What is the best fuel strategy for marathon runners?

October 22, 2025 •

4 min read

According to sports dietitians, an average marathon runner can deplete their glycogen stores, the body's primary fuel source, in just 90-120 minutes without proper fueling. Understanding what is the best fuel strategy for marathon training and race day is critical to avoid 'hitting the wall' and maintaining peak performance across the full 26.2 miles.

Quick Summary

A successful marathon fueling strategy involves a multi-day carb-loading phase, a carefully timed high-carb breakfast, and consistent intra-race nutrition. Runners should practice with gels, chews, or sports drinks during training to find what works best, complementing these with a structured hydration plan based on personal sweat rate. Avoiding high-fiber foods and fat close to race time is also essential for preventing gastrointestinal issues.

Key Points

Pre-Race Prep: Start carb-loading 1-2 days before the race with high-carb, low-fiber meals to maximize glycogen stores.
Consistent Fueling: Aim for 60-90 grams of carbohydrates per hour during the race, starting early and consuming fuel in regular, small doses.
Strategic Hydration: Match your fluid intake to your personal sweat rate, supplementing with electrolytes, and practice this strategy in training.
Don't Experiment: Only use fuels and hydration products on race day that you have successfully tested during long training runs.
Balance is Key: Combine a carb-heavy breakfast with small, consistent intakes of gels, chews, or drinks during the race, avoiding high fat and fiber.
Train Your Gut: Practice your fueling and hydration strategy during training runs to acclimate your digestive system to race conditions.
Post-Race Recovery: Consume a carbohydrate and protein rich snack or meal within an hour of finishing to kickstart muscle repair and glycogen replenishment.

The Science of Marathon Fueling

During a marathon, your body relies on two main fuel sources: carbohydrates and fat. Carbohydrates, stored as glycogen in your muscles and liver, provide quick energy for high-intensity efforts, while fat serves as a slower-burning energy reserve for less intense activity. A major goal of a marathon fuel strategy is to conserve your limited glycogen stores by consuming carbohydrates during the race, thereby delaying fatigue and preventing 'the bonk'.

Carb-Loading: The Days Before the Race

Carb-loading is the practice of increasing carbohydrate intake in the days leading up to a race to maximize glycogen stores. The best practice is to start this process 1-2 days before the event, aiming for an intake of 8-12 grams of carbohydrates per kilogram of body weight each day. Simultaneously, reduce your intake of fat, protein, and high-fiber foods to minimize digestive stress and bloating.

Focus on low-fiber, high-GI carbs: Opt for simple carbs that are easy to digest. Good examples include white rice, white bread, pasta, potatoes, and sports drinks.
Don't overeat: The goal is to shift macronutrient ratios, not to gorge on more food overall. Liquid carbs, such as juices or sports drinks, can help you meet targets without feeling overly full.
Hydrate consistently: Continue to hydrate well in the days before the race, supplementing with electrolytes to help your body retain fluid. Aim for pale yellow urine as a hydration indicator.

The Marathon Morning Plan

The morning of the race is about topping off your liver's glycogen stores. Your pre-race meal, ideally consumed 2-4 hours before the start, should be high in carbohydrates but low in fat, protein, and fiber. A light carbohydrate snack can be taken closer to the start line.

During the Race: Regular Fueling is Key

For a marathon, consuming 60-90 grams of carbohydrates per hour is a standard recommendation for most runners, though faster athletes may benefit from higher amounts. Begin fueling early, around 30-45 minutes into the race, and continue with consistent, small intakes every 15-20 minutes.


