Three hours into a sportive, the rider next to you stops pedalling. Sits up. Reaches into an empty back pocket. You know the look — hollow eyes, chalk-white face, legs that have simply switched off. The bonk. And the cause, in almost every case, is not fitness. It is fuel. Specifically, the fuel that was not eaten in the first two hours while the legs still felt fine.
I have watched this pattern repeat across hundreds of riders in our Roadman Cycling community, and after 1,400-plus podcast episodes with sports nutritionists, World Tour dietitians, and exercise physiologists, the data is clear: the single largest performance gain available to most amateur cyclists is not a new interval protocol. It is eating enough on race day.
This cycling nutrition guide covers everything — the science of carbohydrate delivery, the practical protocols for building a fuelling plan, gut training timelines, and worked examples for a four-hour sportive and a six-hour gran fondo. If you want personalised numbers based on your weight, ride duration, and intensity, run them through the Fuel Planner alongside this article. And if you want a quick diagnostic on where your current fuelling practices fall short before diving in, start with the Fuelling Self-Assessment.
Why Most Amateurs Bonk
The maths is brutal. At moderate race intensity (65-80% FTP), your muscles burn between 60 and 90 grams of carbohydrate per hour. Your body stores roughly 400-500g of glycogen across muscle and liver. Without eating, that store is empty somewhere between hour three and hour four — sooner if you started with a half-filled tank because you skipped breakfast or ate nervously.
Most amateur cyclists eat 20-40g of carbohydrate per hour during racing. A single gel every 45 minutes. Half a banana here and there. That is a deficit of 40-60g per hour against what the muscles are burning. By hour three, you are running on fumes.
The cruel part is that the bonk does not arrive gradually. Glycogen depletion follows a cliff, not a slope. You feel strong at 30% glycogen, acceptable at 20%, and then the lights go out. By the time your legs fail, dietary intervention is too late — the gut cannot absorb carbohydrate fast enough to rescue the situation. The fix is not better rescue strategy. It is never reaching that cliff in the first place.
The 60-90g Per Hour Target and the Science Behind It
The research on carbohydrate oxidation during exercise comes overwhelmingly from the work of Asker Jeukendrup, whose lab established the framework that every sports nutritionist now uses. The key findings are worth knowing because they explain why your fuelling strategy must be designed around transport biology, not just appetite.
The glucose ceiling
Glucose is absorbed through the intestinal wall via a transporter called SGLT1. This transporter has a fixed capacity — roughly 60g per hour, regardless of how much glucose you consume. Eat 80g of glucose-only product per hour, and 20g of it sits in the gut causing bloating, nausea, and cramping. This is why so many riders conclude they have a "sensitive stomach" when they actually have a transport bottleneck.
The fructose pathway
Fructose uses a completely different transporter: GLUT5. By consuming glucose and fructose together — the so-called multiple transportable carbohydrates approach — you run both transporters in parallel. The original research suggested a 2:1 glucose-to-fructose ratio. More recent work has pushed this closer to 1:0.8, and some World Tour teams now use ratios near 1:1.
The practical result: a trained gut using a dual-source mix can absorb 90-120g of carbohydrate per hour, double the glucose-only ceiling. World Tour teams have pushed even higher — Dan Lorang, Head of Performance at Red Bull-Bora-Hansgrohe (who coaches Frodeno, Haug, and Cavendish), has reported 100-130g per hour in grand tour stages. Those figures require months of systematic gut training and bespoke product formulation. The realistic ceiling for most amateur cyclists is 80-100g per hour, which still represents a 100-150% increase over what most amateurs currently eat.
Over a five-hour event, the difference between 40g/hr and 90g/hr is 250 grams of additional carbohydrate — roughly 1,000 extra calories delivered to working muscles.
What this means for your race plan
Every product you consume during a race should contain both glucose and fructose sources. Check labels for maltodextrin or dextrose (glucose sources) paired with fructose. If your gel or drink mix lists only maltodextrin, you are capped at 60g per hour no matter how many you eat. Most modern sports nutrition brands have caught up with this research, but check anyway.
You can model your daily calorie needs and in-ride carbohydrate targets using the Fuel Planner, which calculates macro splits and in-ride carbs based on your weight, ride duration, and session intensity — built on the fuel-for-the-work-required framework that Sam Impey's research formalised.
