August 17, 2023

Fueling Facts: Fueling for Endurance Events: Chicago Marathon

by Rachel Klomstad, MS, RD

In late summer, the streets of Chicago are filled with runners training for the iconic Bank of America Chicago Marathon. From seasoned marathoners racing for a personal record to first timers aiming to finish the race, the Chicago Marathon brings together runners looking to conquer the 26.2-mile challenge. In our previous blog, “How to Prepare for a Marathon”, we leveraged the expertise of Dan Kremske, elite runner and our very own Care Coordinator, to provide us with his insights and best practices in training for marathons. With the race only eight weeks away, training is currently at its peak for most runners. Regardless of a runner’s experience level or speed, a strategic fueling plan can make the difference between a personal record and a failure to finish. In this week’s Fueling Facts, our SHIFT registered dietitians share fueling tips to maximize marathon training and to help you feel your best on race day.


For any marathoner, the primary goals during the training period are to: 1) adjust fueling to adequately support changes in training load, 2) experiment with various race-day meals, snacks, and intra-race fuel to determine the ideal race day fueling plan, and 3) optimize hydration. It is important to account for changes in training intensity, climate, and injuries/illnesses when considering your fueling regimen. Focus on the following tips as you navigate the final 8 weeks of the marathon training period.

1. Fuel Adequately Based on Training Volume

It is important to adjust your Balanced Plate proportions based on the intensity and volume of your training each week (or even each day), while also considering your current nutrition and health goals. Since carbohydrates serve as the primary energy source for your muscles when running, greater amounts of carbohydrates are necessary as intensity and volume of training increases. During exercise, the body accesses energy from glycogen, a form of carbohydrates stored in skeletal muscles and the liver. Shown in the graph below, glycogen stores are eventually depleted in longer endurance events (e.g., half-marathons and marathons), which is why ‘topping off’ glycogen stores (via adequate carbohydrate intake) is important throughout training and around race day.

Source: Rapoport BI (2010) Metabolic Factors Limiting Performance in Marathon Runners. PLoS Comput Biol 6(10): e1000960.

Based off the US Olympic Committee’s ‘Athlete Plates’, we recommend the following Balanced Plate adjustments for light, moderate, and hard training days.

  • Light Training Day (rest day or active recovery): Maintain the standard Balanced Plate proportions for lunch and dinner meals: ½ non-starchy vegetables, ¼ lean protein, and ¼ complex carbohydrates.
  • Moderate Training Day (less than 60 minutes of moderate to intense training): Increase your complex carbohydrate intake slightly for lunch and dinner meals. Make your lean protein ¼ of the plate and split the remainder of the plate between non-starchy vegetables and complex carbohydrates.
  • Intense Training Day (greater than 60 minutes of moderate to intense training): Increase your carbohydrates for lunch and dinner meals, aiming for: ¼ non-starchy vegetables, ¼ lean protein, and ½ complex carbohydrates.

2. Practice Race Day Fueling

The training period is also an ideal time to practice your race day fueling regimen, including your pre-race, intra-race, and post-race fuel. This allows your body to get comfortable with fueling while running and gives you the opportunity to identify foods that may trigger GI distress.

  • Prefuel (pre-race/workout): Especially on moderate and hard training days, add a carbohydrate-rich prefuel snack within an hour of training. Aim for a snack with 30-60 grams of carbohydrates and less than 5 grams of protein and fat to optimize digestion and absorption. Examples of carbohydrate-rich prefuel snacks include: a banana, Clif Bloks®, Stinger® waffle, or applesauce. *Find more specific recommendations on ‘Race Day’ Fueling in the section below
  • Intra-Race Fuel (during race/workout):For training sessions lasting longer than one hour, consider adding carbohydrate fuel during your run. Examples of easily-digested carbohydrate fuel include: carbohydrate beverages (e.g., Gatorade®, Maurten®, and Skratch®), banana slices, or energy gels. *Find more specific recommendations on ‘Race Day’ Fueling in the section below.
  • Refuel (post-race/workout): After each training session, refuel with a source of carbohydrates and lean protein within 90 minutes of finishing training. This timing and composition optimize muscle recovery and glycogen replenishment. Examples of refuel snacks include: a protein shake with fruit, Greek yogurt with berries, or peanut butter toast with hardboiled eggs. *Find more specific recommendations on ‘Race Day’ Fueling in the section below.

