What Do Energy Gels Do for Endurance?
The gel you skip at 90 minutes is the one you think about at kilometre 35. Pace that felt controlled starts to cost more. Your stride shortens. Concentration slips. The legs are still moving, but the engine behind them is running low — and you feel a missed feed long before a watch shows it.
That's the honest answer to what energy gels do. They deliver fast, usable carbohydrate during exercise, so you can hold pace, power and judgement when your own stores start to run down. They don't make you fitter. They protect the fitness you already have from falling apart in the second half of a long effort.
Used well, a gel is the difference between a strong final 10km and a survival shuffle. Used badly — too little, too late, never rehearsed — it does almost nothing, and the athlete walks away convinced gels "don't work."
"People think of a gel as a snack. It isn't. It's a carbohydrate delivery system, and the only questions that matter are how much it delivers, how fast your gut can absorb it, and whether you can take it again an hour later. We built the truefuels gel around 40g and a 1:1 ratio because that's what lets you hit a real hourly target without carrying five wrappers and a stomach ache."
— Alistair Brownlee, Two-time Olympic Triathlon Champion and founder of truefuels
What energy gels actually do in the body
During hard or long exercise, your body leans heavily on carbohydrate — the glycogen stored in muscle and liver, plus glucose in the blood. Those stores are finite. When they fall too far, power output drops, perceived effort climbs, and the bonk arrives.
A gel tops up carbohydrate availability before that decline becomes costly. Once consumed, the carbohydrate is absorbed into the bloodstream, where it's either used immediately or spares your remaining glycogen. There's also a faster effect: carbohydrate detected in the mouth has a central signal that makes effort feel more manageable even before full absorption. Over a long session, the metabolic effect is the bigger one, but both matter.
The key point is that a gel supplements a system rather than creating energy from nowhere. Start poorly fuelled, take it too late, or take too little across a long event, and the benefit shrinks. Gels work as part of a plan, not as an emergency fix.
Why carbohydrate becomes the limiter
Short, easy sessions rarely need mid-workout fuelling. A steady 40-minute jog is one thing. A two-hour run with marathon-pace work, a long ride with threshold blocks, or a half Ironman bike leg is another.
As duration and intensity rise, carbohydrate demand rises with them. Fat contributes energy, but it can't sustain higher race intensities on its own. Hold a meaningful pace for long enough and carbohydrate availability becomes the ceiling. That's where gels earn their place — they let you carry a precise amount of carbohydrate in a small package, take it quickly, and keep moving.
Carbohydrate targets by session
Most athletes should think in grams of carbohydrate per hour, not number of gels. That's the metric that decides whether you're actually fuelled.
| Session / event | Duration | Carb target (g/hr) | Gel approach |
|---|---|---|---|
| Easy aerobic run or ride | <60–75 min | 0–20g | Pre-session meal usually enough |
| Steady long run or ride | 75 min–2hr | 30–60g | 1 gel every 30–40 min from start |
| Marathon-pace long run | 2–3hr | 60–80g | 1 gel every 20–25 min |
| Marathon race | 3–5hr | 60–90g | 2–3 gels per hour, start at 20–30 min |
| Long ride / sportive | 2.5–5hr | 60–90g | Gels + drink; start within 20 min |
| Half / full Ironman | 4–14hr | 60–90g | Consistency over ambition |
These are working targets to test in training, not prescriptions. Build towards the higher numbers — the gut adapts to higher intake the same way the legs adapt to mileage.
Why some gels deliver more than others
Not all gels are built the same, and the difference is measurable. The biggest variable is the carbohydrate source and ratio. Many gels use glucose alone, which is absorbed through a single intestinal transporter — SGLT1 — that saturates at roughly 60g per hour. Take more than that from glucose alone and the excess sits in the gut.
A 1:1 glucose-to-fructose ratio solves this. Fructose is absorbed through a separate transporter, GLUT5, so both pathways run at once and absorption can climb to 90–120g per hour without overwhelming a single route. The truefuels Performance Gel is built on that 1:1 ratio at 40g per gel. Most standard gels carry 20–30g, which means you'd need 4–5 per hour to approach the same intake — more to carry, more to open, more flavour fatigue over three or four hours. With 40g per gel, 2–3 covers most race targets.
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 →Fuel and fluid are one system
A gel rarely fails on its own. Carbohydrate, fluid and sodium have to work together. Energy gels are concentrated by design, and taking one without enough fluid raises the chance of stomach discomfort, especially at high intensity or in heat.
Sodium isn't a side note here. In the gut, sodium co-transports glucose through SGLT1, so it actively improves carbohydrate absorption — which is why the truefuels gel carries built-in electrolytes rather than leaving them out. In hot conditions or for heavy sweaters, adding a truefuels Active Hydration sachet covers the extra sodium demand without overloading the carbohydrate concentration in your bottle.
When to take a gel
For most athletes, gels become useful once a session passes 60–90 minutes, especially at moderate-to-high intensity. In racing they often make sense earlier, because the cost of getting behind on fuelling is high and catching up mid-race is difficult.
The common mistake is waiting until you feel empty. By then performance has already slipped. Carbohydrate takes 15–20 minutes to reach the bloodstream, so fuel proactively — on a schedule, not on appetite. A runner targeting a first marathon or a triathlete on the bike should think in terms of "every 20–30 minutes," and let that schedule lead the decision.
Common mistakes athletes make
Taking too little. Two gels feels like fuelling, but the actual carbohydrate may be well below what the session demands. Count grams per hour, not wrappers.
Fuelling late. A large dose deep in the race rarely sits as well as steady intake from early on. The gut handles consistency far better than panic.
Never practising. Race day is the wrong place to discover a flavour turns your stomach or your target is too ambitious. Fuelling is trainable — treat it that way.
Isolating the gel from the system. Low sodium, poor hydration or a thin pre-race breakfast will make a perfectly good gel feel like the problem.
So, what do energy gels do when used properly?
They protect performance. They supply a controlled stream of carbohydrate when your body needs it most, reduce the risk of a sharp energy drop, and make it easier to execute your pacing and fuelling plan under pressure.
More isn't automatically better. The right intake is the one you can absorb, tolerate and repeat — and that number changes with conditions, intensity and gut training. The athletes who fuel well aren't guessing. They know their hourly carbohydrate target, match it to the session, and have rehearsed it until it's automatic. When fuelling stops being improvised, performance becomes far more predictable.
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 →Know your hourly carb target — then make it automatic.
The Fuelling Protocol tool calculates your carbohydrate and sodium targets from your weight, pace and distance, so fuelling stops being guesswork.
