Endurance Fueling Guide for Race Performance
You don't lose a race at kilometre 35. You lose it at kilometre 5, when you decided the gels could wait a little longer. Or the night before, when you skipped the sodium with dinner because you were already focused on sleep. Or three weeks ago, when you stopped testing your nutrition in long sessions because you were confident it would hold.
Race day exposes preparation, not fitness. The two athletes who trained identically often perform very differently — and when the gap can't be explained by pacing errors or conditions, it almost always comes down to fuel. One had a plan. One was improvising.
This guide is about having the plan.
"I've always treated nutrition the same way I treat intervals — with specific targets, tested under pressure, and adjusted when the data says to adjust. The athletes I see struggling late in races are almost never under-trained. They're under-fuelled. They waited too long to start, took too little, or tried something on race day that they'd never rehearsed. The protocol protects your fitness. Without it, you're just hoping the training shows up."
— Alistair Brownlee, Two-time Olympic Triathlon Champion and founder of truefuels
What a useful endurance fueling guide actually gives you
Numbers. Not vague advice. For most runners, cyclists and triathletes, three variables determine whether nutrition supports or limits performance: carbohydrate per hour, fluid per hour and sodium per hour. Get those broadly right and you protect against bonking, dehydration, electrolyte-related fade and the late-race decision-making deterioration that often precedes the legs giving out.
Carbohydrate is the priority. Stored glycogen is finite. Once session duration moves beyond 75–90 minutes — or intensity demands rapid energy turnover — taking in carbohydrate during exercise stops being optional. The target for most trained endurance athletes sits between 60 and 90g per hour, rising to 90–120g per hour for experienced athletes who have trained their gut for high intake rates.
Fluid is more individual than most advice acknowledges. Sweat rate varies enormously between athletes and conditions. A cool spring half marathon and a hot middle-distance triathlon are not the same physiological problem. Drinking to a fixed schedule without accounting for your own sweat rate leads to underfuelling in heat and overfuelling in cool conditions. Both cost performance.
Sodium is the variable most athletes still underweight. When sweat losses are high, replacing fluid without enough sodium leaves you flat, nauseous and increasingly difficult to rehydrate. The truefuels Active Hydration sachet delivers 390mg sodium per 500ml — calibrated to the average sweat-matched range established by GSSI and NIH research — rather than the 1,000–1,500mg found in products designed for extreme conditions.
Fuelling targets by event type
Not every session needs the same plan. Duration, intensity and conditions determine the starting point.
| Event / session type | Duration | Carb target (g/hr) | Fluid target (ml/hr) | Sodium target (mg/hr) | Key principle |
|---|---|---|---|---|---|
| Easy aerobic run or ride | <75 min | 0–20g | 300–500ml | Low | Pre-session meal covers most needs |
| Steady long run | 90 min–2hr | 40–60g | 400–600ml | 300–500mg | Start gels at 20–30 min |
| Marathon race | 3–5hr | 60–80g | 400–700ml | 400–700mg | Consistent every 20–25 min |
| Hard long ride / sportive | 2.5–5hr | 60–90g | 500–750ml | 500–800mg | Bike is the feeding window |
| Half Ironman (70.3) | 4–6hr | 60–90g | 500–800ml | 500–1,000mg | Bike fuels the run |
| Full Ironman | 8–14hr | 60–90g | 500–800ml | 600–1,000mg | Consistency over ambition |
| Hot race (any) | Any | Upper range | Upper range | Upper range | Pre-load sodium before start |
| Threshold / interval session | <90 min | 30–45g | 400–600ml | 300–500mg | One gel at start if key session |
At 40g per truefuels gel and a 1:1 glucose-to-fructose ratio, hitting 80g/hr means 2 gels per hour — activating both the SGLT1 and GLUT5 intestinal transporters simultaneously. This is the mechanism behind the 90–120g/hr ceiling that research on elite athletes has established: two separate absorption pathways running in parallel rather than one being overwhelmed.
Before the race: where most plans actually fail
Pre-race nutrition is not breakfast. It is the 24–48 hours that precede breakfast.
If glycogen is not topped up through consistent carbohydrate intake across the two days before a race, breakfast cannot compensate. Eat familiar carbohydrate-rich meals, reduce fibre and fat, drink consistently and include sodium — particularly if travelling, racing in warm conditions, or someone who wakes slightly under-hydrated.
Race morning: carbohydrate-led meal 2–4 hours before the start. Low fibre, low fat, familiar. Porridge, white toast, rice, banana, bagel. The specific food matters less than the reliability. If it hasn't worked on a long training morning, it hasn't earned its place on race morning.
In the 15–20 minutes before the start, a small carbohydrate top-up maintains blood glucose as intensity rises. One truefuels gel — 40g in a fluid, easily absorbed format — is the cleanest option. No fibre, no fat risk, nothing your gut hasn't already processed.
