Home » Nutrition for Athletes Part 3: During Exercise

Nutrition for Athletes Part 3: During Exercise

Submitted by Amy Sercel MS RD CD

Edited by Marcia Bristow MS RDN CSSD CD

Eating balanced meals on a day-to-day basis and fueling properly before exercise has a huge impact on the way you feel and perform.  It’s just as important, however, make sure you continue to fuel and hydrate during exercise.  During exercise, the goals of refueling include replenishing your carbohydrate stores, fluids, and electrolytes.


As you exercise, your muscles get energy from the glycogen your body has stored in your muscles and liver.  During exercise that lasts for less than 45 minutes, you won’t experience any negative effects of this.  In longer activities these stores get used up you might feel tired and less able to concentrate.  Eating carbohydrates can help prevent you from using up these stores and keep you performing at your peak.  Re-fueling regularly is especially important if you’ll be exercising for two hours or more, when higher carbohydrate intake has been linked to improved athletic performance.1 As with eating just before activity, it’s best to choose sources of carbohydrates that are digested easily, so they don’t weigh in your stomach and slow you down.  You’ll also want to avoid foods that are high in fiber and fat.

It’s recommended that you get about 0.5 grams of carbohydrates per pound of your body weight per hour of exercise, either through a sports drink or through more easily digested carbohydrate foods.2 For example, a 150-pound person would need about 75 grams of carbohydrates per hour.  You could get this by eating four medjool dates or a large banana with a 20-ounce sports drink.  The amount of time you’ll have to eat during exercise will vary based on your sport.  If you don’t have time to eat a full meal, sports drinks or supplements like GU can give you the carbohydrates you need to stay fueled.  Practice re-fueling with carbohydrates during exercise so you’ll know which foods work best for you and won’t run into any surprises on the day of your competition.


If you get dehydrated during exercise, you’ll probably feel lower endurance levels and have trouble concentrating.  More severe dehydration can even lead to decreased blood flow to your muscles and significantly lowered exercise endurance.1 To prevent this, aim to drink between ½ and 1 cup of a sports drink that contains carbohydrates and electrolytes per hour of activity.  Look for sports drinks that list glucose, maltose, dextrose, or maltodextrin as the first ingredient, as you’ll be able to digest and absorb these sugars more easily than fructose or sucrose.

You can get an idea of the amount of fluids you need to perform your best by experimenting with hydration in your training sessions to learn your sweat rate.  Weigh yourself before and after activity; a loss of 1 pound represents a loss of about two cups of fluid, and you’ll need to drink that much fluid to ensure that you stay properly hydrated.1 Losing more than 2% of your starting body weight is considered excessive fluid loss, and will lead to fatigue and impaired exercise performance.  For a 150-pound person, this would mean losing 3 pounds during activity.


When you exercise for more than two hours in a row, you will also need to replenish the electrolytes lost in your sweat: sodium and potassium.  Taking in too much water without replenishing these electrolytes can lead to “water intoxication,” or overhydration.  This can lead to nausea, vomiting, confusion, seizures, and even loss of consciousness and death.1 Sports drinks are fortified with electrolytes, and foods like fresh or dried fruits, pretzels, or crackers will also provide sodium and potassium as you exercise.

Keeping your carbohydrate stores high, replenishing your electrolytes, and staying hydrated during exercise will help you make sure you perform your best.  For individualized recommendations, talk to a Registered Dietitian who can make you a plan that will work for your food preferences and athletic goals.


  1.  Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Acad Nutr Diet. 2016;116(3):501-528.
  2.  Sports, Cardiovascular, and Wellness Nutrition. Fueling for Performance: How proper timing of meals affects both sport and academic performance. NCAA.org – The Official Site of the NCAA. http://www.ncaa.org/health-and-safety/nutrition-and-performance/fueling-performance-how-proper-timing-meals-affects-both. Published December 18, 2013. Accessed March 29, 2017.

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