Ten to twenty years ago, most runners were told to take one gel an hour and “don’t upset your stomach.” On paper that’s roughly 30–60 g of carbohydrate per hour and it mapped onto the old idea that the gut was the limiting factor, so conservative fueling felt safer.
Fast-forward to today and the picture is very different. At the sharp end of the sport, elites aim for 90–120+ g of carbohydrate per hour in long events, and plenty of sub-elites are following with great success. What changed? In short: better science, better products, and a new mindset. Research shows that when you use multiple transportable carbohydrates (glucose + fructose), you can increase absorption and oxidation beyond the old 60 g/h ceiling, pushing toward ~1.5–1.8 g/min (~90–108 g/h) and, for some, even higher—with performance benefits and fewer GI issues when practiced. Gatorade Sports Science Institute+1
Below, we’ll break down where we were vs where we are, how fueling changes performance, and how to actually train your gut to handle higher intakes.
1) From “one gel an hour” to 90–120 g/h
Then (c. 2005–2015): Common guidance for endurance events was ~30–60 g/h. That limit largely reflected the capacity of the SGLT1 glucose transporter in the small intestine. Feed only glucose (or maltodextrin) and you’ll saturate SGLT1; push harder and unabsorbed carbs linger in the gut → sloshing, cramps, bathroom stops. Taylor & Francis Online
Now: Mix glucose + fructose (which uses a different transporter, GLUT5) and you open a second “door” into the bloodstream, increasing exogenous carbohydrate oxidation rates and delaying fatigue. That’s the basis for modern guidance: ~90 g/h for events ≥2.5–3 h, with many athletes tolerating 100–120 g/h when well trained. World Athletics’ ultra review explicitly summarizes ~90 g/h as a target for long runs and racing; applied lab work and field practice show the feasibility of going higher for some athletes. worldathletics.org+1
A recent lab study in highly trained endurance athletes even compared 120 g/h (fructose:glucose ≈ 0.8:1) vs 90 g/h (1:2) during a 3-h session. The higher intake boosted exogenous carb oxidation, supporting the idea that >90 g/h can be useful when gut-trained and logistically manageable. (Important: more is not automatically better—individual tolerance matters.) SpringerLink
Takeaway: The old ceiling was about single-sugar transport. The new ceiling reflects dual-transporter fueling, athlete-specific tolerance, and practice.
2) Why fueling this way feels (and is) faster
Carb availability governs pace. Ultras are mostly aerobic, but when you climb, surge, or just try to hold form late, you lean on carbohydrate. Keep a steady stream of carbs coming in and you spare glycogen, maintain higher power/pace, and reduce the depth of the late-race fade.
The brain runs better on fuel. Like it or not, ultras are cognitive. Technical descents, route choices, and nutrition/hydration decisions all degrade when blood glucose dips. Smoother, frequent fueling stabilizes cognition and helps you make better decisions when tired.
GI comfort is trainable. Many GI problems aren’t “bad luck”, they’re mismatch problems: intake too high for your current transporter capacity, too concentrated relative to fluid/sodium, or too “new” for race stress. With structured practice, the GI tract adapts—transporter expression, gastric emptying, and symptom tolerance all improve. Gatorade Sports Science Institute
Bottom line: Fueling isn’t a lifeline for when things go wrong; it is a performance strategy.
3) How to increase tolerance and gut-train (practical plan)
The gut adapts to the demands you place on it. Here’s a runner-friendly progression we use at Hungry Runner.
Step A — Set your starting point
- If you’ve been living at ~40–50 g/h, start by proving you can hit 60 g/h comfortably on a steady long run or race-pace session.
- Choose glucose + fructose products (look for blends, e.g., maltodextrin + fructose; many modern gels/drinks are ~2:1 or 1:0.8). Gatorade Sports Science Institute
Step B — Build gradually (over 6–8 weeks)
- Weeks 1–2: Long run at easy-moderate intensity. Fuel 60 g/h (e.g., one 30 g gel every 30 min) + chase each carb intake with a few mouthfuls of water.
- Weeks 3–4: Move to 75 g/h. Consider adding a carb drink so you’re not relying solely on gels. Keep flavors simple; rotating textures helps.
- Weeks 5–6: Aim for 90 g/h on at least one long run and one steady race-pace workout. Note any symptom patterns (timing, intensity, terrain).
- Weeks 7–8: If 90 g/h feels good, test 100–110 g/h during a long run with segments close to expected race intensity. Only go higher if your stomach stays quiet and your performance feels stable.
Evidence check: A two-week “gut-training” protocol with regular, deliberate high-carb intakes in training has been shown to improve GI comfort, raise blood glucose availability, and improve running performance outcomes vs untrained guts. Translation: practice works. SciSpace
Step C — Get the concentration and fluids right
- Your total carb per hour is only part of the equation; solution concentration (% carbs) matters for gastric emptying.
