If you’ve spent any time in a running or cycling forum, you’ve seen the debate: some athletes swear by a gel every 45 minutes, others are necking carb drink mixes that add up to 90 grams of carbohydrate an hour. As a dietitian who works with endurance athletes, the question I get most on this topic isn’t "what should I eat" — it’s "how much, per hour, actually matters?" The honest answer is that the number is higher than most recreational athletes assume, and the ceiling on how much your body can use has moved in the last decade.
The General Range: 30 to 90 Grams Per Hour
For any continuous exercise lasting longer than about an hour, general sports nutrition guidance puts carbohydrate intake somewhere between 30 and 60 grams per hour. Once you’re out past the two-hour mark — which covers most marathoners, century-ride cyclists, and every triathlon bike or run leg of consequence — that range commonly extends up toward 90 grams per hour, particularly for ultra-endurance efforts. A useful rule of thumb some clinicians use is roughly 0.7 grams of carbohydrate per kilogram of bodyweight per hour, which lands most adult athletes in a similar 45–75 gram range depending on size. None of these numbers are a hard prescription — they’re a starting range to test in training, not on race day.
Why the Old "60 Gram Ceiling" No Longer Holds
For years, the working assumption in sports nutrition was that the body could only oxidize — actually burn for fuel — about 60 grams of carbohydrate per hour, no matter how much you ate. That ceiling exists because a single type of sugar, glucose, is absorbed through one intestinal transporter (called SGLT1), and that transporter saturates. Eat past it and the extra sugar just sits in your gut, which is exactly how athletes end up with cramping, bloating, or a mid-race bathroom emergency.
What changed the picture is research into multiple transportable carbohydrates — specifically, combining glucose with fructose. Fructose is absorbed through a separate transporter (GLUT5), so when you pair the two sugar types, you’re effectively opening a second lane of traffic instead of overloading one. That’s the mechanism behind the higher 90-gram-per-hour targets you now see on many commercial gels, chews, and drink mixes that list both "glucose" (or dextrose/maltodextrin) and fructose on the label — it isn’t marketing, it’s how the gut actually absorbs more fuel per hour without the GI distress that plain glucose-only products tend to cause at higher doses.
Running, Cycling, and Triathlon: Does the Sport Change the Number?
The carbohydrate-per-hour target itself doesn’t fundamentally shift between running and cycling, but tolerance often does. Running jostles the gut in a way cycling doesn’t, so many athletes who can comfortably handle 80–90 grams an hour on the bike find they need to dial back on the run — which matters directly for triathletes moving from one discipline to the next in the same race. A practical pattern I see work well:
| Event type | Typical duration | Reasonable starting target |
|---|---|---|
| Easy long run or ride under 75 minutes | <75 min | Often none needed — water is enough |
| Marathon, half-Ironman run, long training run | 90 min–3.5 hrs | 45–75 g/hour, building toward the top of that range if tolerated |
| Long cycling event, Ironman bike leg | 3+ hrs | 75–90 g/hour using a glucose:fructose blend |
| Ultra-distance running or multi-hour efforts | 4+ hrs | Up to ~90 g/hour, split into small, frequent doses |
Gut Training: The Piece Most Athletes Skip
The single biggest reason athletes fail to hit these targets isn’t a lack of product on the shelf — it’s an untrained gut. Regularly practicing carbohydrate intake during training sessions appears to upregulate those same intestinal transporters over time, meaning the gut genuinely adapts to empty faster, absorb more, and tolerate a larger volume of fuel with fewer symptoms. This is why "gut training" has become as standard a part of race preparation as tapering mileage: athletes deliberately practice their exact race-day fueling plan — same products, same timing, same volume — in training long before it matters, especially for anything lasting more than about 90 minutes. Discovering on race morning that 60 grams an hour leaves you nauseated is a lesson better learned on a Tuesday long run than at mile 18.
Building Your Own Number
Rather than copying a number off a label, treat your carbs-per-hour target as something you test and refine over several weeks:
- Start conservative. Begin around 30–45 grams per hour on a long training session and note how your stomach handles it.
- Add gradually. Increase by roughly 10–15 grams per hour every couple of sessions rather than jumping straight to 90.
- Choose a glucose:fructose product once you’re above ~60 g/hour. A single-sugar source is far more likely to cause GI upset once you’re past the old ceiling.
- Practice the exact race plan. Same brand, same flavor, same interval — rehearsed, not improvised.
- Track how you feel, not just the math. Energy levels, focus, and gut comfort in the final third of a long session tell you more than the total grams consumed.
There’s no universal "right" number of carbs per hour — there’s a right number for your event length, your sport, and a gut you’ve actually trained to handle it. Start conservatively, build deliberately, and treat every long training session between now and race day as a rehearsal for exactly what’s going in your hand, and your stomach, when it counts. Get that number right in training, and race-day fuelling stops being a gamble and becomes just another rehearsed part of the plan.