Sebastian Sawe ripped open a carbohydrate gel sachet and slurped it five minutes before the start of the 2026 London Marathon. Sixty minutes later, he inhaled another one before smashing through the two-hour marathon barrier.
Sawe might have been the first sub-two-hour marathon runner, but he’s certainly not the first to be powered by an energy gel. It’s estimated that over 70% of marathon runners use gels.
Long before energy gels were a thing, endurance athletes used all sorts of foods to fuel their athletic feats – from sugar lumps and coffee, to chocolate, beer, wine and even egg whites and brandy.
But from the 1970s scientists caught up with athletic practice. Research demonstrated that carbohydrates were effective in fuelling prolonged endurance exercise, with foods containing glucose and fructose (forms of sugar) proving to be the most effective fuels.
Thanks to decades of research, athletes today can use energy gels to provide fuel. These are precise, scientifically-calibrated carbohydrates in the form of maltodextrin and fructose blends encapsulated in a hydrogel.
But while these modern gels promise fast energy and improved performance, not all scientists are convinced they live up to the hype – and for many athletes, they come with uncomfortable side-effects.
So are gels really worth it, or should athletes stick to simpler, if less glamorous, sources of fuel?
Fuelling with energy gels
When we eat a meal, our bodies steadily breakdown the carbohydrates from food in the stomach. These carbohydrates are then gradually turned into glucose (simple sugar) in the blood.
Glucose is typically then transported to the muscles and liver where it’s stored as glycogen. This makes it easy for the body to access the stored energy when needed.
But our glycogen stores only last around 90 minutes before being depleted. Once it runs out, it can affect your performance. So many endurance athletes need to reach for carbs during long races and training runs to ensure they don’t run critically low on fuel.
In practical terms, energy gels offer a fast, convenient and concentrated source of carbohydrates that can be consumed mid-race without slowing down. Compared with whole foods, they’re easier to digest and more precisely dosed, helping runners maintain a steady energy supply.
However, this convenience comes at a cost. Gels can be expensive, some athletes find them unpalatable and they’re often associated with gastrointestinal discomfort – especially when taken in large amounts or without sufficient water.
Simpler options such as sports drinks or sugary foods may deliver similar energy, but typically lack the portability and precision that gels provide.
Research also shows there’s a lot of variation between available products. A survey of 31 gel product ranges (51 flavours total) across 23 brands found extreme variation in serving size, carbohydrate content, free sugars and especially osmolality (how concentrated a solution is). This has implications for how and when you should use gels and the effects they might have on your body.
Gels also may not really offer any additional benefits over other products, such as sports drinks.
A 2010 study found that gels and drinks deliver carbohydrates to the muscle at the same rate. This was later supported by a 2022 study which found drinks, gels and chews ingested were also no different in the benefits they conferred.
Gels can be a convenient way to fuel. frantic00/ Shutterstock
The only real advantage of using gels is their convenience, as they can be easily stored and consumed mid-run.
Gels may also have downsides. The most commonly reported issue is gastrointestinal distress, affecting around 10-20% of people according to one study.
Hydrogel drinks and products form gels in the stomach. The idea is that by encapsulating carbohydrates it helps to reduce the amount of water that crosses the intestinal barrier. This is supposed to prevent bloating and cramps. It’s also claimed that this enables more effective transport of carbs into the bloodstream.
But studies have not consistently shown better performance or less gastrointestinal distress compared with standard carbohydrates, even when calories are matched.
Concentrated gels make their way to small intestine but their sugar concentration is higher than surrounding blood and tissue so water is pulled into the gut. This may be why gels cause bloating and cramps if you don’t drink water alongside them.
How to use gels effectively
If your run is under 60 minutes, you probably don’t need gels.
If your run is 60-90 minutes or more, fuel before you feel empty. Aim for around 30-60g of carbs per hour.
Even if you don’t feel hungry, taking on small, regular amounts of carbohydrate – for example a few sips or a partial gel every 15–20 minutes – can help maintain energy levels before fatigue sets in
For very long races, you should aim for around 60-90g of carbs per hour. A mix of glucose and fructose appears to be most useful when intensity is high.
The most important thing is to test gels while training. Don’t use them for the first time on race day. This is to ensure your body can tolerate them and you know whether they effectively benefit your performance or not.
A small proportion of runners are much more prone to gastrointestinal issues, so if you experience this switching brands can make a big difference.
But if you find gels bother you no matter what, you could always reach for some of the foods endurance athletes used before gels were ever a thing – such as bread, fruit, sugar lumps, bananas, dates and rice cakes. Just make sure you practice with these in training as well to know how they work for your body.
While these foods work well when training at lower intensities, gels remain popular because they provide standardised dosing and are easy to consume at speed.
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