Sugar in sports nutrition: when does it help performance and when does it harm?

Sugar is perhaps the most controversial food ingredient today. For some, it is a symbol of a "toxin", for others, a source of quick energy that the body cannot do without during exercise. The truth, as usual, lies somewhere in the middle.

Sugar as an energy source

Sugar is the primary fuel for the brain, nervous system, and muscles. During exercise, the body uses carbohydrates more efficiently than any other source — and the higher the intensity, the greater their contribution to energy production.

For endurance athletes, carbohydrates account for 60–70% of total energy intake , some of which may also come from simple sugars (glucose, fructose, sucrose). They are therefore not necessarily harmful — the context is crucial: when, how much and in what form they are consumed.

When does sugar become a problem?

A health problem occurs when the intake of added sugars is higher than the body can use over a long period of time. The excess energy is stored as fat and contributes to obesity, insulin resistance and cardiovascular disease.

According to WHO recommendations, added sugars should make up no more than 10% of total daily energy intake , ideally less than 5% (which corresponds to about 25 g per day for an average adult). For comparison – a regular energy gel contains about 20–25 g of carbohydrates, i.e. almost the entire daily amount. But the difference is crucial: an athlete burns the gel within a few minutes.

Glucose vs. fructose — not sugar is like sugar

Glucose is absorbed quickly and directly increases blood sugar levels. Fructose is metabolized more slowly and partially in the liver, which can be advantageous during prolonged exercise — it allows for the simultaneous use of two transport pathways (GLUT1 and GLUT5).

Therefore, it makes sense to combine glucose and fructose in a 2:1 ratio, as modern sports drinks do. This can increase carbohydrate absorption up to 90 g per hour without digestive problems.

Added sugars vs. natural sugars

From a metabolic perspective, glucose from an orange is no different from glucose from a soda — the difference is what accompanies it. Fruit and whole grains also contain fiber, vitamins, minerals, and antioxidants. These reduce the glycemic effect and contribute to better regeneration.

Conversely, foods high in added sugars (sweetened beverages, cereals, baked goods) have low nutritional density — they provide energy but almost no nutrients.

Sugar and the brain

Glucose is the only direct source of energy for the brain.
During long training or racing, its decline can lead to fatigue, slowed reactions, and loss of concentration. Studies show that carbohydrate supplementation, including through mouth rinses, can improve performance during high-intensity exercise lasting 45–60 minutes.

In other words: even if sugar does not enter the bloodstream, the mere contact with the oral mucosa activates brain areas associated with motivation and performance.

Why Athletes Need Sugar (and When They Don't)

During exercise, sugar is not a problem , but a solution:

• replenishes glycogen stores,

• delays fatigue,

• supports performance and regeneration.

After exercise, it makes sense to supplement with 1.0–1.2 g of carbohydrates per kg of body weight within the first hour, ideally in combination with protein (in a 3:1 ratio). However, on non-training days, the less added sugar, the better.

Summary

How not to get lost in it

1. Distinguish the purpose: sugar during exercise = fuel; sugar while watching TV = excess.

2. Use combined sources: glucose + fructose will improve absorption and reduce digestive problems.

3. Check the ingredients: make sure added sugar is not the first item in the ingredients list.

4. Don't rely on "sugar-free" labels: products with artificial sweeteners may have other pitfalls.

In conclusion

Sugar is not the enemy — it's a tool . It just depends on when, how much, and why you use it. At the right moment, it can boost performance and recovery. At the wrong moment, it becomes an unnecessary burden.