Sugar for “Energy” During Training: An Evidence-Based Perspective
As a registered dietitian, certified personal trainer, and ski race coach, I often see athletes come to training with candy, gummies, and other sugary snacks intentionally chosen to “keep energy high.” While carbohydrates are essential for performance, the belief that frequent sugar intake is necessary for training deserves closer attention.
How the Body Fuels Intermittent Training
Many sports involve intermittent effort, short bursts of activity lasting approximately one to two minutes followed by several minutes of recovery. Examples include skiing, tennis, football, and some track events. Even when total training lasts several hours, the continuous high-intensity workload is limited. Recovery intervals allow phosphocreatine stores to regenerate and oxidative metabolism to resynthesize ATP between efforts, supporting repeated bursts of activity. ATP is the primary energy currency the body uses to perform work.
To generate needed ATP, the body is metabolically flexible, deriving energy from carbohydrates, fats, and to a small extent protein. As exercise intensity rises, carbohydrates do become the dominant fuel because they can be metabolized rapidly to support higher power output.
However, even without simple sugar intake during training, the body maintains adequate glucose, the primary circulating fuel carbohydrate, through several mechanisms. Muscles store glucose as glycogen, which is used by working muscles. The liver can also break down its own glycogen stores, releasing more glucose into the blood. The liver can also produce glucose from other substances in the body, including glycerol released from stored body fat.
Although amino acids may contribute when carbohydrate availability is low, protein typically provides only a small portion of exercise energy under normal conditions. When athletes begin training adequately nourished, muscle performance during intermittent exercise is not compromised by avoiding simple sugars mid-session.
Fat oxidation increases during lower-intensity periods and recovery intervals, and during longer sessions the body can utilize fatty acids and ketone bodies to help spare glucose. Consequently, pre-existing muscle glycogen stores and circulating fatty acids are generally sufficient to sustain performance during intermittent training.
In contrast, the situation differs during continuous endurance exercise lasting longer than approximately 90 minutes at high intensity, during which glucose oxidation is high, liver glycogen can become depleted, and carbohydrate in the form of added sugars can delay fatigue, improving performance.
Potential Downsides of Routine Added Sugar Use
Frequent reliance on candy during training increases added sugar intake. The American Heart Association recommends children limit added sugars to less than 25 grams per day, yet a small serving of gummies can approach this amount.
Rapid ingestion of simple sugars may also cause gastrointestinal discomfort or perceived energy fluctuations. Some athletes report shakiness, nausea, or a perceived “energy crash” when large amounts of sugar are consumed shortly before or during activity.
Regularly pairing exercise with ultra-sweet snacks may also condition young athletes to associate candy with athletic performance, reinforcing preferences for highly sweet foods and the perception that sugary snacks are necessary for training.
Conclusion
Carbohydrates are essential for sustained high-intensity and prolonged endurance exercise. However, during most intermittent training sessions, even those lasting several hours with short bursts of effort and recovery, additional simple sugar intake is usually unnecessary if athletes begin well fueled and hydrated. When extra fuel is needed, portable whole-food carbohydrate sources such as fruit, dates, or pre-cooked sweet potatoes provide energy without added sugars. For long-term performance and recovery, refueling after training with balanced, nutrient-dense whole foods remains most important.
Patrick Traynor, PhD, MPH, RD, CSOWM, CPT, is a registered dietitian and founder of MNT Scientific, LLC (MNTScientific.com), an insurance-based nutrition practice serving South Lake Tahoe, CA; Minden, NV; and Ashland, OR. He holds the Interdisciplinary Specialist Certification in Obesity and Weight Management (CSOWM) from the Commission on Dietetic Registration. Virtual appointments are available via telehealth. For inquiries or appointments, visit MNTScientific.com, dial (530)429-7363, or email info@mntscientific.com.
