Never again will you experience a bonk or energy crash! What you need to know about your blood sugar in cycling.

When a ride on the road bike gets long, intense, or both, one thing matters above all: energy. Blood sugar levels play a crucial role in this. But what exactly is the glycemic index (GI) ? And how can you use this knowledge for better fueling during training ?

By Vincent Augustin 2 minutes read time

About the author Vincent Augustin

Vincent founded MYVELO together with Fabian. The two share a long-standing passion for cycling. Together they have cycled thousands of kilometers and fought for victories in the German racing bike league. The idea of founding MYVELO arose from their many years of experience and knowledge of what makes a good bike. Find out more about MYVELO now

Published: December 20, 2025

What is the glycemic index?

The glycemic index (GI) indicates how quickly a carbohydrate-containing food raises blood sugar levels . Glucose, with a GI of 100, serves as the reference. The higher the GI, the faster blood sugar levels rise – and the faster energy is available.

High GI (>70) : e.g., white bread, glucose, rice cakes
Medium GI (56–69) : e.g., bananas, oatmeal
Low GI (<55) : e.g., lentils, apples, whole-grain bread

Why is the GI important for road cyclists?

During intense rides or races, the body primarily relies on carbohydrates as an energy source. Depending on their glycemic index (GI), these can be metabolized more or less quickly.

Before training : A low to medium GI prevents blood sugar spikes and resulting energy crashes. Ideally, take 1–2 hours before starting.
During training : Quick energy is crucial. A high GI ensures rapid glucose availability – important for long rides or intervals.
After training : A high GI can help to quickly replenish glycogen stores – especially during short recovery periods between training sessions.

Blood sugar and performance

Blood sugar levels fluctuate throughout the day and during physical exertion. When cycling, performance is closely linked to the availability of glucose – especially during prolonged or intense exertion.

Stable blood sugar protects against performance drops (“bonk” or “hunger hit”).
A rapid drop in blood sugar levels can trigger dizziness, concentration problems or nausea – the classic “flat foot in the body”.

Fueling during training – practical tips

Short trips (<90 minutes):

No additional fueling is needed if glycogen stores are well filled.
Water or an electrolyte drink is often sufficient.

Longer journeys (>90 minutes):

From the 60th minute onwards, you should regularly consume energy – about 30–60 g of carbohydrates per hour .
Good sources:
- Energy gels (high GI, quickly available)
- Rice bars or dried fruit (medium GI)
- Banana (natural mix of glucose and fructose, medium GI)
- Sports drinks with glucose & maltodextrin

Tip: For longer tours, pay attention to a combination of glucose + fructose in a ratio of 2:1 – this increases the maximum absorption capacity to up to 90 g of carbohydrates per hour.

Competition simulation:

Those who race should test their fueling during training . Digestion, GI tolerance, and personal preferences vary.

Example of a 3-hour training ride

Breakfast (2 hours beforehand) : Oatmeal with banana and nuts (medium GI)
During the journey :
- One energy gel every 30 minutes (20–25 g carbohydrates, high GI)
- Additionally, half a bar or a banana every 60 minutes.
- 500–750 ml of fluid per hour, possibly with electrolytes
After the ride : white bread with jam or a recovery drink (high GI)

Conclusion

The glycemic index isn't dogma, but it's a helpful tool – especially for athletes. Those who manage their blood sugar intelligently can perform better, last longer, and recover faster. The motto is: low GI before training, high GI during and after .

For all ambitious cyclists, fueling is an integral part of training, not an add-on.

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