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Water, Carbs and Race Day Eating: What Endurance Athletes Should Know

closeup of handing off water bottles during a race

Endurance athletes experience significant sweat and energy losses that need to be replaced for proper performance. Here is advice from UH Sports Medicine on how to prepare for an endurance event.

Early Preparation

Prep for your race about a month before. You will need to collect some basic information.

  • What nutrition will be provided at the race?
  • Where are the water and nutrition stops on the course?
  • Keep an eye on the weather conditions.
  • Pack your groceries for the night before the race or make a reservation at a place where you are confident the food will be good.

Finding out what nutrition will be provided at the race will give you the ability to plan before race day. If you cannot tolerate what is provided, you'll have ample opportunity to find other options.

Practice Your Plan

  • Find the nutrition products that work best for you. Two necessary items: energy (carbs) and hydration. Your gut is extremely trainable and tolerance of products is attainable.
  • Timing – once you find where the nutrition stations are mapped, practice fueling at those certain stops to see what timing works best for you.
  • Build up to it and don’t do a complete overhaul. Start adding in sports drinks – this will help combine energy and hydration.  Once you master this, add in nutrition products.
  • Practice with nutrition that will be offered at the race, if you cannot tolerate them, practice with items that work for you.

Carb Loading: Do or Don’t?

Now a thing of the past, days of extreme carb loading regimes have dwindled. The thought was to ensure muscles were loaded with glycogen (enough energy).  Research now shows very high muscle glycogen can be achieved by eating more carbohydrates throughout the day and at meals.

The increase in carbs and portions should mimic your training. As miles go up, portions should too, but this doesn’t mean eating as much as possible. 

The day before the race, have your largest meal at lunch and a lighter meal at dinner. Be sure to practice this, too. Additionally, if gastrointestinal issues are a concern, reduce fiber intake the day before and morning of the race.

On Race Day

Pre-Race Breakfast

  • Rely on personal preferences and don’t deviate from what you’re used to.
  • Consume at least 100 grams of carbohydrates
  • Eat three to four hours before the race
  • Drink water! Check your urine, if it’s dark, keep drinking, if it’s lightly colored, you know you have done a good job hydrating. Don’t start the race at a deficit.

An Hour Before

  • Bring your water bottle to sip on fluids
  • Take a gel or gummy about 15 minutes before – this will help “top off” your fuel stores
  • Too much fluid or fuel can cause an upset stomach

During The Race

  • Follow what you practiced.
  • With carbs, 30 grams to 60 grams per hour is a good rule of thumb. An athlete finishing under three hours may need a little more, and someone in the four- to five-hour range would be OK with 30 grams an hour.
  • Carbohydrate sources can include: one banana (24 to 30 grams); gel (21 to 27 grams); energy bar (20 to 40 grams); four to five chews (16 to 25 grams); 10 jelly beans (11 grams)

Caffeine has been used by some runners with good outcomes. But this also needs to be practiced before race day.


  • Drink water to replenish but don’t overdo it.
  • Be sure to choose a good post-race meal to ensure good muscle recovery – carbs, lean protein and veggies.
  • Celebrate your achievement and indulge -- but in moderation.
  • Be sure to externally recover, too! Use ice and foam rollers on your muscles to avoid injury and soreness. Stretch and sleep.

Other Tips To Keep In Mind

Always try new things out in training -- never in competition! You never know what can happen on race day.

In the weeks and days leading up to competition, continue to eat an adequate protein (0.6 to 0.7 grams per pound or 1.3 to 1.5 grams protein per kilogram of body weight) to help glycogen synthesis and as an alternate fuel source in endurance exercise.

Add some fiber-rich foods to promote regular bowel movements but not so much as to cause constipation. There is a fine line between diarrhea and constipation, and you don’t want to learn about it on Race Day.

Expect some weight gain of about 2 to 4 pounds. For every ounce of glycogen, the body also stores 3 ounces of water. Although your muscles may feel a little heavier at the beginning of the race, these feelings will subside as the body uses up the glycogen and water throughout the event.

Use various forms of carbohydrate-dense foods and drinks to meet your needs, such as juices, gels and sports drinks. Be sure to consume whole-grain sources as well to balance out all that sugar.

Most important of all, do not wait until your last meal to load up on the carbohydrates. You want to give your body time to digest. A big meal at night may leave you feeling full and uncomfortable in the morning.

Eat your largest meal early in the day before competition.

Finally, be sure to still consume some energy sources and fluids during your event. Make sure to stop at the water stops, use your water, sports drinks and gels as needed. What you have stored up will help you go longer, but it still may not be enough to get you through the entire race without an additional fueling plan.

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University Hospitals Sports Medicine takes a multidisciplinary approach that integrates care from medical experts who specialize in the diagnosis and treatment for athletes of all ages and abilities. Our fellowship-trained sports medicine specialists, primary care doctors, nutritionists, sleep experts and other healthcare professionals ensure the very best in health and medical care for athletes. Learn more about UH Sports Medicine.