One hundred and twenty grams per hour. That's what the best-fuelled riders in the World Tour are absorbing on race day — and if you tried that tomorrow, you'd probably be sick in a hedge by kilometre 60.
The difference isn't genetics. It's training. Asker Jeukendrup's research showed that the gut adapts to carbohydrate exposure the same way legs adapt to intervals — progressively, measurably, over four to six weeks. The intestinal transporters that move sugar from your gut into your bloodstream literally increase in density when you ask them to work harder. Your gut has a speed limit, but that limit is trainable.
Right now, most amateur cyclists can absorb 40, maybe 50 grams per hour. Their legs are burning 90-plus. That gap is the single biggest fuelling limiter on any long ride — and it's completely fixable.
The Science: Why Your Gut Has a Speed Limit
The physiology matters here. Once you understand why there is a limit, the solution becomes obvious.
When you eat or drink carbohydrate during exercise, it arrives in your small intestine and needs to cross the intestinal wall to get into your bloodstream. That crossing happens through specific transport proteins — think of them as doors in the intestinal wall that let sugar molecules through.
For glucose, the transporter is called SGLT1. It sits in the lining of your small intestine and it actively pumps glucose from the gut into the blood. But here is the critical point — SGLT1 has a maximum capacity. No matter how much glucose you pour into your stomach, SGLT1 can only move roughly 60 grams per hour across the intestinal wall. That is the ceiling. Dump 90 grams of glucose in there and 30 grams just sits in your gut, pulling water into the intestine, creating bloating, nausea, and the kind of GI distress that ends long rides.
This is why the old sports nutrition advice capped carbohydrate intake at 60g per hour. With glucose alone, that was actually the maximum.
Then Asker Jeukendrup changed everything.
Jeukendrup and the Dual-Transport Breakthrough
Asker Jeukendrup, working out of the University of Birmingham and later Loughborough, was the researcher who cracked the absorption ceiling. His work through the 2000s and into the 2010s showed something that fundamentally changed endurance nutrition.
Fructose uses a completely different transporter. It crosses the intestinal wall through GLUT5, which is a separate pathway from the SGLT1 that handles glucose. Two different doors. Two different queues. No competition between them.
When you combine glucose and fructose in the right ratio, you activate both transport systems simultaneously. SGLT1 handles the glucose at up to 60g per hour. GLUT5 handles the fructose at up to 30-40g per hour. Total absorption: 90-100g per hour. In well-trained guts with optimised protocols, some riders push past 120g per hour.
The original recommendation from Jeukendrup's research was a 2:1 glucose-to-fructose ratio. Two parts glucose for every one part fructose. More recent work, including data from teams working with riders like Tadej Pogacar, suggests a ratio closer to 1:0.8 may be even more effective — nearly equal parts glucose and fructose, which gets more total carbohydrate through the system per hour.
This is not theory. This is the foundation of every modern sports nutrition product on the market. When you see "dual-source carbohydrate" or "glucose-fructose blend" or "multiple transportable carbohydrates" on a label, that is Jeukendrup's research being applied.
But Here Is the Part Most People Miss
Having the right fuel is only half the equation. Your gut has to be trained to handle it.
An untrained gut — one that has never practised absorbing high carbohydrate loads during exercise — will revolt at 90g per hour. Nausea, bloating, cramps, diarrhoea. The GI distress is real, and it is the reason most amateur cyclists stay well below their potential fuelling rate. They tried 80g per hour once, felt terrible, and concluded they "just can't tolerate that much."
They can. They just have not trained for it.
Cox et al. published a landmark study in 2010 that demonstrated gut training is measurable and repeatable. They took a group of athletes and had them consume high amounts of carbohydrate during exercise every day for 28 days. At the end of those 28 days, the rate of exogenous carbohydrate oxidation — the amount of ingested carbohydrate the body was actually burning as fuel — had significantly increased. The gut had adapted.
What happens during gut training is a process called transporter upregulation. When you repeatedly expose your intestinal lining to carbohydrate during exercise, the cells respond by producing more SGLT1 and GLUT5 transporters. More doors in the wall. More capacity to move sugar through. Jeukendrup's 2010 review paper laid this out clearly — the gut responds to the demand placed on it, just like muscle fibres respond to training load.