- As a rule of thumb, keep most fluids ~6–12% carbs (that’s 60–120 g per liter). If you’re stacking gels on top of plain water, the effective concentration in your stomach can spike—so sip water with gels rather than dumping them all at once.
- Sodium helps with fluid absorption and reduces the risk of “sloshing.” Match your plan to the weather and your sweat rate.
Step D — Fuel early, then steady
- Take your first gel/drink within 20–30 min from the start (you’re not waiting until you’re empty; you’re keeping the tank topped up). Then feed every 10–20 min in small, predictable doses. Steady beats sporadic.
Step E — Rehearse race fuels exactly
- Use the brand and flavors you’ll race with. Add in the exact caffeine timing you plan to use.
- Logistics: where will the bottles/gels be? What’s in each flask? Label them. If drop bags/crew are allowed, pre-portion by hour.
Step F — Learn your red and green flags
- Green flags: stable stomach pressure, no burping/bloating between intakes, able to take small sips/bites at planned intervals, steady energy and mood.
- Red flags: sharp cramps, rising nausea after intakes (especially on downhills), sudden aversion to sweetness, or mental fog despite fueling (could indicate dehydration, mis-timed caffeine, or under-salting).
If red flags show up, ease down to the last comfortable rate (e.g., 90 g/h), switch format (drink → gel or vice versa), add a small sodium/water push, and resume smaller, more frequent sips. Practice these “resets” in training so they’re automatic on race day.
4) What about “real food”?
Real foods (bananas, rice balls, soft bars) can work well if they’re low fiber, low fat, and low protein during the running segment (save the savory/fatty items for walk breaks or aid station pauses). A recent narrative review notes that food-first strategies can perform comparably when carb delivery is matched and logistics are dialed in; the trade-off is precision and portability. For high intakes (≥90 g/h), drinks + gels are simply the easiest way to hit targets without overfilling the stomach. MDPI
5) A simple template you can copy
- Target: 90–110 g/h (after gut-training), composed of glucose + fructose.
- Structure: split hourly carbs into 6–8 mini-doses (every 7–10 min) rather than big hits every 30–40 min.
- Formats: e.g., one 500 ml bottle at ~60–70 g + two 30 g gels per hour; or two 500 ml bottles at ~40–50 g each per hour; or one bottle + chews/gels.
- Hydration: adjust to conditions and sweat rate
- Caffeine: if you use it, time small doses strategically (e.g., late climbs, overnight sections) and rehearse exactly in training.
6) Mindset shift: fueling is training
The biggest change in ultrarunning nutrition isn’t the products it’s the mindset. We used to hope the gel would sit well; now we train our GI tract so race day feels routine. We used to treat fueling as “insurance”; now we recognize it as a way to maintain speed, preserve form, cognition, and mood.
If you’re stuck at 40–60 g/h because “my stomach can’t handle more,” that’s not a verdict it’s a training plan. Start conservative, build weekly, mix your carb sources, reset quickly if symptoms arise, and keep notes. Give yourself 6–8 weeks and you’ll be surprised how different your long runs feel.
⭐ 8-Week Gut-Training Plan
(Recommended for runners targeting 90–110 g/h in 50–100 km events)
| Week | Long Run Fuel Target | Structure | Focus |
|---|---|---|---|
| 1 | 60 g/h | 30 g every 30 min | Basic tolerance |
| 2 | 60–70 g/h | Add carb drink | Check sweetness + texture preferences |
| 3 | 75 g/h | 25 g every 20 min | Practice fueling on climbs |
| 4 | 75–85 g/h | Include gels + drink mix | Sodium timing test |
| 5 | 90 g/h | 20 g every 13–15 min | One session with race pace efforts |
| 6 | 90–100 g/h | Add caffeine trial | GI response in heat |
| 7 | 100–110 g/h | Mix liquids + solids | Aid station simulation |
| 8 | 90–110 g/h | Race rehearsal | Nail logistics + confidence |
Sources and further reading
- Jeukendrup AE. Multiple transportable carbohydrates improve absorption and performance; guidance for ~90 g/h in long events. (GSSI Sports Science Exchange; review + mechanisms). Gatorade Sports Science Institute
- Jeukendrup & colleagues (various reviews). Multiple transportable carbs raise exogenous oxidation above single-glucose limits; practical race recommendations. Taylor & Francis Online
- World Athletics (Costa et al., 2019). Nutrition for Ultramarathon Running—review recommending ~90 g/h for ≥3 h events and discussing logistics/tolerability in ultras. worldathletics.org
- Podlogar & Wallis (2022). Contemporary perspectives on carbohydrate for endurance athletes; context for higher intakes and individualization. University of Birmingham
- Costa et al. (2017). Two-week gut-training study: improved GI comfort, glucose availability, and running outcomes when practicing higher intakes. SciSpace
- König et al. (2022). 120 g/h vs 90 g/h comparison in trained endurance athletes; higher exogenous carb oxidation at 120 g/h with fructose-rich mix. SpringerLink