3. Hydrate Regularly

Aim for half your body weight in ounces, plus an additional 16 ounces for every hour of exercise you complete. You may need to adjust this amount based on humidity, temperature, and elevation. Electrolytes, ionized minerals in the body including sodium, chloride, potassium, magnesium, and calcium, are lost through sweat and therefore need to be replenished adequately to maintain optimal performance. Consuming electrolyte-rich foods or adding an electrolyte supplement (e.g., Nuun Sport®, Liquid IV®, LMNT®, The Right Stuff®) to your water can be helpful in maintaining hydration status and preventing muscle cramps and fatigue. Longer training runs (greater than one hour) and hot weather training present a greater need for electrolytes. *Find more specific recommendations on ‘Race Day’ Fueling in the section below.


The main goal for the week leading up to the marathon is to fuel consistently (i.e., avoid making any drastic changes to your typical fueling routine) and to prioritize carbohydrates (from fruit and complex sources), hydration, and electrolytes to prepare your body for the event. Focus on the following recommendations one week before race day.

1. Consistency

Avoid trying new foods. Focus on fueling every 3-4 hours to keep your energy up and to promote recovery.

2. Top Off Glycogen Stores

Prioritize high-quality carbohydrates (e.g., fruits, whole grains, legumes, and starchy vegetables) in meals and snacks to provide the energy your muscles need to perform.

3. Increase Hydration

Continue aiming for the goal of half your body weight in ounces with an additional 16 ounces for every hour of exercise. Consider supplementing with an electrolyte replacement drink (e.g., Nuun Sport®, Liquid IV®, LMNT®, The Right Stuff®) and consume additional electrolytes from food.

*Tip: Incorporate potassium-rich foods more frequently the week before race day to reduce your risk of muscle cramping. Potassium-rich foods include: bananas, legumes, apricots, potatoes, avocados, melon, grapefruit, prunes, beets, oranges, almonds, and spinach.


Race day is the time to implement your practiced fueling regimen. The main goal for race day is to provide your body with the energy it needs to perform at its best and, subsequently, to replenish nutrient losses and ensure proper recovery. Generally speaking, we recommend the following (will vary based on needs/goals):

1. Prefuel

  • 2-4 hours before the race: Eat a balanced meal consisting of ¼ protein, ½ complex carbohydrate, and ¼ fruit
    • For example: eggs + toast + banana
  • 30-60 minutes before the race: Eat an easily-digestible carbohydrate to provide a quick fuel source at the start of your race.
  • Hydration: Continually sip on water or an electrolyte beverage in the hours leading up to the race, aiming for a total of 16 to 24 ounces.

2. Intra-race Fuel

  • Fueling: Consume between 30-60 grams of carbohydrates per hour, depending on intensity and GI tolerance.
  • Hydration: Aim for 16-24 ounces of water or electrolyte beverage per hour.


  • Within 30-90 minutes of finishing the race: Refuel with a carbohydrate (to replenish glycogen stores and inhibit muscle protein breakdown) and a protein (to stimulate muscle protein synthesis).
    • For example: Chocolate milk + granola bar
  • Within 2-3 hours of finishing the race: Refuel with a carbohydrate-focused Balanced Plate meal (½ complex carbohydrates, ¼ lean protein, and ¼ non-starchy vegetables).
    • For example: turkey sandwich on wheat bread + baby carrots + an apple

Our team is here to ensure you are well-equipped to feel your best during training and to perform your best on race day. Do not underestimate the importance of an optimized fueling routine. If you have questions about how to fuel for your own individual goals, reach out to one of our Registered Dietitians at

Interested in a nutrition coaching program to help you prepare for an upcoming race? Check out our Fuel U Sports Nutrition Program, a 12-week performance-focused nutrition coaching program with one of our SHIFT dietitians!

In Real Health,

Rachel & Lauren

SHIFT Registered Dietitians


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