Gut Training: The Four-to-Six-Week Protocol
Your gut is a trainable organ. The density of SGLT1 and GLUT5 transporters in the intestinal wall increases with repeated exposure to carbohydrate during exercise. Cox et al. (2010) showed measurable improvements in exogenous carbohydrate oxidation after just 28 days of consistent gut training. But you cannot skip this step. Attempting 90g per hour on race day without gut training is a recipe for GI disaster.
For the full protocol breakdown, read the dedicated gut training guide for endurance cyclists. Here is the condensed version.
Week-by-week progression
Weeks 1-2: Establish your current comfortable intake. For most untrained guts, this is 30-40g per hour. Use a dual-source product (glucose + fructose) from the start.
Weeks 3-4: Increase to 50-60g per hour on your longer training rides (two hours or more). Practise at moderate intensity — not just easy zone 2, because blood flow diverts away from the gut as intensity rises.
Weeks 5-6: Push to 70-80g per hour. This is where most riders hit their first discomfort. If GI issues appear, hold at the current level for another week before progressing.
Weeks 7-8: Reach your race target of 80-100g per hour. Some riders will push beyond this. Others will find 80g is their ceiling, and that is fine — 80g per hour is still double what most amateurs eat.
Rules that make gut training work
Use the products you plan to race with. Gel tolerance is product-specific, not universal. A gel that works in training will work in racing; one you have never tried is a coin flip.
Train your gut at race-similar intensities. Zone 2 rides are gentler on the stomach than threshold efforts. If you only practise fuelling at low intensity, expect trouble when the pace lifts.
Stay hydrated. Dehydration slows gastric emptying and worsens every GI symptom. The Hydration Calculator can help you set a baseline fluid target for your body weight and conditions.
Avoid high-fibre and high-fat foods within three hours of riding. Fibre slows gastric emptying. Fat slows it further. Both are fine for general health but counterproductive when you need rapid carbohydrate delivery.
Timing Windows: Pre-Race, First Hour, Deep Into the Ride
48 hours before: carb loading done right
The old-fashioned depletion-then-load protocol is dead. Modern carb loading is simpler: 8-12g of carbohydrate per kg bodyweight per day across the 48 hours before an event. For a 75kg rider, that is 600-900g of carbs per day — a significant amount that requires deliberate effort.
This is where most riders fail. They eat a big pasta dinner the night before and assume they are loaded. They are not. A single meal cannot fill 400-500g of glycogen storage. It takes sustained high-carb eating across two full days: rice, bread, pasta, potatoes, fruit, juice, sports drink — stacked across breakfast, lunch, dinner, and snacks.
Keep protein moderate (1.6-2g/kg), keep fat low (to leave room for carbs), and keep fibre low (to avoid bloating). For a thorough timeline, see the race day fuelling 24-hour timeline.
Race morning: 3-4 hours before the start
Eat 1-3g of carbohydrate per kg bodyweight at breakfast, three to four hours before the start. For a 75kg rider, that is 75-225g — the equivalent of a large bowl of porridge with honey and banana, plus toast and jam, plus a glass of juice.
This meal tops off liver glycogen that was depleted overnight. Skip it and you start the race with a 20-30% deficit in liver stores, which matters because the liver is the primary source of blood glucose for the brain. Bonking is partly a central nervous system event — your brain runs out of fuel before your legs do.
The first 20 minutes
Start eating immediately. Not at 30 minutes. Not when you feel hungry. Within the first 20 minutes of any event over 90 minutes. Front-loading fuel is the single most effective tactical change in race nutrition. The carbohydrate you consume in hour one is absorbed and available for hour three. The carbohydrate you skip in hour one is gone forever — there is no catching up.
A practical approach: have a gel or a few swigs of concentrated drink mix within the first 15 minutes, then set a timer on your head unit for every 20 minutes as a feed reminder.
Hours 1-3: the accumulation phase
This is where discipline matters. You feel strong. Your legs are good. Eating feels unnecessary. Eat anyway. Target your planned carb intake — 60-90g per hour for most events — and spread it evenly across the hour rather than consuming everything in one bolus.
