jill
January 10, 2026
jill
January 10, 2026
High-carbohydrate fuelling is everywhere in cycling right now, but does ‘more’ always mean ‘better’?
As a nutritionist, who specialises in ultra-endurance, I want to step back from the hype and bring the conversation back to physiology, context, and the realities of long-duration performance.
Performance runs on energy in the form of ATP – not grams of carbohydrate
Miles and muscles don’t run on food directly. They run on Adenosine Tri-Phosphate (energy) produced inside the mitochondria via metabolic processes that draw on carbohydrate, fat, and (in limited cases) amino acids. Training increases mitochondrial density and capacity, which in turn increases the ability to produce ATP.
Carbohydrate is a key substrate in that system. But the relationship isn’t as simple as:
more carbohydrate → more ATP → more performance.
Why 100–120 g/hr shouldn’t be a universal target
Of recent, you hear figures of 100–120 g/hr, sometimes even higher, quoted from elite cycling environments. But an athlete’s ability to ingest, absorb, and oxidise carbohydrate depends on multiple factors, including:
- total and lean body mass
- absolute work rate (wattage over time)
- aerobic capacity
- environmental conditions
- gut tolerance, hydration status, and fatigue
- carbohydrate type & concentration
- presence of co-nutrients (e.g., electrolytes, caffeine)
For athletes capable of very high aerobic output, the evidence thus far suggests that higher hourly intakes don’t necessarily improve performance but they do seem to protect day-to-day energy availability and recovery, particularly in stage racing.
But that doesn’t automatically translate to the club rider, time-crunched amateur, or ultra-endurance athlete riding for 12 – 100 hours, and beyond.
Intake doesn’t translate to oxidation
Emerging work including isotope-labelled substrate studies in pro settings suggests that not all ingested carbohydrate is oxidised. In some trials, only 70% of a 120 g/hr intake was oxidised, with wide variability between individuals.
The remainder doesn’t disappear. It accumulates in the gut, which matters a great deal more in ultra-endurance time scales than in a 3–5-hour race.
Bottom line, it’s not what you can ingest that matters, it’s what you can absorb and oxidise.
The potential downsides of chronically pushing very high carb
A recent review of high carb fuelling strategies published in in Sports Medicine (Nov 2025) highlights several possible consequences of sustained high carbohydrate fuelling, particularly when it outpaces oxidation capacity:
- suppressed fat oxidation (dose-dependent)
- accelerated glycogen turnover
- gastrointestinal disturbance
- potential blunting of mitochondrial adaptation
None of these automatically mean ‘don’t use carbohydrate’ at higher doses (doses above 60-90 grams/hour) They simply mean context matters.
Why this matters even more for ultra-racers
Ultra-racing, more than any other form of racing, depends on metabolic flexibility – the ability to efficiently oxidise both fat and carbohydrate over very long durations, most of which occur below anaerobic threshold.
Gram for gram, fat provides almost twice the energy yield of carbohydrate, and in ultra-events it is a critical metabolic partner.
My bias, based on years in this space, is simple:
I would rather train your metabolism to oxidise more fat than train your gut to tolerate ever-increasing carbohydrate loads that may or may not be oxidised.
Gas, bloating, nausea, and reduced output during the back half of an event are often not “bad luck”. They can be the downstream effect of unoxidised carbohydrate accumulating hour after hour.
Of course, the sweet spot is the goal – the right amount of carbohydrate over the right amount of time, that supports continued output while aligning hydration, environment, terrain, and gut capability.
This means looking at carb grams per hour, with the introduction of larger amounts of carb placed strategically (carb cycling).
So, how much carbohydrate makes sense?
There is no single number that applies to all riders. Intake should reflect:
- lean body mass
- aerobic capacity
- event duration and intensity
- gut tolerance and history
- body composition goals
- environmental demands
- real-world performance feedback
In practice, post consult where all of the above are discussed, I typically start my clients on a baseline of 0.5–0.7g carbohydrate per kg lean body mass per hour, then adjust according to the athlete’s lived experience in various training sessions, as well as data curves.
I work closely with my athletes, so adjustments happen quickly, especially as training ramps up and aerobic capacity, work rate, and muscle mass changes. Tools like FatMax testing are useful for tracking metabolic progression but a 20-minute protocol simply cannot predict what happens over 12, 24, or 72 hours on the road.
The bottom line
Carbohydrate fuelling is nuanced, dynamic, and deeply individual.
The goal is not to chase the biggest number – it’s to match intake with physiology, context, and performance demands, while preserving the adaptations that ultra-endurance athletes depend on.
Stay observant. Notice when you feel strong, when output drops, and when the gut starts talking back. That mix of objectives and subjective data is everything.
In the end…you’re the only sample size that counts.
Every rider’s metabolism and gut tolerance are unique. If you’d like guidance to find your ideal fuelling strategy, get in touch and we’ll work it through together.
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