Marathon Fueling Strategy: Water and Gels
Proper hydration and fueling are as important as your training plan on race day. In a 4-hour marathon, your body can burn 2,500–3,500 calories and lose 2–4 liters of sweat. Without adequate replenishment, pace will drop significantly in the final miles — the notorious "hitting the wall."
The general hydration guideline is to drink to thirst, with approximately 400–600 ml (14–20 oz) per hour for most conditions. Hotter races increase sweat rate and require more frequent intake. For energy, take your first gel around 45 minutes in, then every 35–45 minutes thereafter. Always chase gels with water (not a sports drink) to prevent gastric distress.
Practice your fueling plan during long training runs to identify any GI sensitivities before race day. Never try a new gel brand or flavor during the race itself.
Frequently Asked Questions
Drink to thirst — roughly 400–800 ml (14–27 oz) per hour. Over-drinking is dangerous (hyponatremia) so avoid forced drinking beyond thirst cues.
Start the first gel at 45 minutes, then every 35–45 minutes. Always take gels with water, not a sports drink.
For races under 2 hours, possibly. For a full marathon, especially for slower runners (3h+), energy gels help prevent glycogen depletion in the final miles.