Rotate between sources to reduce gut fatigue: drink mix as a steady drip, gels for concentrated top-ups, solid food (rice cakes, dates, banana) for variety. The guide to in-ride nutrition covers product rotation in detail.
Hours 4+: the payoff
If you fuelled correctly in hours one through three, hours four and beyond are where you overtake the riders who did not. This is the zone where the bonk claims victims — the riders who ate 30g per hour and are now 150-200g behind on total carbohydrate.
Maintain your intake. If anything, this is the time to increase slightly — push toward the higher end of your trained range. If your stomach starts to rebel, dial back to liquid calories only (drink mix) and avoid solid food. Concentrated drink mix is your emergency fuel format: easy to consume, fast to absorb, no chewing required when your jaw is tired.
If you want to check whether your overall daily calorie burn supports your fuelling plan, the Calories Burned Calculator gives a ride-specific estimate.
What to Eat at What Intensity
Fuelling is not one-size-fits-all across intensity zones. The fuel mix your muscles burn changes with effort level.
Zone 2 (endurance, 55-75% FTP)
At low intensity, fat oxidation contributes significantly to energy production. Carbohydrate needs are lower — 30-60g per hour is usually sufficient for rides under three hours. Longer zone 2 rides (four hours and beyond) should increase to 60-80g per hour because total glycogen depletion still occurs, just more slowly.
This is also where fuel-for-the-work-required periodisation applies. Low-intensity training rides can be done with lower carb intake to support fat oxidation adaptations. Race day, however, always gets full fuel.
Tempo and sweetspot (76-90% FTP)
Carbohydrate becomes the dominant fuel source. Target 60-80g per hour. Most sportives involve long tempo efforts — sustained group riding, rolling terrain, the push to stay with the bunch. These efforts burn through glycogen faster than pure zone 2, and under-fuelling here is the most common sportive mistake.
Threshold and above (90%+ FTP)
At high intensity, carbohydrate is almost the sole fuel source, and blood flow is diverted away from the gut toward working muscles. Absorption capacity drops. This is why liquid calories (drink mix) become increasingly important as intensity rises — they require less digestive effort than solid food.
Target 80-100g per hour if you have trained your gut for it. If your event includes high-intensity surges (crits, road races with attacks), front-load solid food during easier phases and switch to gels and drink mix when the pace rises.
Sodium and Fluid Balance During Racing
Most amateur fuelling guides focus exclusively on carbohydrate and ignore sodium. That is a mistake. Sodium is the primary electrolyte lost in sweat, and the consequences of sodium depletion — cramping, cognitive decline, nausea, progressive dehydration — mimic many of the symptoms riders attribute to bonking.
How much sodium you lose
Sweat rates vary from 500ml to over 2 litres per hour depending on heat, humidity, fitness, and genetics. Sodium concentration in sweat ranges from 200mg to over 1,500mg per litre. A moderate sweater in warm conditions might lose 700-1,000mg of sodium per hour. Over a five-hour gran fondo, that is 3,500-5,000mg of sodium — a massive deficit if all you drink is water.
Practical sodium strategy
Add 500-700mg of sodium per hour as a starting point. Electrolyte tablets in your bottles are the simplest approach. Some drink mixes already contain adequate sodium (check the label — many do not). In hot conditions or for heavy sweaters, increase to 1,000mg per hour.
Signs of sodium depletion during a ride: muscle twitching or cramping, salt crust on your kit, headache, unusual fatigue despite adequate carbohydrate intake. If you recognise these, increase sodium immediately — an electrolyte capsule or salt tablet takes effect within 15-20 minutes.
Fluid targets
Drink 500-750ml per hour as a baseline. In cool conditions, 500ml is enough. In hot conditions, push to 750ml or beyond. Weigh yourself before and after a training ride to calibrate — every kilogram lost is roughly one litre of fluid deficit.
Do not overdrink. Hyponatraemia (dangerously low blood sodium from excessive water intake) is rare but serious. Drink to thirst as a guide, with your electrolyte strategy handling the sodium side. The Hydration Calculator gives a personalised fluid and sodium target based on your body weight and riding conditions.
Training Fuel vs Race Fuel
The fuelling strategy for a Tuesday interval session is not the same as the strategy for Saturday's race.
