Is sugar really the enemy? - truefuels

Is sugar really the enemy?

The speed read: The sweet truth—why sugar matters for endurance athletes.

“Sugar” often carries a bad reputation, but it can be a vital fuel source for endurance athletes. Glucose provides a rapid energy source at high exercise intensities (Coyle, Coggan, Hopper, & Walters, 1988), fructose follows a different absorption pathway before conversion in the liver (Jeukendrup & Jentjens, 2005), and sucrose combines both for a balanced release. Used at the right times—during exercise and recovery—sugar delays fatigue, restores glycogen quickly, and supports mental focus; outside of those windows, excess added sugars can have health drawbacks.

In my experience, sugar becomes essential when it matters most in endurance sports; fueling long, high-intensity efforts, powering through the toughest training sessions, and supporting recovery and adaptation afterward.

The starting point: Sugar’s reputation—context matters

All “sugars” are carbohydrates, yet their metabolic roles differ. Excess free sugars in sedentary contexts (for example, sugary snacks in the evening) contribute to weight gain and metabolic risk. In contrast, during prolonged, high-intensity exercise, sugar becomes a valuable resource, replenishing blood glucose and muscle glycogen stores that would otherwise run low.

Technical definitions: sugars vs polysaccharides

Sugars (simple carbohydrates) comprise monosaccharides and disaccharides. Monosaccharides are single sugar units (e.g. glucose, C₆H₁₂O₆), while disaccharides consist of two monosaccharides joined by a glycosidic bond (e.g. sucrose, C₁₂H₂₂O₁₁)

Polysaccharides (such as maltodextrin), in contrast, are long-chain polymers of monosaccharide units; maltodextrins are oligosaccharides containing approximately 3–10 glucose residues produced by partial starch hydrolysis, with dextrose equivalent (DE) values that determine their rate of digestion and glycaemic impact.

What sugar really is:

  • Glucose is absorbed directly into the bloodstream and fuels working muscles almost immediately (Coyle et al., 1988).
  • Fructose, found naturally in fruits, uses the GLUT5 transporter in the intestine and is largely converted to glucose in the liver (Jeukendrup & Jentjens, 2005).
  • Sucrose is a disaccharide of glucose and fructose, offering fast and sustained energy release.

Why athletes need sugar:

  1. Immediate energy: At high exercise intensities, muscle cells preferentially oxidise glucose for rapid ATP production (Coyle et al., 1988).
  2. Delayed fatigue: Maintaining blood glucose levels prevents the sudden “bonk” associated with depleted glycogen (Ivy, Katz, Cutler, Sherman, & Coyle, 1988).
  3. Glycogen replenishment: Consuming 1.2–1.5 g·kg⁻¹ carbohydrate per hour immediately after exercise accelerates muscle glycogen resynthesis (Ivy et al., 1988).
  4. Mental clarity: Stable glucose availability supports cognitive function and decision-making during long efforts (Sünram-Lea et al., 2001).

The issue: Not all sugars are created equal

  • Simple vs. complex: Simple sugars (e.g., glucose, fructose) are absorbed rapidly, ideal during exercise but prone to rapid blood-sugar spikes if consumed at rest. Complex carbohydrates (e.g. starches) break down more slowly, offering steadier energy.
  • Natural vs. Added: Sugars in whole foods come with fibre, vitamins and minerals; added sugars in processed foods deliver “empty” calories and little nutritional benefit.

The ‘so what’: How to use sugar wisely

  • During exercise: Aim for 60–120 g·h⁻¹ of mixed carbohydrates (glucose + fructose) to maximise absorption via SGLT-1 and GLUT5 transporters and delay fatigue (Currell & Jeukendrup, 2008).
  • Post-exercise: Within 30 minutes, consume 1.2–1.5 g·kg⁻¹ carbohydrate to speed glycogen recovery (Ivy et al., 1988).
  • Daily intake: Prioritise complex carbohydrates from whole grains, fruits and vegetables. Reserve added sugars (e.g. confectionery, sweetened drinks) for occasional treats rather than daily staples.

The verdict: Sugar isn’t evil—it’s your training partner

Used strategically, sugar supports high-intensity performance, accelerates recovery and maintains mental sharpness. Consume it when your muscles and brain need it most, and limit added sugars outside training and competition to safeguard long-term health.

References

[1] Coyle, E. F., Coggan, A. R., Hopper, M. K., & Walters, T. J. (1988). Determinants of endurance in well-trained cyclists. Journal of Applied Physiology, 64(6), 2622–2630. https://doi.org/10.1152/jappl.1988.64.6.2622

[2] Currell, K., & Jeukendrup, A. E. (2008). Superior endurance performance with ingestion of multiple transportable carbohydrates. Medicine & Science in Sports & Exercise, 40(2), 275–281. https://doi.org/10.1249/MSS.0b013e31815c54ae

[3] Ivy, J. L., Katz, A. L., Cutler, C. L., Sherman, W. M., & Coyle, E. F. (1988). Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion. Journal of Applied Physiology, 64(4), 1480–1485. https://doi.org/10.1152/jappl.1988.64.4.1480

[4] Jeukendrup, A. E., & Jentjens, R. (2005). High rates of exogenous carbohydrate oxidation from a mixture of glucose and fructose ingested during prolonged cycling. Journal of Applied Physiology, 98(2), 678–686. https://doi.org/10.1152/japplphysiol.00862.2004

[5] Sünram-Lea, S. I., Foster, J. K., Durlach, P., & Perez, C. (2001). Glucose facilitation of cognitive performance in healthy young adults: Examination of the influence of fast-duration, time of day and pre-consumption plasma glucose levels. Psychopharmacology, 157(1), 46–54. https://doi.org/10.1007/s002130100771**[](https://pubmed.ncbi.nlm.nih.gov/10460314/)

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