Fueling Options Comparison	Option	Pros	Cons	Best For	Carbohydrates (per typical serving)
Energy Gels	Quick absorption, easy to carry, concentrated energy.	Can cause GI distress if taken without water, texture may be unappealing.	All-around performance fuel; isotonic gels for better absorption.	20-25g
Energy Chews	Solid food texture, palatable, often have added electrolytes/caffeine.	Requires chewing and digestion, can be sticky.	Runners who prefer solid food texture and slower absorption.	18-25g (per serving)
Sports Drinks	Provides carbs and electrolytes, aids hydration.	Can be bulky to carry, requires drinking consistent volume.	Supplementing carb intake and maintaining hydration.	Variable; check labels
Real Food	Natural ingredients, can be easier on the stomach for some.	Messy to carry, harder to eat while running, slower digestion.	Runners with sensitive stomachs or for lower intensity.	Varies (e.g., banana 27g)

Hydration Strategy and Electrolytes

Adequate hydration is inseparable from a successful fueling strategy. Your specific fluid and electrolyte needs will depend on your individual sweat rate, pace, and weather conditions. A good hydration strategy involves drinking regularly rather than waiting for thirst, which is an unreliable indicator.

Calculate your sweat rate: A simple way to estimate your fluid loss is to weigh yourself before and after a one-hour run under similar conditions to race day. The weight difference (accounting for fluid intake during the run) indicates your sweat rate. For every pound lost, aim to consume 20-24 ounces of fluid post-run.
Replenish electrolytes: Sweat also contains essential electrolytes, particularly sodium, which need to be replaced to prevent cramping and maintain fluid balance. This is especially important for 'salty sweaters'. Sports drinks, chews, or salt capsules can help replenish electrolytes effectively.
Avoid over-hydration: Drinking too much water can lead to a dangerous condition called hyponatremia (low blood sodium). Signs include a sloshing stomach, dizziness, and swelling of the extremities.

The Power of Practice and the Post-Race Plan

One of the biggest mistakes is trying something new on race day. Use your long training runs as a dress rehearsal for your race-day nutrition plan, including your pre-race breakfast, on-course fuel, and hydration. Practice taking gels and drinks at race pace to train your gut to handle the intake under stress. After the race, a recovery shake or meal containing both carbohydrates and protein within 30-60 minutes is crucial for replenishing glycogen stores and repairing muscle tissue.

In conclusion, the best fuel strategy for marathon success is a personalized, practiced plan built on the foundation of smart carb-loading, consistent race-day fueling, and a tailored hydration approach. By treating your nutrition with the same dedication as your training, you can power through the miles feeling strong and confident. For additional expert insights, consult resources from organizations such as the American College of Sports Medicine, which provides in-depth nutritional guidelines for endurance athletes.

Frequently Asked Questions

To avoid hitting the wall, you must consistently replenish your glycogen stores during the race. Start consuming carbohydrates early, about 30-45 minutes in, and continue with a steady intake of 60-90 grams per hour to keep your energy levels stable and delay fatigue.

Eat a familiar, high-carbohydrate, low-fiber, and low-fat breakfast 2-4 hours before the race. Examples include a bagel with jam, oatmeal, or a banana. This meal tops off liver glycogen stores without causing digestive issues.

Fluid intake should be individualized based on sweat rate, but a general guideline is 300-600ml per hour. Drink small amounts consistently every 15-20 minutes, using a sports drink or water combined with electrolytes to replace lost salts.

The best choice depends on personal preference and tolerance. Gels offer a quick, concentrated source of energy, while chews provide a slower release and a more solid texture. Practice with both in training to see what your stomach handles best at race pace.

Begin carb-loading 1-2 days before the race by increasing your carbohydrate proportion to 8-12g/kg of body weight daily while reducing fat and fiber. Focus on easily digestible sources like white rice and pasta, rather than overeating and feeling bloated.

Common causes include dehydration, over-consuming sugar, or trying new foods. Prevent issues by practicing your fueling strategy, hydrating properly, and sticking to low-fiber, low-fat foods before and during the race.

Caffeine is a proven performance enhancer, but dosage and timing are individual. Small doses (1-1.5 mg/kg) in the later stages can provide a boost. Practice with caffeinated gels or drinks in training to assess your tolerance.