Training fuel is periodised. Carbohydrate intake should match the session demands — this is the fuel-for-the-work-required principle. A zone 2 ride might use 30-40g per hour. A hard interval session gets full fuelling. A rest day needs minimal carbohydrate. This periodisation preserves metabolic flexibility and prevents chronic over-fuelling. The Energy Availability Calculator can help you check whether your total daily intake supports both training and recovery.
Race fuel is maximal. On race day, periodisation goes out the window. The goal is maximum carbohydrate delivery from the moment the race starts. No fat oxidation priority, no strategic under-fuelling, no train-low logic. If your training rides use 40-60g per hour, jumping to 80-100g per hour on race day is a significant increase — which is precisely why gut training matters. Your gut needs to have rehearsed race-level intake before race day arrives.
Expect the scale to jump. In training, you might run a modest calorie deficit to nudge body composition. In the 48 hours before a race, you eat in a deliberate surplus to maximise glycogen storage. Every gram of glycogen stored binds 2.7g of water, so expect to gain 1-2kg the day before a race. This is fuel, not fat. The Race Weight Calculator can help you set a target that accounts for these fluctuations, and the Body Composition Calculator gives context for where you sit relative to performance benchmarks.
Worked Example: Four-Hour Sportive
Rider profile: 75kg, FTP 250W, riding at 65-75% FTP for four hours.
48 hours before
Carb loading at 8-10g/kg per day = 600-750g carbs per day. This means rice or pasta at every meal, fruit and juice between meals, sports drink sipped throughout the day. Protein at 1.8g/kg (135g/day). Fat reduced to make room for carbs.
Race morning (4 hours before start)
Breakfast: 2g/kg carbs = 150g. A large bowl of porridge (80g oats) with honey and banana, two slices of white toast with jam, glass of juice. Coffee as usual.
Sip 500ml of water with an electrolyte tab between breakfast and the start. A gel or small snack 15 minutes before the start if more than four hours have elapsed since breakfast.
On the bike
Target: 70-80g carbohydrate per hour, 500-700ml fluid per hour, 500-700mg sodium per hour.
Hour 1: Two bottles mixed with 40g carb drink mix each (80g total across two bottles over the ride). One gel at 15 minutes (25g carbs). One gel at 40 minutes (25g carbs). Total: ~50g from gels + steady drip from bottles.
Hour 2: One gel at 1:00 (25g). Half a rice cake at 1:20. One gel at 1:40 (25g). Continue drinking.
Hour 3: One gel at 2:00 (25g). One gel at 2:30 (25g). Banana piece at 2:45. Continue drinking. Check sodium — if cramping or twitching, add an electrolyte capsule.
Hour 4: Switch to liquid only if stomach is tired. One gel at 3:00 (25g). Sip drink mix steadily. One gel at 3:30 (25g). Push to the finish.
Total intake: ~280-320g carbohydrate, 2-2.5L fluid, 2,000-2,800mg sodium.
Worked Example: Six-Hour Gran Fondo
Rider profile: 80kg, FTP 230W, riding at 60-70% FTP with two significant climbs.
48 hours before
Carb loading at 10g/kg per day = 800g carbs per day. Aggressive loading — every meal is carb-dominant, snacking on dried fruit, rice cakes, and energy bars between meals.
Race morning (3.5 hours before start)
Breakfast: 2.5g/kg carbs = 200g. Large porridge, toast, banana, juice, energy bar. Top up with a bottle of carb drink mix in the 90 minutes before the start.
On the bike
Target: 80-90g carbohydrate per hour, 600-750ml fluid per hour, 700-1,000mg sodium per hour.
Hours 1-2 (flat/rolling, group riding): Two gels per hour (50g) plus drink mix (30-40g per bottle). Solid food — rice cakes, date bars — every 30 minutes for variety. The early hours are when you can eat solid food comfortably. Front-load it.
Hours 3-4 (first major climb and descent): Eat on the approach to climbs, not during them. On a hard climb, blood diverts from the gut and absorption drops. Take a gel 10 minutes before each significant ascent. On descents, eat solid food while the pace is lower. Maintain 80g per hour through a mix of gels and drink.
Hours 5-6 (second climb and finish): By now, gut fatigue may be setting in. Shift toward liquid calories — drink mix and gels only. Maintain 70-80g per hour minimum. If you feel strong, push to 90g. If your stomach rebels, drop solid food entirely and rely on sipping concentrated drink mix.
