How Much Carbohydrate Per Hour?

The one change that turns a bad last hour into a good one — and the physiology behind the numbers.

What this is

Carbohydrate intake during long exercise used to be capped at around 60 g per hour, because that's the ceiling on how fast glucose alone can be absorbed through its intestinal transporter.

Then researchers combined glucose with fructose, which uses a different transporter. Because the two absorb in parallel rather than competing, total oxidation rates rise substantially, and guidance for events lasting beyond about two and a half hours moved to roughly 90 g per hour of multiple transportable carbohydrates. That's the physiology behind every 2:1 glucose-to-fructose gel on the shelf.

What the evidence says

  • Single-source carbohydrate oxidation plateaus around 60 g per hour

    Gold· human data

    The classic finding, set by intestinal transporter capacity for glucose.

  • Glucose plus fructose raises usable carbohydrate intake substantially

    Gold· human data

    Using separate transport pathways lifts oxidation rates well above the single-source ceiling, which is why 90 g per hour became the recommendation for long events.

  • The gut can be trained to tolerate higher intakes

    Silver· human data

    Practising race-day fuelling in training improves tolerance and reduces gastrointestinal symptoms. Reasonably supported and universally recommended by practitioners.

  • More is always better

    Not supported

    Intake is limited by gut tolerance, and exceeding it produces exactly the distress you were trying to avoid. Requirements also scale with duration and intensity — a 45-minute session needs none of this.

What this means in practice

  • Match intake to duration: short sessions need nothing, and the higher intakes apply to events beyond roughly two and a half hours.
  • Choose products using multiple carbohydrate sources if you're targeting the higher end.
  • Practise your fuelling plan in training at race intensity — the gut adapts, and race day is the wrong place to discover it hasn't.
  • Take fluid and sodium into account alongside carbohydrate, particularly in heat.
  • Work backwards from the event: total duration, target per hour, then how many gels, bottles or bars that actually is.

The honest summary

For long events, around 90 g per hour of mixed glucose and fructose is the well-supported target, and gut training is what makes it achievable. For anything under an hour, none of this applies.

Work it out

See also

Related

Frequently asked questions

How many carbs per hour for a marathon?
Guidance for events beyond about two and a half hours is roughly 90 g per hour of multiple transportable carbohydrates, subject to gut tolerance — which is trainable. Shorter events need less.
Why do gels use glucose and fructose?
They use separate intestinal transporters, so they absorb in parallel instead of competing. That's what lifts total carbohydrate oxidation above the single-source ceiling.

Sources

Written and reviewed by Mathew Beale, MSc Biotechnology, University of Reading.

Last reviewed: