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The Role of Sugar in an Athlete's Diet

Article by Clif Bar & Company Nutrition Team with support from Bob Murray, PhD, FACSM, Clif Nutrition Advisory Council member.

The ideas and suggestions written below are provided for general educational purposes only and should not be construed as medical advice or care. Always seek the advice of a physician or other qualified health provider before beginning any physical fitness or health- and nutrition-related activity.

Carbohydrates, like sugar, often get a bad rap, but when it comes to sports nutrition, they’re king! Whether you’re riding the waves or tackling a weekend run, carbs provide crucial fuel to working muscles – helping prevent fatigue and sustain peak performance.

Why do athletes need carbohydrates?

The short answer is, energy! Carbohydrates are the body’s main source of energy.1 And for elite and everyday athletes, appropriate energy intake is the cornerstone of an optimal diet.

How much carbohydrate do athletes need?

Total energy and carbohydrate needs vary by individual. However, experts typically recommend that athlete’s get 6-10 grams of carbs per kilogram of body weight (g/kg) per day to fuel performance.2

Want to know how much you need? Check out the Active Nutrition Guide or meet with a sports dietitian to discuss a unique eating plan that’s right for you.

What type of carbohydrate do athletes need?

It’s important to remember that it’s not just about the amount of carbohydrate, the type matters too!

Simple carbohydrates
, like sugar, are ideal sources because they are quickly absorbed and made immediately available to muscles, thereby fueling the body and helping enhance performance. On the other hand, complex carbohydrates typically take longer for our bodies to break down, resulting in a slower release of energy.

While complex carbs, like whole grains and fiber, are essential ingredients in an overall healthy diet, too much before or during physical activity can cause gastrointestinal (GI) distress and impair performance.3, 4

How does sugar fuel performance?

Think of your body like a bank account and energy like cash. Much like a bank account stores money, our bodies store energy in the form of glycogen (carbohydrates stored in our muscles). During activity, athletes need to “withdraw” energy from these glycogen stores to fuel working muscles. The body has a limited storage capacity and if we “overdraw” from our energy stores, we could experience fatigue or even hit the dreaded “wall.”

Eating adequate amounts of sugar before activity (to fill up our glycogen stores) and during activity (for an infusion of immediate energy), prevents us from overdrawing our energy bank.5, 6

Athlete running up stairs

When should athletes consume sugar?

Balanced carbohydrate intake is key to keeping our bodies healthy and energized. During rest days when away from the gym, fiber-rich, complex carbs from whole foods (i.e., fruits, veggies, whole grains) should be the focus. But, when training hard or competing, simple carbs (i.e., sugars) are the body’s preferred source of fuel.2

  • BEFORE ACTIVITY: A few hours before intense, long-lasting activity, the American College of Sports Medicine recommends consuming 1-4 grams of carbohydrate per kilogram of bodyweight.2 The goal is to top up energy stores and help prevent fatigue.
    • When grabbing a pre-workout snack, look for something that’s mainly carbohydrates with only modest amounts of fiber, fat and protein. CLIF BAR® energy bars, a smoothie made with yogurt and juice, and cereal with skim milk and berries are all good choices.
  • DURING ACTIVITY: Most athletes will benefit from about 30-60 grams of carbohydrates per hour for intense activity lasting longer than 1 hour.2
    • During moderate-intensity endurance activity, foods that combine simple carbohydrates with smaller amounts of protein and fat can be tolerated and help provide sustained energy.
    • For high-intensity race-paced activity, sugar and other fast acting carbohydrates should be the sole focus. Sports drinks and performance foods like CLIF® BLOKS® Energy Chews provide an easily absorbable source of carbs to keep our muscles fueled and bodies going.

Whether you are on a long, slow ride or racing towards your personal best, remember to avoid too much fiber to help prevent bloating and GI upset.3,4

  • AFTER ACTIVITY: Protein gets all the glory when it comes to post-exercise fuel, but simple carbohydrates have a role, too.7,8,9 Within 30 minutes after activity, help replenish your energy stores and rebuild muscle with a snack that combines carbohydrates and complete protein. Some easy options include a glass of chocolate milk, the classic PB&J and protein bars like CLIF® Builders®.

What should athletes look for in a performance food?

Whole foods are an excellent foundation to anyone’s diet, but those who are active and often on-the-go can benefit from quality packaged foods, like energy bars, to help fuel performance. With that said, it’s important to be choosy when choosing the right bar.

Look out for these three ingredients to make sure you’re getting the energy you need to succeed on the bike, court, field or slopes:

  1. Total Carbohydrates: Carbohydrates are critical when it comes to sports nutrition. Look for 30+ grams of carbs per bar, the amount experts recommend getting each hour during intense, long- lasting activities.
  2. Sugar: Simple carbohydrates (like sugar) are quickly absorbed by the body, providing fast fuel to working muscles, while complex carbs (like fiber) create a slower release of energy. Fiber-rich bars low in sugar are great for an everyday snack but won’t give you the energy to power through a tough workout, plus they can cause bloating and GI upset. So, when looking for an energy bar to help optimize performance, don’t shy away from sugar.
  3. Protein & Fat: Good fats and protein are key nutrients in a healthy diet. They slow down the absorption of carbohydrates to deliver steady energy and can help curb hunger. For snacking or recovery, bars rich in protein and fats are a great choice. To fuel activity, you’ll want to look for a bar with modest amounts of protein and fat and plenty of energizing carbohydrates.


    1. Asker E. Jeukendrup (2008) Carbohydrate feeding during exercise, European Journal of Sport Science, 8:2, 77-86, DOI: 10.1080/17461390801918971.
    2. 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;116:501-528.
    3. Oostheyse T, Carstens M, Millen AM. Ingesting isomaltulose versus fructose-maltodextrin during prolonged moderate-heavy exercise increases fat oxidation but impairs gastrointestinal comfort and cycling performance. Int J Sport Nutr Exerc Metab. 2015;25:427-438.
    4. Baur DA et al. Slow-absorbing modified starch before and during prolonged cycling increases fat oxidation and gastrointestinal distress without changing performance. Nutrients. 2016;8(7): E392.
    5. Ivy JL, Lee MC, Brozinick JT, Reed MJ. Muscle glycogen storage after different amounts of carbohydrate ingestion. J Appl Physiol. 1988;65:2018-2023.
    6. Ormsbee MJ, Bach CW, Baur DA. Pre-exercise nutrition: the role of macronutrients, modified starches and supplements on metabolism and endurance performance. Nutrients. 2014;6(5):1782–1808. Published 2014 Apr 29. doi:10.3390/nu6051782.
    7. Blom PC, Hostmark AT, Vaage O, Kardel KR, Maehlum S. Effect of different post-exercise sugar diets on the rate of muscle glycogen synthesis. Med Sci Sports Exerc. 1987;19:491-6.
    8. Kerksick CM, Arent S, Schoenfeld BJ, et al. International society of sports nutrition position stand: nutrient timing. J Int Soc Sports Nutr. 2017;14:33. Published 2017 Aug 29. doi:10.1186/s12970-017-0189-4.
    9. Trommelen J, et al. Fructose coingestion does not accelerate postexercise muscle glycogen repletion. Med Sci Sports Exerc. 2016;48(5):907-12.