Lab studies say you can absorb 90 to 120 grams of carbohydrate an hour. Real riders in real ultra-endurance events eat less than half that. One field study of a 120-kilometer ultramarathon found hourly carbohydrate intake averaging just 46.7 grams. Two of the five runners tracked never reached 60 grams an hour.
That gap between the lab ceiling and what happens on course is the real problem in a 200-mile gravel race. Unbound Gravel makes it physical: the course has exactly two checkpoints where a crew may legally meet you. Everywhere else, you carry what you eat. This piece runs the aid-station math on what you must pack, and builds a fueling protocol for hour 12, not hour 2 of a lab trial.
Why the 90 g/h Rule Wasn’t Built for a 12-Hour Race
The 90-to-120 gram figure comes from real research, but it’s measured in a narrow window. A single carb source, like glucose alone, tops out around 60 grams an hour. It saturates one gut transporter (SGLT1). Add fructose, which uses a separate transporter (GLUT5), and your gut can absorb more at once. That’s why sports drinks blend two sugars instead of one.
A 2022 trial pushed this further. Cyclists fed 120 grams an hour at a higher-fructose ratio oxidized more carbohydrate than cyclists fed 90 grams an hour at a glucose-heavy ratio (Podlogar et al., 2022). Translation: the right blend lets your gut process more fuel, faster.
Here’s the catch. That trial ran about three hours, in a lab, on a strict feeding schedule. Unbound’s mid-pack finishers are out 12 to 17 hours, in heat, on washboard gravel. Lab conditions and race-day conditions aren’t the same test.
Field data backs this up. Tracking five runners through a 120-kilometer ultramarathon, hourly intake ranged from 22.1 to 62.6 grams, averaging 46.7 (Wardenaar et al., 2018). Nobody hit the lab ceiling.
Plan for the gap. Not the ceiling.
The Aid-Station Math: What Unbound’s Checkpoints Force You to Carry
Unbound Gravel 200 has two legal support checkpoints: mile 70, in Alma, Kansas, and mile 148, in Council Grove. Outside those two points, support vehicles are banned from the course entirely. Get caught with one and you’re disqualified.
That rule creates three unsupported stretches. Seventy miles to Checkpoint 1, a brutal 78 miles between the two checkpoints, and roughly 55 miles to the finish. Nearly a third of the race with zero resupply.
Here’s what that means in grams you have to pack. These numbers are calculated for this article, not a cited study result. Treat them as planning math, not gospel.
| Segment | Distance | Time @ 10 mph | Time @ 12 mph | Time @ 14 mph | Carbs @ 60 g/h | Carbs @ 90 g/h |
|---|---|---|---|---|---|---|
| Start to Checkpoint 1 (Alma, mi 70) | 70 mi | 7:00 | 5:50 | 5:00 | 420 g | 630 g |
| Checkpoint 1 to Checkpoint 2 (Council Grove, mi 148) | 78 mi | 7:48 | 6:30 | 5:34 | 468 g | 702 g |
| Checkpoint 2 to Finish | ~54.5 mi | 5:27 | 4:33 | 3:54 | 327 g | 490 g |
Calculated from Unbound’s official checkpoint mileage and standard carbohydrate guidance — illustrative planning math, not a cited research result. Real pace varies with fitness, wind, and mud.
Translation: on the 78-mile middle stretch, a mid-pack rider fueling at just 60 grams an hour needs roughly 470 grams of carbohydrate packed before a single gel gets opened. That’s about nine or ten gels, or the equivalent in chews and rice cakes, on top of water and sodium. Distance and pace in, grams out.
The Solid-to-Liquid Switch: A Protocol, Not a Vibe
Here’s a common myth: switching to solid food late in a race gets you more usable fuel. It doesn’t. A 2022 tracer study fed cyclists 120 grams an hour as fluid, gel, or chew and found no meaningful difference in how much got oxidized. Your gut absorbs sugar the same way no matter what container it arrives in.
So why switch formats at all? Behavior, not biology. Riders who eat only sweet gels for ten hours stop wanting to eat them, and a rider who stops eating starts losing power fast. The fix isn’t a better gel. It’s rotating formats before you get sick of the one you’re on.
There’s a real tradeoff, too. Liquids empty fast, around 1 to 1.2 liters an hour, versus roughly 200 to 300 grams an hour for solids (a rule of thumb, not one clean study). Load up on solids while chugging water for heat, and you can back up your own gut.
