TL;DR
Take your first GU gel at 45 minutes, then one every 45 minutes after that. Don't wait until you feel flat — by then you're already behind. Fuel before you need it, drink water with every gel, and save caffeine gels for the back half when things get dark.
You've got your favourite selection of GU Energy gels. You know what they do. You know why they work. Now comes the part where most people still get it wrong.
They wait. And wait. And then, at kilometre 28, when their legs have already started sending resignation letters, they eat three gels in a row and wonder why they feel sick.
Don't be that person. Here's how to actually time it.
Start before you need it
This is the one rule that matters more than any other: fuel before you feel flat, not after.
By the time you notice your energy dropping, your glycogen stores are already critically low. The gel you take then needs 10–15 minutes to kick in, which means you're running on fumes for the best part of 20 minutes. In a race, that's an eternity.
Fuelling is not a rescue plan. It's a maintenance schedule.
The 45-minute rule
Simple, repeatable, works for almost everyone: take your first gel around the 45-minute mark, then one every 45 minutes after that. Sip water every 15–20 minutes throughout.
For a 3-hour long run, that looks like this:
• 45 min: first gel
• 1:30: second gel
• 2:15: third gel
• Finish: eat something real and sit down
Three(ish) energy gels over three(ish) hours. Consistent energy. No wall. No drama.
Adjust for how hard you're working
The 45-minute rule is a baseline. Intensity changes things:
• Easy run under 60 min: skip the gel, you'll survive
• Moderate effort over 60 min: one gel around the 45-minute mark (but that depends on how you’re feeling – might not need it.
• Hard effort or race pace: start slightly earlier (30 min) and stick to every 45 min
• Ultra distance: aim for 60–90g of carbs per hour: that's 2–3 gels, plus whatever else you're using
Caffeine energy gels: save them for when you need the edge
Caffeinated GU Energy flavours are most useful in the back half of a long effort - when your legs are tired and your brain is trying to negotiate an early finish. Using them too early wastes the effect. Save them for the final hour, or a section you know is going to be rough.
A note on gut issues
If energy gels have ever made you feel sick mid-run, the most likely culprit is one of three things: you took it without water, you took it too late (already dehydrated), or your gut just hasn't practised enough.
The cure is boring but true: use gels in training, regularly, at race effort. Your gut is trainable. Give it a chance to catch up.
The messiest runs teach you the most. Spill a gel, bonk once, forget to drink - then never do it again.
Build the habit in training. Trust it on race day. Fuel first, every time.
That's the GU Energy gel series done. Next, we go deeper: hydration, recovery, race-specific plans, and the art of eating real food while moving fast through the mountains.
Frequently Asked Questions
When should I take my first gel? ▼
Around the 45-minute mark, before you feel any energy drop. By the time you notice you're flagging, your glycogen is already critically low and a gel takes 10–15 minutes to kick in. Front-foot fuelling beats reactive fuelling every time.
How many gels do I need for a long run? ▼
One every 45 minutes from the 45-minute mark. For a 3-hour run that's roughly three gels. For ultras, you're targeting 60–90g of carbs per hour - that's 2–3 gels per hour combined with whatever else you're carrying. The longer the effort, the more the maths matters.
When should I use a caffeinated GU gel? ▼
Save caffeine gels for the back half of your run - the final hour, or any section you know is going to be rough. Using them too early burns through the effect when you don't need it most. Think of them as a tool for the hard part, not the warm-up.
Why do gels make me feel sick? ▼
Usually one of three things: you took it without water, you took it too late when you were already dehydrated, or your gut hasn't had enough practice at race effort. The fix is boring but it works - use gels regularly in training at the same intensity you race. Your gut adapts, it just needs the reps.
Do I need a gel for a run under an hour? ▼
Not usually. An easy run under 60 minutes at moderate effort is well within what your glycogen stores can handle without top-up. Save the gels for sessions over an hour, hard efforts, or back-to-back training days where your stores are already depleted going in.
Why Energy Gels, Like GU, Work (Your Body Is Smarter Than You Think)?
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