Too few carbs: bonk. Too many: stomach cramps. Somewhere in between is your perfect fueling – and getting there is simpler than you think.

This guide breaks down how many carbohydrates you actually need while cycling and running, how to plan for your specific session, and what that means in practice.

Why Carbohydrates Matter So Much in Endurance Sport

Your body has two main energy stores: fat and carbohydrates (glycogen). Fat is almost inexhaustible but slow to access. Carbohydrates are limited – around 400–600 g of glycogen in muscles and liver – but fast and available, especially at higher intensities.

At low pace, you burn a lot of fat. As intensity rises, your body shifts increasingly to carbohydrates. The problem: after 60–90 minutes of hard effort, glycogen stores are depleted – and without refueling, you slow down, lose power, or completely fall apart.

The bonk isn't a myth. It's biochemistry.

The Recommendation: How Many Carbs Do I Need?

Current sports nutrition science recommends 1.0–1.5 g of carbohydrates per kg of body weight per hour for endurance sport, depending on intensity and training status (Jeukendrup, 2014; Thomas et al., 2016). For a 70 kg athlete, that's 70–105 g/h at high intensity.

Cycling

Running

Running follows similar rules – with one key difference: the stomach gets shaken up more while running. That limits absorption capacity.

Rule of thumb for both sports: Start planning fueling from 60 minutes. Take it seriously from 90 minutes onwards.

Why "As Much As Possible" Isn't a Good Strategy

More isn't always better. The gut can only process a limited amount of carbohydrates per hour – for most people around 60 g, when using a single carbohydrate source (glucose).

By combining glucose and fructose, absorption capacity rises to around 90 g/hour. Well-trained athletes can push this to 100–120 g with specific gut training (Jeukendrup, 2014).

Taking in more than the gut can handle risks: nausea, cramps, diarrhea. Not a great picture at kilometre 35.

Glucose and Fructose: Why the Mix Matters

The gut has two different transporters for carbohydrates:

• SGLT1 transports glucose
• GLUT5 transports fructose

Using both simultaneously essentially doubles absorption capacity. That's why modern sports nutrition products often combine maltodextrin (glucose-based) and fructose.

The Chumy Gel-Mix already accounts for this – so you don't have to figure out the ratio yourself.

Timing: When Do I Eat What?

The "Start Early" Principle

The most common mistake: eating only when you already feel tired. By then it's often too late – blood sugar has dropped, energy is gone, and it takes another 15–20 minutes for the gel to actually work.

Better: Start fueling before you feel like you need it. On long sessions: from minute 30–45.

Practical guidelines

• Every 20–30 minutes a small carb portion (approx. 20–30 g)
• Spread it out rather than one big dose at once
• Always chase with water

Gel-Mix vs. Drink-Mix: What to Use When

In practice, many athletes combine both: Gel-Mix for quick carbs, Drink-Mix in the bidon for steady supply and electrolytes.

How to Calculate It for Your Session

Simple formula:

Session length in hours × carbs/hour = total need in grams

Examples:

• 2h gravel ride, medium intensity: 2 × 60 g = 120 g carbs
• 4h road ride, high intensity: 4 × 90 g = 360 g carbs
• Half marathon, 1:45h: 1.75 × 50 g = approx. 88 g carbs
• Marathon, 4:00h: 4 × 70 g = 280 g carbs

With a self-mix gel, you can prepare exactly this amount – instead of relying on fixed portion sizes that may not match your needs.

Frequently Asked Questions About Carbs in Sport

Do I really need to think about carbs as a hobby athlete? From one hour of effort: yes. Not because you need to optimise performance, but because you'll lose more energy than necessary – and the second half of your session will be a lot less fun.

What's better: gel or bar? Depends on intensity. At high pace, the stomach often struggles with solid food. Gels and drink mixes are easier to digest. Bars work well at lower intensity and on long sessions where solid food is welcome.

Can I fuel with real food? Yes, especially at lower intensity and on ultras. Bananas, dates, rice balls – all fine. But at high intensities and in races, liquid/gel-format carbohydrates have a clear edge: faster absorption, easier digestion.

Should I take the same amount in training as in a race? Not necessarily. But training your fueling is valuable – the gut can learn to handle larger amounts. Start lower and build up.

How do I avoid stomach problems? Never try new products in a race. Always chase concentrated gels with water. Spread small portions over time rather than taking one big dose.

The Bottom Line: Smart Carbs, Not Rigid Rules

There's no universal answer to "how many carbs" because every body, intensity, and session is different. But with the guidelines in this article and a gel mix that adapts to your needs, you're well set up.

Your fueling, your rules.

Discover the Gel-Mix → Carb & Electrolyte Drink-Mix →

Sources: Jeukendrup, A.E. (2014). A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise. Sports Medicine, 44(S1), 25–33. Thomas, D.T., Erdman, K.A., Burke, L.M. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501–528.

Less waste, more taste. – Chumy