Bars deserve extra caution. One trial found solid bars caused more nausea and cramping than gels or drinks at a matched dose, with a likely power cost (Guillochon & Rowlands, 2017).
| Format | Approx. gastric emptying | GI comfort at matched dose | Best window |
|---|---|---|---|
| Liquid drink mix | ~1.0-1.2 L/hour (rule of thumb) | Best tolerated | Hours 0-12, the backbone |
| Gel or chew | Dissolves and empties like a liquid | Comparable to liquid | Hours 0-6, sweet phase |
| Real food (rice cakes, potatoes, pretzels) | ~200-300 g/hour (same rule-of-thumb range) | Good once introduced before flavor fatigue peaks | Hours 4-10, savory rotation |
| Bars | Same slow solid-emptying range | Worse: more nausea, fullness, cramping | Use sparingly, early only |
Gastric emptying figures are a widely repeated sports-nutrition rule of thumb, not a single controlled study. Treat as directional.
A workable protocol: run liquid carbs and gels as your backbone all race. Add chews and real food around hour three or four. Save salty solids like potatoes, pretzels, and rice cakes for the second half. Keep a bar in reserve, not as a staple.
Flavor Fatigue and the Sweet-to-Savory Rotation
Ever crave a pretzel at hour six, even with a pocket full of gels? That’s flavor fatigue, a documented food-science phenomenon called sensory-specific satiety. Your appetite for one flavor drops the more you eat it, even while your body still needs the calories.
Think of it like eating birthday cake for breakfast, lunch, and dinner. By the third slice, you’re not hungry for cake. You’re hungry for literally anything else.
Some sources report a pattern: athletes prefer sweet food early, then crave salty or savory options later (Precision Hydration, citing an unverified 2021 study). Treat that 60-minute mark as a loose signal, not a stopwatch. Timing varies rider to rider.
The fix: build variety in from the start. Pack at least one savory option before you ever feel sick of sweet. By the time flavor fatigue hits, the alternative should already be in your pocket.
GI Distress and Gut Training: Lowering the Odds Before Race Day
Stomach trouble ends more long races than injuries do. Studies report GI symptoms in roughly 30 to 56% of distance athletes. Some ultra-running studies cite figures as high as 90% (Ryan et al., 2023). Be careful with that high end. It comes almost entirely from running research, where impact stresses the gut more than cycling does.
The good news: GI tolerance is trainable, the same way your legs adapt to load. In one controlled study, runners repeated a daily carbohydrate-feeding challenge for two weeks. They cut GI symptoms by 60 to 63%, whether the carbs came from gel or whole food (Miall et al., 2018). A separate review found repetitive feeding cut malabsorption by 45 to 54%.
The fastest fix for a fragile race-day stomach isn’t a new supplement. It’s rehearsal.
Gut training with 120 grams of carbs an hour walks through the progression, and gut training for endurance athletes covers the broader principle. Heat adds risk, too. The blood-flow mechanism behind heat-induced GI distress explains why hot afternoons make things worse.
Sodium in the Unsupported Gap
Carbohydrate isn’t the only thing you’re rationing between checkpoints. Sodium losses vary enormously between riders. Baseline guidance runs 300 to 600 milligrams an hour, but documented heavy sweaters can lose 2,500 milligrams or more in that same hour. A generic electrolyte dose can leave a heavy sweater badly short by mile 100.
That’s a problem you can’t fix at a checkpoint 78 miles away. Know your own number before race day, then carry a personalized dose. Sodium needs for heavy sweaters shows how to estimate yours, and thirst-driven vs. programmed hydration covers pairing sodium with what you drink.
What This Looks Like for One Rider
Take a rider I’ll call Dave. He’s 44, on his third Unbound 200, averaging around 12 mph on the gravel sections. In 2023, he fueled by feel, ran empty near mile 130, and lost 40 minutes scavenging at a gas station outside Council Grove.
In 2024, he ran the aid-station math first. He packed 640 grams of carbohydrate for the 78-mile middle stretch, half liquid and gel, half chews and salted rice cakes, plus sodium at 700 milligrams an hour. He finished 52 minutes faster. No bonk, no gas station detour, no stomach issues after mile 150.
Building Your Own Aid-Station Math
None of this math is gravel-specific. Any self-supported endurance event asks the same question. How many hours between resupply, and how many grams do you need to survive them? A long-course triathlete’s bike leg and an ultramarathoner’s mountain aid gap run on the same formula. Distance, pace, and target grams per hour, minus what’s in your pocket.
AthleteOS’s fueling calculator runs this math for you. Instead of a flat 90 g/h default lifted from a lab protocol, it scales your carb target to your real race duration and checkpoint gaps. If you’ve bonked before and never known why, why you hit the wall at mile 20 is worth reading next. Build your own race fueling plan before your next start line.