Sports Nutrition for Endurance Exercise

Runner opening energy gel packet
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Elite endurance athletes have unique sports nutrition requirements. If you exercise at a high intensity for more than two hours per day on most days, it’s essential to eat and drink appropriately for optimal performance and recovery. What, when, and how much to eat and drink can be confusing for even the most experienced athlete, but the following tips provide some general guidelines to help simplify your refueling plan.

Energy for Exercise

Before you develop your own nutrition plan, it’s helpful to review a few basic sports nutrition principles. For starters, it’s good to understand how the foods we eat (carbohydrates, proteins, and fats) help fuel muscle contractions and help keep us exercising for hours on end without fatiguing.

Carbohydrate, in the form of glycogen, is the main nutrient that fuels exercise of a moderate to high intensity. Our fat stores can also help fuel exercise, but this is mostly for low-intensity exercise over long periods of time. Finally, protein is the fuel source that is largely used to maintain and repair body tissues but isn’t normally used to generate muscle contractions.

Unlike fat, glycogen stores have a limited supply and get used up rather quickly—within about 90 minutes to two hours—during high-intensity exercise. If not replenished during this time, fatigue sets in and the athlete will need to slow down or risk hitting the wall, or "bonking." To continue high-level exercise for extended periods of time, an athlete needs to continue to refuel with easily digestible carbohydrates.

How Much to Eat

How much to eat depends upon your level of conditioning, your exercise intensity, and your body size, but the American College of Sports Medicine recommends that endurance athletes consume 30-60 grams (100-250 calories) of carbohydrates per hour in a 6%–8% carbohydrate-electrolyte solution (6–12 fluid ounces) every 10–15 min within an hour, for every hour of exercise.

What to Eat

Every athlete will have their own unique refueling needs and preferences. For example, your training partner might eat far less frequently than you do during a long training ride, but she consumes a lot more when she does eat. You might prefer to nibble constantly throughout the day to keep your energy up. So far, your personal preferences work equally well for each of you. By experimenting with different approaches, you will find your own unique refueling style that works for you.

In order to learn what foods and drinks are best for you, experiment with various foods and food combinations during your workouts. Try a variety of drinks, snacks, bars, or gels. Vary the timing of your food intake and the amount you eat as well, and over time you will be able to determine your optimal refueling style.

Some refueling options may include:

  • 16 ounces of a sports drink with added carbohydrate
  • Fruit juices
  • An energy bar with 30 grams carbohydrate
  • A banana
  • An apple
  • 2 Tablespoons of Honey
  • Half of a white-wheat bagel
  • Skim and lactose-free yogurt with fruit
  • 1 cup of skim chocolate milk

Hydration for Endurance Exercise

If you exercise intensely for more than three or four hours, you’ll need to be mindful of your hydration needs and drink water before, during, and after your exercise. Get into the habit of weighing yourself before and after long training sessions to determine your own hydration needs, and learn how different weather and training conditions may affect you. You’ll also start to get an idea of how much you need to drink during your regular workouts. Rehydrate by drinking about 24 ounces of water for every pound you lost during a workout.

Another simple way to determine your post-workout hydration status is to monitor your urine output and color. A large amount of light-colored, diluted urine most likely means you are well-hydrated. A small amount of dark-colored, highly concentrated urine may mean you are dehydrated and need to drink more water.

The following tips can help you stay on top of your fluid needs while exercising:

  • Before exercise: Drink 2-3 cups of water 20–30 minutes prior to the workout.
  • During exercise: Drink 1.5–2 cups every 5–15 minutes during the workout.
  • After exercise: Drink 3 cups of water for each pound lost at the end of the workout.

Sodium and Electrolytes

If you exercise more than 3 to 4 hours, you’ll most likely need to increase your intake of electrolytes (sodium, potassium, magnesium) beyond what you get in food alone. A marathon runner, for example, may want to train with various sodium intakes before a major event to optimize performance. An option during training and race event is to consume an electrolyte-containing sports drink, such as Nuun electrolyte replacement, during the event. This may help reduce the risk of developing hyponatremia (water intoxication).

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  1. Kerksick, C.M., Wilborn, C.D., Roberts, M.D. et al. ISSN exercise & sports nutrition review update: research & recommendationsJ Int Soc Sports Nutr 1538 (2018).

Additional Reading
  • Consensus Statement of the 1st International Exercise-Associated Hyponatremia, Consensus Development Conference, Cape Town, South Africa 2005. Clinical Journal of Sport Medicine. 15(4):208-213, July 2005.
  • Exercise and Fluid Replacement, ACSM Position Stand, American College Of Sports Medicine, Medicine and Science In Sports & Exercise, 2007.
  • Sports Nutrition Guidebook. Nancy Clark, 3rd ed. Brookline, MA: Human Kinetics; 2003.