Gastric emptying speeds up too. Your stomach learns to pass food through to the small intestine faster. And the gut's tolerance to the osmotic stress of concentrated carbohydrate solutions improves, meaning fewer symptoms even at high intake rates.
This is exactly the same principle as progressive overload in training. You would not try to ride your first 200km event without building up to it. Your gut deserves the same respect.
The Practical Protocol: Week by Week
This is the part that matters. Here is how you actually do it.
Weeks 1-2: Establish your baseline. On your long rides — anything over 90 minutes — start fuelling at 30-40g of carbohydrate per hour. This is deliberately conservative. If you have not been fuelling much during rides, even 30g per hour might feel like a lot. Use a glucose-fructose product from the start, even at this low dose. You want your gut adapting to the dual-transport system from day one. A single energy gel plus a few sips of a carbohydrate drink will get you to 30-40g per hour easily.
Weeks 3-4: Build to 50-60g per hour. Add another gel or increase the concentration of your drink mix. The total target is 50-60g per hour on every long ride. You should be practising this at least twice per week — your weekend long ride and one midweek session of 90 minutes or more. Pay attention to how your stomach feels. Mild bloating is normal and acceptable. Nausea that stops you eating or forces you to back off the pace means you have gone too far too fast. Drop back by 10g per hour and hold for another week.
Weeks 5-6: Push to 70-80g per hour. This is where it starts to feel like real fuelling. Two gels per hour plus a carbohydrate drink, or three gels per hour if you prefer plain water. You are now moving past the glucose-only ceiling, and the fructose pathway is doing meaningful work. Your gut should be adapting. GI symptoms should be noticeably less than they would have been if you had jumped straight to this intake.
Weeks 7-8: Target 80-100g per hour. For most age-group cyclists, 80-90g per hour is the practical sweet spot. It is enough fuel to sustain hard efforts for five or six hours without bonking, and it is within the absorption capacity of a gut that has been through four to six weeks of progressive training. Some riders will push to 100g per hour with no issues. Others will find their ceiling at 80g. Both are massive improvements over the 30-40g most amateurs start with.
Beyond Week 8: If you are targeting 100-120g per hour — which is truly necessary for ultra-distance events or multi-day racing — keep building gradually. Add 5-10g per hour per week. Test at race intensity, not just easy endurance pace. The gut behaves differently at threshold than it does at zone 2 because blood flow is redirected away from the digestive system during hard efforts.
What to Actually Eat and Drink
The specific products matter less than the glucose-fructose ratio and the total amount. But let me give you practical options.
Commercial sports nutrition products. Most modern gels and drink mixes already use glucose-fructose blends. Check the label. You want maltodextrin or glucose listed alongside fructose. Brands like Maurten, SiS Beta Fuel, and Precision Fuel all use the dual-transport system. The convenience is worth the cost if you are racing seriously.
Homemade drink mix. You can make your own. Maltodextrin powder (glucose source) and fructose powder, mixed in a 2:1 or 1:0.8 ratio. Dissolve 60-80g of the mix into a 500ml bottle. Add a pinch of salt. It will not taste as refined as a commercial product but it does the same job at a fraction of the price. When I had Dr. David Dunne on the podcast, he was clear that the science does not care about the branding. The transporters care about the molecules.
Real food. Rice cakes with jam. Bananas. Fig rolls. Dates. These all contain a mix of glucose and fructose in varying ratios. They work perfectly well for steady-state rides. The limitation is at very high intake rates and high intensities — real food is harder to chew, slower to digest, and more likely to cause GI issues than engineered products when you are riding at threshold. For racing, gels and drink mixes are more practical. For long training rides, real food is fine and arguably better for gut training because it challenges the full digestive process.
The late-race cola. Flat cola is about 55% glucose and 45% fructose — almost exactly the ratio you want. It also has caffeine. There is a reason it has been a pro peloton staple for decades.
