Sports nutrition is one of the few contexts where concentrated sugar is a legitimate performance tool. The science behind when and how to use it is specific and well-researched. And significantly different from general dietary sugar advice.

Why Athletes Need Sugar During Exercise

At exercise intensities above ~65-70% VO2 max, muscle glycogen is the primary fuel. At very high intensities, muscle glycogen provides nearly all energy. A trained athlete can store 400-600g of glycogen in muscle, which provides roughly 90-120 minutes of fuel at moderate-to-high intensity before depletion.

Once glycogen is depleted, exercise intensity must drop dramatically. The phenomenon athletes call “bonking” or “hitting the wall.” At this point, the body can only run on fat oxidation and gluconeogenesis, which limits intensity to below ~55% VO2 max.

Consuming carbohydrates during exercise spares muscle glycogen and extends the time before depletion. This is the fundamental justification for in-exercise carbohydrate consumption.

The Absorption Limit: Why You Need Two Sugars

Glucose is transported from the gut into the bloodstream by the SGLT1 transporter, which is saturated at approximately 60g of glucose per hour. If you consume more than 60g of glucose/hour, the excess stays in the gut and causes gastrointestinal distress — the bane of endurance athletes.

Here’s the key discovery: fructose uses a different transporter (GLUT5). It’s not in competition with glucose absorption. By combining glucose and fructose, athletes can absorb more total carbohydrate per hour.

A 2010 study by Jeukendrup et al. found that consuming glucose:fructose at a 2:1 ratio (as in many modern sports nutrition products) allowed absorption of up to 90g of carbohydrate per hour, 50% more than glucose alone, with improved performance in endurance events longer than 2 hours.

Sports Nutrition Products and Their Sugar Profiles

Gels:

Product Serving Carbs Sugar Glucose:Fructose ratio
GU Energy Gel 32g 22g 7g glucose + maltodextrin dominant
Maurten Gel 100 40g 25g 12.5g 0.8:1 (2:1 with maltodextrin)
Clif Shot Gel 34g 25g 10g maltodextrin + fructose
Spring Energy Canaberry 83g 34g 18g real food (rice + banana)

Most gels use maltodextrin (a glucose polymer that digests rapidly) combined with fructose for the dual-transporter benefit.

Sports drinks:

Product 500ml Carbs Sugar
Gatorade Endurance 500ml 35g 35g
Maurten Drink Mix 320 500ml 80g 25g
Skratch Exercise Hydration 500ml 19g 18g
Water 500ml 0g 0g

Maurten uses a hydrogel technology (alginate + pectin) that allows higher carbohydrate concentration without GI distress by forming a gel in the stomach that slowly releases carbohydrates into the intestine.

Carbohydrate Loading

For events lasting 90+ minutes, pre-race carbohydrate loading, consuming high amounts of carbohydrate (8-12g/kg body weight per day) in the 24-72 hours before competition, increases glycogen stores. A 70kg athlete targets 560-840g of carbohydrate over 1-3 pre-race days.

Foods commonly used: white rice, pasta, bread, potatoes, bananas, sports drinks. The goal is maximizing glycogen, not minimizing sugar — this is the opposite of typical dietary guidance.

When Sugar Hurts Athletic Performance

High-sugar eating at rest. The benefits of sugar during exercise don’t apply at rest. An athlete who eats a high-sugar diet during non-training days faces the same insulin, inflammation, and metabolic consequences as sedentary individuals.

Consuming sugar 30-60 minutes before exercise. A pre-exercise sugar dose can trigger insulin secretion, which drives blood glucose down just as exercise begins, causing relative hypoglycemia during the early stages of competition. Most sports nutritionists recommend either consuming carbohydrates more than 60-90 minutes before exercise or waiting until the first 30 minutes of exercise have started.

High-sugar, low-protein diet overall. Athletes need protein for muscle repair. High-sugar processed food crowds out protein-dense whole food and leaves muscle recovery compromised.

Primary Sources

  • Jeukendrup AE. “Carbohydrate and exercise performance: the role of multiple transportable carbohydrates.” Current Opinion in Clinical Nutrition 2010
  • Burke LM et al. “Carbohydrates for training and competition.” Journal of Sports Sciences 2011
  • Thomas DT et al. “Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance.” JAND 2016