Half the runners who buy energy gels have no physiological need for them on the day they swallow them. They take one at kilometre five of a 10K because the person next to them did, and the only thing it changes is the taste in their mouth.
The useful question is not which brand to buy. It is how many running energy gels your race actually demands, and when to take them so the carbohydrate arrives before you need it rather than after. This guide covers the dose by distance, the timing, why dual-source carbohydrate raises the ceiling, what to check on a label, and a homemade version that costs almost nothing.
- How many gels per distance
- Why dual-source carbohydrate changes the ceiling
- When to take them, before and during
- What to check on the label
- The homemade gel
- Running energy gels FAQ
How many gels per distance
Before you choose a product you need to know the quantity of carbohydrate per hour your effort requires. That number picks the gel for you, not the other way round.
| Distance | Time on feet | Carbohydrate intake | In gels |
|---|---|---|---|
| 5K and 10K | Under 75 minutes | None, your stores cover it | Zero |
| Half marathon | 75 to 150 minutes | 30 to 60 g per hour | 1 to 2 per hour |
| Marathon | Over 2 h 30 | 60 to 90 g per hour | 2 to 3 per hour, dual-source |
| Long trail and ultra | Over 5 hours | 90 to 120 g per hour if adapted | 3 to 4 per hour plus solid food |
Short runs of 30 to 60 minutes
No gel at all. Your glycogen stores comfortably cover the effort, and a banana does the same job for a fraction of the price. If you are still building the habit of running regularly, the money is far better spent on shoes than on sachets. Our 8-week 5K programme gets you there without any of it.
10K and half marathon
One gel around halfway is enough, and a good part of its effect is mental. There is no reason to buy a premium product for this duration. Any basic gel does the work, which is worth knowing before you spend three times as much. The 8-week 10K plan is a sensible place to rehearse the timing.
Marathon and beyond
Three to five gels, planned in advance, not taken on instinct when you start feeling flat. On trail and ultra, mix gels with solid food: the stomach turns against sweet flavours after a few hours, and the runner who planned only gels is the one walking at hour six.
One warning that matters more than any brand choice. These ranges assume a trained gut. Taking 90 g per hour on race day without ever having practised it is the most reliable way to end your race in a portable toilet at kilometre 30. Nutrition is trained, exactly like your intervals.
Why dual-source carbohydrate changes the ceiling
This is the one piece of physiology worth understanding, because it explains every premium product on the shelf.
The 60 gram wall
Your intestine absorbs glucose through a transporter that saturates at roughly 60 g per hour. Push more glucose in and it does not reach the muscle, it sits in your stomach. That is where bloating, cramps and the sudden emergency come from. It is a plumbing limit, not a willpower limit.
How fructose gets around it
Fructose uses a different transporter. Combine the two sugars and total absorption goes well past the glucose ceiling, which is why serious endurance formulas are built on a glucose to fructose ratio rather than glucose alone. Science in Sport, for example, publishes a 1:0.8 ratio and 40 g of carbohydrate per gel on its Beta Fuel product page, aimed at efforts beyond two hours.
Practically: below 60 g per hour, any gel works. Above it, only a dual-source formula is worth the money. Everything else is flavour.
When to take them, before and during
The first gel goes in early
Take gels in anticipation, never in reaction. Absorption takes 15 to 20 minutes, so if you wait until you feel the wall, you are already twenty minutes too late. In a marathon the standard marker is kilometre 8 to 10, long before anything feels wrong.
Always with water
Drink 100 to 200 ml with every gel. A concentrated sugar load without water pulls fluid into the intestine and produces exactly the problem you were trying to avoid. Line each gel up with an aid station rather than taking it between two.
The 15 to 30 minute trap before the gun
Avoid taking a gel in the 15 to 30 minutes before the start. The insulin response can drop your blood sugar at the worst possible moment. Either take it five to ten minutes before, or wait until the first kilometre. This is one of those details nobody mentions until it happens to you.
What to check on the label
Four numbers tell you almost everything, and none of them is the flavour.
- Carbohydrate per sachet: this is what actually feeds you. Products range from roughly 20 g to 50 g, which changes how many you carry for the same intake.
- The glucose to fructose ratio: if it is not stated, assume single source and cap yourself at 60 g per hour.
- Sodium: varies enormously between products. It matters if you sweat heavily or race in heat.
- Caffeine: present in some flavours and absent in others within the same range. Check before you take three in a row by accident.
Texture deserves a mention too. Some brands, Maurten among them, build their gels on a hydrogel matrix designed to carry the sugars through the stomach before releasing them. If your gut is the weak link in your racing, that technology is the one premium feature with a real argument behind it. If your gut is fine, it is money you can keep.
The homemade gel
No brand will tell you this, but you can make a perfectly decent gel for roughly a tenth of the price. For about 25 g of carbohydrate:
- 20 g of honey, which supplies most of the carbohydrate.
- 10 g of agave or maple syrup, which brings the fructose side of the dual source.
- A pinch of fine salt, replacing some of the sodium you lose sweating.
- A teaspoon of lemon juice, which cuts the sickliness of pure sugar.
Mix it, decant it into a small soft flask, and you have a training gel for pennies. The limits are real: the composition is less consistent, there is no hydrogel matrix, and you have a flask to manage on the run. But for long training runs it is entirely valid, and long training runs are where you consume most of your gels anyway.
Running energy gels FAQ
Do I need gels for a 10K?
No. Under 75 minutes of effort your glycogen stores cover the demand. If a gel helps you psychologically, take one, but do not expect a physiological effect. Spend the attention on pacing instead.
Gel with or without caffeine?
Caffeine reduces your perception of effort late in a race, which is genuinely useful. It can also irritate the stomach. Keep it for the last thirty minutes, and test it in training before you rely on it on race day.
Can I take two gels at once?
You can, and on an ultra with cold hands it is sometimes the practical choice. But you are stacking sugar on one absorption window, so only do it if you have rehearsed it. A gut that has never seen 80 g in twenty minutes will tell you about it.
How long do gels last once opened?
Treat an opened sachet as single use. The convenient alternative is a soft flask with two or three gels decanted into it, which also removes the litter problem that race organisers and World Athletics increasingly take seriously on course.
Do gels work for trail running?
Yes, but not on their own past four or five hours. Alternate them with real food and keep one very digestible gel in reserve for the end of the race, when nothing else will go down. That single reserve gel has rescued more finishes than any nutrition plan on a spreadsheet.
Here is the short version: work out your carbohydrate per hour first, take the first gel before you need it, always with water, and train your gut on the exact plan you intend to race. Do that and running energy gels stop being an expensive superstition and start being the thing that keeps your last ten kilometres intact. Plan it now, not on the start line!
Product figures checked on 19 September 2026 on the manufacturers’ own pages: Science in Sport and Maurten. Runningix sells none of these products and received nothing from the brands mentioned.