How Many Carbs You Can Absorb on Course: The 60 and 90 Gram Rule

A familiar scene: an athlete on a long start swallows gel after gel, and by the third hour the "wall" hits anyway — plus a heavy stomach. The problem isn't greedy muscles. The bottleneck is the gut. Asker Jeukendrup's classic work explains how many carbohydrates the body is physically able to take in during exercise and how to push that ceiling higher. Let's unpack the numbers and turn them into working schemes.

Why the ceiling is around 60 g/h

Carbs from a drink or gel don't enter the blood directly: first a transporter protein has to "pump" them across the gut wall. For glucose that transporter is SGLT1, and it has a throughput limit.

The key takeaway from the research: if you eat glucose alone (or maltodextrin, which breaks down into glucose in the gut), the body oxidizes it at a rate no higher than 1 g/min — that is, roughly 60 g/h. Eat more and the excess won't be absorbed; it lingers in the GI tract, pulling water toward itself. Hence the sloshing, nausea, and diarrhea. That's exactly why pouring in 80 g of pure glucose per hour is pointless and even harmful: the ceiling is the same.

How to raise the bar to 90 g/h

The trick is that fructose has a different transporter — GLUT5. It works independently of SGLT1, meaning it opens a second "pipe" into the blood.

If you mix glucose and fructose, total carbohydrate oxidation rises noticeably above 1 g/min — experiments recorded up to 1.26 g/min, roughly 75% more than from a single source. A practical target for ultra-long efforts is around 90 g/h. The optimal ratio in the blend is 2:1 glucose:fructose.

Important: this only works with "multiple transportable carbohydrates." The form barely matters — a drink, gel, or bar is absorbed similarly. And another piece of good news from the data: the absorption rate does not depend on body mass and is weakly linked to fitness level, while it's about the same for runners and cyclists. In other words, 90 g/h is not a privilege of the elite.

How many grams for your distance

More isn't always better. Fuel needs grow with the duration of the effort, not with ambition. Benchmarks from the literature:

Up to ~45–60 minutes: carbs are barely needed as fuel. A mouth rinse with a carbohydrate solution is enough — the brain "reads" the sugar in the mouth and gives a boost, even if you spit the drink out.
1–2 hours: small amounts of carbs already have an effect; no need to rush to the maximum.
2–3 hours: the working range is up to ~60 g/h, and a single source (glucose/maltodextrin) can handle it here.
Ultra-long, more than ~2.5–3 hours: the target is higher — around 90 g/h, and only on a glucose+fructose blend.

Separately on dose: the biggest performance gain was seen with an intake of 60–80 g of carbs per hour. And a caveat just in case: if you're moving along the course at very low intensity, carbohydrate oxidation drops, and the numbers should be adjusted downward.

How to train the gut

The gut's transporters are trainable. If you regularly eat plenty of carbs (including in training), their number grows, and on the same nutrition you oxidize more "external" carbs. The gut is just as adaptable a system as the heart or the muscles.

Typical beginner mistakes:

trying maximum fueling for the first time on race day — a guaranteed GI revolt;
sitting on "pure" glucose and running into 60 g/h, puzzled about why it won't go;
swallowing concentrated gels without water in the heat — absorption drops even further.

How to apply it in practice

Count by time, not by distance. Estimate the duration of the start and pick the range: 60 g/h up to three hours, toward 90 g/h on ultra-long events.
Check the composition. The label should list both glucose (maltodextrin) and fructose in a ratio of about 2:1. Without fructose you can't get above 60 g/h.
Train your stomach in advance. On long workouts, rehearse exactly the nutrition scheme you plan for the race — by grams and by timing.
Build up gradually — from 60 to 80–90 g/h over several weeks, not in a single go.
Don't forget water. Concentrated carbs demand fluid, otherwise absorption stalls.

The bottom line

A single source (glucose) = a ceiling of ~60 g/h because of the SGLT1 transporter limit.
A glucose+fructose blend (2:1) raises absorption to ~90 g/h (up to 1.26 g/min, +75%).
Dose by duration: < 45–60 min, a mouth rinse is enough; 2–3 h, up to 60 g/h; ultra-long, up to 90 g/h.
The biggest performance gain comes at 60–80 g/h.
The gut is trainable: rehearse nutrition in training and build up volume in advance.
The absorption rate does not depend on weight and depends little on the sport or level.

Source: Jeukendrup — Carbohydrate intake during exercise. https://pmc.ncbi.nlm.nih.gov/articles/PMC4008807/