Why GI Distress Happens and How to Minimise It
GI distress during exercise is not random bad luck. It has specific, identifiable causes, and every one of them is fixable.
Concentration too high. If your drink mix is too concentrated — too much sugar in too little water — it creates a hypertonic solution in your stomach. Water gets pulled into the gut by osmosis instead of being absorbed into the blood. Result: bloating, nausea, and sometimes diarrhoea. Keep your drink mix to 6-8% carbohydrate concentration for bottles you are sipping regularly. That is roughly 30-40g of carbohydrate per 500ml.
Fibre, fat, and protein too close to riding. All three slow gastric emptying. A high-fibre breakfast two hours before a race means food is still sitting in your stomach when you start fuelling on the bike. Keep your pre-ride meal low in fibre, low in fat, moderate in protein. White rice, white toast with honey, a banana. Nothing adventurous.
Dehydration. When you are dehydrated, blood flow to the gut drops as the body prioritises the muscles and skin. Less blood flow means slower absorption and a higher risk of GI symptoms. Drink to your thirst and start your ride well hydrated.
Too much too soon. This is the most common one. Jumping from zero on-bike nutrition to 80g per hour because you read an article about what the pros do. Your gut has not adapted. The transporters have not upregulated. Progressive overload. Start low. Build up. Be patient.
Intensity. At high intensities — above about 80% of VO2max — blood is shunted away from the gut to the working muscles. Absorption capacity drops. This is why you practise fuelling at race intensity, not just on easy endurance rides. Your gut needs to learn to function when blood flow is compromised.
The Training Ride Is Your Lab
Every long ride is an opportunity to train your gut. This is not something you do separately. It is something you build into the rides you are already doing.
Use the same products you plan to race with. Every time. If you race with Maurten gels, train with Maurten gels. If you race with a homemade drink mix, train with that exact recipe. Your gut adapts to specific foods and specific concentrations. Race day should never be the first time your gut encounters your fuel plan.
Practise at race intensity, not just at easy pace. Do your fuelling practice during tempo blocks and sweet spot intervals — sessions that simulate the metabolic demands of competition. Easy zone 2 rides build baseline tolerance, but they do not replicate the gut stress of racing.
Keep a simple log. Write down what you consumed, how many grams per hour, and how your gut felt on a scale of 1 to 5. After four to six weeks, you will have clear data on what works, what causes problems, and where your current ceiling sits. No guesswork. Just information.
The Numbers That Matter
Let me put this in perspective with some concrete figures.
A rider absorbing 40g of carbohydrate per hour over a five-hour sportive takes in 200g of exogenous fuel. A rider absorbing 90g per hour takes in 450g. That is 250 additional grams of carbohydrate — a thousand extra calories — reaching the working muscles. Less fade in the final two hours. Better power on the late climbs. Clearer thinking in the finale.
This is not marginal. This is the difference between surviving a long event and performing in it.
Professor Stephen Seiler has talked about the importance of fatigue resistance — the ability to maintain output as the hours pass. Fuelling is the single biggest lever you have for fatigue resistance in events over three hours. You can have the best engine in the field, but if you cannot feed it, it runs out of fuel like everyone else's.
Your Gut Is Trainable. Start This Week.
The science is settled. Jeukendrup's research, Cox et al. 2010, and over a decade of real-world application in the World Tour have proven that the gut adapts to carbohydrate demand during exercise. The transporters upregulate. Gastric emptying speeds up. GI tolerance improves.
The protocol is simple. Start where you are. Add 10g per hour every one to two weeks. Use glucose-fructose products from the beginning. Practise on training rides at race intensity. Be patient.
If you build from 30-40g per hour to 80-90g per hour over the next two months, you will notice the difference on every ride over three hours. Less bonking. More power in the final quarter. Better recovery because you did not deplete your glycogen stores to zero.
Your gut adapts like your legs, your lungs, your cardiovascular system. The only question is whether you train it deliberately or leave it as the weakest link in your performance chain.
If you want help building a complete fuelling plan — gut training, race-day nutrition, the whole system — that is exactly what we work on inside the community. Come join us at Roadman Cycling on Skool and stop leaving fuel on the table.