Every marathoner knows that the wall isn’t a myth. It’s a physiological and physical event: when your body’s glycogen stores deplete, your pace drops, and the last ten kilometres feel twice as long as the first thirty. The difference between surviving that moment and maintaining control is almost always nutrition.

When I ran the Lisbon marathon in late October, I had six months of training behind me – and had tested just about every energy gel imaginable. Half of them I couldn’t even open while running (a rookie mistake, I know, but far more common than I ever thought), and others tasted so awful I nearly threw up before the carbs had a chance to do their job.

As I’ve learned the hard way, finding the right type of fuel is a process of trial and error. I’ve done my research so you don’t have to and can avoid at least some of the stomach cramps ahead. Here’s all you need to know about fueling for a marathon, be it your first or 10th.

First off, why do we need fuel?

As it turns out, our bodies store glycogen (its main carbohydrate fuel) in muscle and liver tissue, but only enough for about ninety minutes of sustained running. Once those reserves fall, performance usually drops sharply.

According to research, endurance athletes experience a 20–25% decrease in output when glycogen levels are halved. You can feel it happen: the legs that felt light and rhythmic start to stiffen, your stride shortens, and your concentration slips.

This is what runners mean when they talk about “the crash” or “hitting a wall.” As glycogen disappears, the body switches to burning fat for energy and while fat is abundant, it’s slow to convert into usable fuel. The result is a kind of power outage: your muscles still move, but they don’t have the speed or snap they did before.

Ingesting carbohydrates during prolonged exercise prevents this decline by keeping blood glucose stable and sparing stored glycogen. The consensus among official experts is that marathon runners should consume 60–90 grams of carbohydrate per hour, ideally from a mix of glucose and fructose to maximise absorption. The higher end of that range suits faster, well-trained athletes; most first-time marathoners perform best closer to 60 g/h.

So, what kind of gels and chews do you need?

When it comes to gels and chews, you can’t just grab whatever’s on the shelf at your local Decathlon (I wish that were the case!). You need something that gives you energy without upsetting your stomach, tastes decent enough to ingest at kilometre 35, and, crucially, that you can open with sweaty hands while on the move.

Some gels are thick like syrup, others go down more smoothly with a sip of water. Chews can be a good alternative if you prefer something to bite into, but they should be soft enough not to feel like a jaw workout.

I’ve tried most of the big names out there to train for my marathon – from GU and SIS to High5- and they all have their pros, but mostly, quite a few cons. So, I quickly became drawn to Precision Fuel & Hydration for a variety of reasons.

Firstly, the gels don’t really taste like anything, as they have no artificial flavourings. This, believe it or not, is a massive pro. Most gels are super salty or super sweet (or both), and just taste off, which immediately makes me a bit nauseous. The chews do have flavours (mint or lemon) but again, quite mild. They are a bit like Turkish delight bites.

There’s also the trust element for me – sports brands founded by sportspeople are just about 1000x more credible than others. And that’s the case with Precision Fuel & Hydration.

Its founder, Andy Blow, was a former triathlete with a Sports & Exercise science background. After years of cramping, struggling and underperforming in the heat, he partnered with surgeon-scientist Dr Raj Jutley to explore the wide individual differences in sweat rate and sodium loss. So you know they’re credible.

And last but not least, I really do appreciate that there’s a clear educational component to this brand. You can tell it’s just not about product for profit: they’re as passionate about running and performance as one can get, and very keen to share knowledge. You’ll find plenty of guidance in their Knowledge Hub online, but the company also does in-person heat training, sweat tests, and other tests in their Performance Lab in Dorset, UK.

How I fuelled for the Lisbon marathon

Now, there’s no miracle. Whatever brand you go for, the golden rule is to train with it first. The body behaves differently when it’s under pressure. Blood moves away from your stomach to feed your working muscles, digestion slows, and suddenly that “extra boost” sits in your gut like wet cement and you’re desperately looking for the nearest toilet.

Science shows that regular fueling practice increases the gut’s ability to move glucose and fructose into the bloodstream, so you get more useable energy and fewer stomach problems.

I’m by no means an expert but did follow expert advice and had one pack of chews just before the start of the race, then a gel pack every 10km (km 10, 20, and 30-ish). That combo worked really well for me – steady energy (as much as you can have) and not a lot of stomach drama. I love that you can open the pack quickly despite the sweaty hands and rain (it was pouring).

The gels, chews, and drink mixes are all fixed in composition. They are typically 30g of carbs per gel, or 500 mg / 1000 mg / 1500 mg sodium per litre for hydration mixes. But you can (and are encouraged to) combine them according to your sweat rate, sodium loss, and race conditions.

Another key point: hydration and sodium balance

Fuel alone won’t save you if you’re running dry. Every step of a marathon depends on blood flow, temperature control, and the body’s ability to move nutrients where they’re needed – and all of that relies on hydration. When fluid levels drop, blood thickens, heart rate climbs, and even an easy pace starts to feel like an uphill battle.

Everyone loses a different mix of water and sodium through sweat, and we’re all different. Some runners can cruise on plain water; others need electrolytes just to keep their muscles firing properly. Most research suggests 500–750 ml of fluid per hour, and 500–1,000 mg of sodium per litre, roughly one tablet or sachet per 500 ml. Precision Fuel and Hydration also have their own energy drink mixes and hydration tablets.

I took one tablet before leaving my accommodation and dropped another into the water bottle I carried throughout the run. Most marathons provide electrolyte stations along the course, so you can usually rely on those, but I prefer to bring my own and know exactly what I’m taking.

During the Lisbon Marathon, the official energy gel station didn’t appear until around kilometre 38 — far too late in the race to be much help — so it’s worth packing your own gels to stay fuelled earlier on.

In short…

Beyond the numbers, it’s about confidence. Practising means you know exactly what sits well, what doesn’t, and how often you need to take something before the wheels come off. The official marathon isn’t the time to find out that your favourite gel turns your stomach, or that you can’t open the packet with sweaty hands – you have more important things to worry about!

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