Prins et al. — American Journal of Physiology, 2025
The Science Behind BSE.
All brands offer between 90-120g of carbohydrates per hour. We were the only ones to ask why. Here's what the research actually says.
Each effort uses a different fuel
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The body primarily burns lipids. This is the training zone for metabolic flexibility.
Dominant Fuel: Lipids 70-90%
Carbohydrates Needed: 0-20g/hour
BSE Product: FUEL ZONE 2
Mixed zone — lipids and carbohydrates contribute in varying proportions depending on the level of metabolic adaptation.
Dominant fuel: Mixed
Carbohydrates needed: 15-60g/hour
BSE product: FUEL TEMPO
High intensity. Carbohydrates become the primary fuel. Ratio and quantity are critical to avoid digestive issues.
Dominant fuel: Carbohydrates
Carbohydrates needed: up to 90g/hour
BSE Product: FUEL ULTRA + FLUID ULTRA SHOT
Metabolic Flexibility — What the Science Confirms.
The body's ability to utilize carbohydrates during exercise is not unlimited.
Glucose can be absorbed and used at a high rate, while fructose follows a different metabolic pathway. This is why the glucose/fructose combination is now widely used in sports nutrition: it allows for increased energy intake while improving digestive tolerance during prolonged efforts.
However, optimal intake always depends on the context.
During fundamental endurance sessions (Zone 2), athletes with good metabolic flexibility are able to use lipids more as an energy source and reduce their reliance on carbohydrates.
As intensity increases, the contribution of carbohydrates becomes more important. Energy needs evolve with effort, and the nutritional strategy must evolve with them.
At BSE, we do not seek to eliminate carbohydrates. We seek to use the right fuel at the right time.
Source: Prins, Noakes et al. — Carbohydrate ingestion eliminates hypoglycemia and improves endurance exercise performance in triathletes adapted to very low- and high-carbohydrate isocaloric diets. American Journal of Physiology — Cell Physiology, 2025.
Why does the industry recommend 80-120g/hour?
Current recommendations are based on the maximum oxidation of exogenous carbohydrates — not on actual performance. Recent studies, including Prins 2025, show that 10g/hour is enough to prevent hypoglycemia and improve performance by 22%. Increasing doses beyond 60g/hour of pure glucose leads to digestive issues with no proven benefit on performance.
Is fructose really used by muscles?
Fructose passes through the liver before entering the bloodstream—unlike glucose, which is directly available to muscles. Current data shows that fructose is not directly used by muscles during exercise. The 2:1 glucose/fructose ratio allows the use of two different intestinal transporters to absorb more carbohydrates without saturating the intestine—but the direct muscular contribution of fructose remains limited according to available data.
Why 90g/hour maximum at BSE?
FUEL ULTRA provides 30g of carbohydrates (2:1 glucose/fructose ratio). FLUID ULTRA SHOT provides up to 60g/hour (3:1 dextrose/fructose ratio). Combined: maximum 90g/hour. Beyond this, data does not support additional performance benefits, and the risk of digestive issues significantly increases. Until new data is available, BSE remains at this ceiling.
How long does it take to develop metabolic flexibility?
Minimum 4 weeks according to Prins et al. 2025. During the first few weeks, Zone 2 performance may slightly decrease — this is normal, it's adaptation. From week 4-5, lipid oxidation significantly improves and the carbohydrate crossover point increases from ~60% to 75-80% HRmax for well-adapted athletes.
First drop — Presale open
Ready to train your metabolism?
FUEL ZONE 2 — Macadamia Salt Puree. Less than 4g of carbohydrates. Designed for Zone 2 and metabolic flexibility.