Total intake: ~480-540g carbohydrate, 3.5-4.5L fluid, 4,200-6,000mg sodium.
The difference between this rider and the one who bonks at hour four is roughly 200g of carbohydrate consumed across the first three hours. That is four extra gels, or two bottles of properly mixed drink. A small logistical effort for a transformative performance outcome.
Real Food vs Gels vs Drink Mix
The body does not care whether its glucose arrives via a gel, a rice cake, or a banana. What matters is total carbohydrate per hour, the glucose-to-fructose ratio, and whether the product sits well in your gut.
Gels are fast, portable, and precisely dosed (20-30g carbs each), but flavour fatigue sets in after six or eight of them. Drink mix is the most underrated tool — a properly concentrated bottle (60-80g carbs per 750ml) delivers carbohydrate, fluid, and electrolytes simultaneously with zero chewing. At high intensity, drink mix is often the only format you can tolerate. Real food — rice cakes, date bars, banana pieces, jam sandwiches on white bread — works well in the first half of long events when the gut is fresh and intensity is manageable. For recipes, the guide to homemade race fuel covers the basics.
The best race plans use all three: drink mix as the steady baseline, gels for precise top-ups, and real food in the early hours for variety. This rotation prevents gut fatigue from any single product.
Building Your Personal Race Day Plan
Every rider's plan will differ based on body weight, event duration, intensity, heat conditions, and gut tolerance. Here is a six-step framework.
Step 1: Establish your baseline. What can you currently eat per hour without GI distress? That is your starting point, not your target.
Step 2: Set your race target. Events under two hours: 60g/hr. Two to four hours: 60-80g/hr. Four hours and beyond: 80-100g/hr. Use the Fuel Planner to calculate personalised targets based on your weight and ride profile.
Step 3: Train your gut. Four to six weeks minimum. Increase by 10g per hour every one to two weeks. Use your race products. Practise at race-like intensities.
Step 4: Plan your product mix. Calculate how many gels, how much drink mix, and how much solid food you need per hour. Multiply by ride duration. Add 20% contingency.
Step 5: Rehearse the full plan. At least two long training rides at race-level intake before the event. If something causes problems, find out in training — not at kilometre 120.
Step 6: Execute without thinking. On race day, follow the plan mechanically. Set feed reminders. Eat before you are hungry. Drink before you are thirsty. The plan removes decision-making when your brain is fatigued and your instincts are unreliable.
Common Race Day Fuelling Mistakes
Waiting until hungry to eat. Hunger is a trailing indicator of glycogen depletion. By the time you feel hungry on the bike, you are 30-45 minutes behind on fuel.
Trying new products on race day. Every gel, bar, and drink mix should be tested in training first. The feed zone at kilometre 80 is not the place to discover that a brand triggers nausea.
Drinking water instead of carb drink. Water replaces fluid but delivers zero carbohydrate. Fill both bottles with drink mix. Carry water separately if you need it for pouring over your head.
Ignoring sodium in the heat. Sodium losses accelerate in warm conditions while most riders just drink more water — diluting their remaining sodium further. This is entirely preventable with proper electrolyte intake.
Under-loading in the 48 hours before. If you arrive at the start line with half-filled glycogen stores because you were "eating clean" the day before, no amount of on-bike fuelling can compensate. If you want to check that your daily intake supports your training load, run your numbers through the Energy Availability Calculator.
The Bottom Line
Race day fuelling is not complicated. It is precise. The research is settled: 60-90g of carbohydrate per hour for most events, rising to 90-120g for long-course racing, delivered via a glucose-fructose mix, supported by adequate sodium and fluid, and rehearsed through weeks of progressive gut training.
The riders who execute this consistently — who eat early, eat enough, and eat what they have practised — finish stronger than riders with better power numbers who underfuelled. I have seen it hundreds of times. A well-fuelled 3.5 w/kg rider will ride away from a glycogen-depleted 4.0 w/kg rider in the final third of any event over three hours.
Build your plan. Train your gut. Run your numbers through the Fuel Planner. Then eat the food, drink the drink, and finish the race with something left in the tank. That is the whole strategy.