If conditions are warm, include sodium in your pre-race fluids. Sodium improves fluid retention before the race demands begin. This is the same logic behind truefuels' inclusion of sodium in the Performance Gel itself — sodium co-transports glucose through the SGLT1 transporter, actively improving carbohydrate absorption rather than just replacing sweat losses.
truefuels Performance Gel
40g of carbohydrate at a 1:1 glucose-fructose ratio, with electrolytes built in. Two salt variants, water-mixable, and free from artificial flavours, sweeteners and preservatives — so you can take 2–3 an hour without the gut cost.
See the gel →During the race: the numbers in practice
Carbohydrate
Start within the first 20–30 minutes — before you feel like you need it. Carbohydrate takes 15–20 minutes to enter the bloodstream. You are fuelling for 30 minutes from now, not for right now.
Even spacing works better than reactive bursts. One gel every 20–25 minutes is easier on the gut and steadier in delivery than two gels at once when energy drops. For athletes pushing towards 90g/hr, the combination of the 40/1.0 gel (386mg sodium, 40g carbohydrate) and a structured drinking pattern covers both the fuel and the electrolyte target simultaneously.
Fluid
400–800ml per hour as a starting point. Adjust for body size, conditions and sweat rate. Lighter athletes in cool conditions may sit at the lower end; larger athletes or heavy sweaters in heat will need more. The target is limiting excessive dehydration without the stomach becoming the problem.
Sodium
300–800mg per hour in moderate conditions, rising to 800–1,000mg+ in heat or for heavy sweaters. The truefuels gel system delivers sodium inside each gel — 98mg (40/0.25 variant) or 386mg (40/1.0 variant). For most sessions, the gel variants cover sodium needs. In hot races or for heavy sweaters, adding an Active Hydration sachet per 500ml provides the additional layer.
Why athletes get GI distress — and how to prevent it
Most stomach problems during endurance events are predictable. They come from taking too much too late, using a concentration that's too strong without enough fluid, or using products on race day that were never tested at race intensity.
If you struggle with gels, the problem is often not the gel itself. It's the timing. Taking two gels in ten minutes after an hour of under-fuelling, then chasing them with too little water — that's a protocol failure, not a formulation failure. Similarly, athletes blame sodium when the real issue is total carbohydrate concentration in the gut without adequate fluid to move it through.
The truefuels gel's fluid texture and unflavoured, additive-free formulation are designed to reduce the most common causes of GI distress: high osmotic load from sweeteners, thick texture that slows gastric emptying, and flavour fatigue that makes athletes stop drinking when they most need to. It was tested by over 50 co-creators specifically at real race conditions before release.
Train the gut like any other system. Start with a carbohydrate intake you tolerate, then build over several long sessions. Practise at race pace, not just easy days. Running is less forgiving than cycling because of the mechanical load on the stomach — marathon fuelling demands more care than the equivalent hourly intake on the bike.
Event-specific adjustments
Marathon: Early commitment is non-negotiable. If you wait until 18km to start fuelling properly, you're already chasing a deficit that's very difficult to close. First gel within 25 minutes of the start. Every 20–25 minutes thereafter. Consistent and automatic.
Half Ironman: The bike is the nutritional foundation of the race. Easier to fuel than the run, more stable conditions, and the window where most of the carbohydrate target should be hit. Athletes who dismount underfuelled typically spend the run surviving rather than racing.
Long cycling: The best environment to build gut tolerance. Lower mechanical stress, easier to eat and drink, slower pace absorption changes. Use long rides to progressively increase hourly carbohydrate intake across training blocks. By race day, 80–90g/hr should feel unremarkable.
Build a protocol, not a shopping list
The strongest fuelling plans are boring in the best sense. Repeatable. Measured. Easy to execute when heart rate is elevated and decision-making capacity is reduced.
Before every key session and race, answer these four questions:
1. What am I eating in the final hour before the start?
2. How many grams of carbohydrate per hour during the event?
3. How much fluid — and at what sodium concentration?
4. What changes if conditions turn warm?
If you can't answer those clearly, the plan isn't ready.
The truefuels system — Performance Gels in both salt variants, Active Hydration sachets and CoreCtrl for heat — is built around the principle that exact delivery beats improvisation every time. Not because using more products improves performance, but because a system with precise carbohydrate and sodium delivery reduces the decisions you have to make when you most need to be focused on the race.
Your ideal plan is personal. Some athletes perform best at 90g carbohydrate per hour. Others race better at 70g with higher fluid. Some need aggressive sodium support in heat. Others don't. The goal is not to copy another athlete's numbers — it's to test, refine and arrive at a protocol you trust completely.
Race fitness gives you the ceiling. Fuelling determines how close you get to it.
40g of carbohydrate. 1:1 ratio. Nothing else.
The truefuels Performance Gel delivers 40g of carbohydrate per serving in a 1:1 glucose-fructose ratio, with electrolytes built in. Two salt variants. Water-mixable. Informed Sport certified.
See the gel →Turn this guide into your plan.
The Fuelling Protocol tool converts your race distance, pace and conditions into exact carbohydrate and sodium targets.
