: fasted with placebo, fasted with carbs, breakfast with placebo, and breakfast with carbs. Best performers were the carb-consuming groups, showing in-exercise carb intake is more important than pre-activity eating. The top group consumed both breakfast and carbs.
The final question: “Will it upset my stomach?” No guarantees—everyone's different—but following general advice, practicing pre-race, and spreading intake should keep you safe. Remember, carbs aid in reaching goals on long distances, but too many too fast can cause issues.
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