health-nutrition

Running nutrition comes down to one principle: fuel for the run you’re doing, not the run you wish you were doing. A 40-minute easy jog does not need a gel. A 20-mile long run absolutely does. Most of the stomach problems and bonks I’ve dealt with over the years came from getting that mismatch wrong.

Below I cover the carbohydrate targets in grams per hour, a marathon fueling strategy, and an honest comparison of the three gel brands I’ve put through full training blocks — Maurten, GU, and SiS.

Disclosure: Some links are affiliate links. As a partner of the brands mentioned, I may earn a commission from qualifying purchases at no extra cost to you. I manage type 2 diabetes while training, so I take fueling seriously — but this is my experience, not medical advice. Talk to your doctor, especially if you’re on medication that affects blood sugar.

The three windows: pre, during, post

Almost every fueling question maps onto one of three windows, each with a different job.

Window	Goal	What matters	Common mistake
Pre-run (1-3 hrs before)	Top up glycogen, settle the stomach	Carbs, low fiber, low fat	Eating too close, too much fat/fiber
During (while running)	Delay glycogen depletion	Water always; carbs only past 60 min	Gels on a 30-min jog, or nothing on a 3-hr run
Post-run (0-60 min after)	Replenish glycogen, repair muscle	Carbs + protein together	Skipping it after “just an easy run”

Most runners obsess over gels and neglect the bookends. Get the pre and post right and the during-run part mostly takes care of itself.

Pre-run nutrition

Timing: 1 to 3 hours before

Give yourself 1 to 3 hours between a real meal and a hard run. The closer to the run, the smaller and more carb-dominant the meal. A useful research-backed rule: aim for 1 to 4 grams of carbohydrate per kilogram of body weight in the 1-4 hours before harder sessions, scaled to the window. For a 70 kg runner that’s 70-280g of carbs.

What to eat

Keep it carb-forward and familiar. My default pre-long-run breakfast in Barcelona is toast with jam, a banana, and black coffee — about 90 minutes before I head out along the beach. That is maybe 80g of carbs, digests easily, and I’ve never had GI trouble with it. Oatmeal with honey, white rice with fruit, or a plain bagel all work.

The fasted-run question

Fasted easy runs are fine and useful for aerobic base — it connects to the Zone-2 thinking in our marathon training plan. But fasted runs are for easy, short efforts only. Never do a hard session or a long run fasted. You won’t get the adaptation benefit and you’ll train your body to run poorly.

What to avoid

In the last 2-3 hours, hold off on high-fiber foods (raw veg, beans, bran), high-fat foods (fried anything, heavy cheese), and spicy food. Fiber and fat slow gastric emptying — the opposite of what you want before bouncing up and down for an hour.

During-run fueling

This window gets over-thought. The carb targets by duration are well-established.

Under 60 minutes — water only. Your glycogen stores can carry you. Beginners reaching for gels on a 5K jog are wasting money and risking stomach trouble.

60-120 minutes — 30-60g carbs per hour. That’s roughly one gel every 30-45 minutes, or a bottle of sports drink, or a couple of energy chews. This covers most long runs in a marathon block.

Over 2 hours — up to 90g carbs per hour, with glucose:fructose. Pure glucose tops out at about 60g per hour because that’s the maximum your gut can absorb through a single transporter. To get past it you need a glucose:fructose mix in roughly a 2:1 ratio, which uses a second absorption pathway. This is the science behind Maurten, SiS Beta Fuel, and the newer high-carb mixes.

Whatever your hourly target, break it into doses: one gel every 30-45 minutes, starting the first around 45 minutes in. Don’t wait until you feel flat — by the time you feel a bonk, you’re 20 minutes behind.

Marathon fueling strategy

A marathon is a fueling problem disguised as a running problem. You carry roughly 90-120 minutes of stored glycogen, and most people run a marathon in 3.5 to 5.5 hours. Skip the refueling and you hit the wall around mile 20.

For a marathon I aim for 60-90g of carbs per hour — a gel every 30-40 minutes from the first hour. I also do a proper carb load in the 48-72 hours before: not the old-school pasta dinner, but 8-10g of carbs per kg of body weight across those final days with reduced training. The full taper-week version is in the marathon training plan.

Caffeine is the most evidence-backed performance aid in endurance sport: 3-6mg per kg of body weight (200-400mg for most runners), taken 45-60 minutes before a hard effort. Most marathoners use a caffeinated gel around mile 16-20. If you train with caffeine, race with it; if you don’t, don’t start on race day.

Train the gut. This is the most underrated part of marathon fueling. If you’ve never taken 60g of carbs per hour, doing it for the first time on race day is a port-a-loo emergency. Across the last 8 weeks of a block, practice your race-day fueling on every long run — same gels, same timing, same hydration. The race-day notes in my Helsinki Marathon review cover what actually happens on the day.

Energy gels compared: Maurten vs GU vs SiS

These are the three brands I’ve run full training blocks with. Here’s the honest head-to-head.

Brand	Carbs per serving	Texture	Caffeine option	Price per gel (approx)	Best for
Maurten	40g (Gel 160)	Thick hydrogel, jelly	No (separate Caf100)	~$4.50	High-carb racing, sensitive stomachs
GU Energy	20-23g	Classic syrup	Yes (multiple)	~$1.75	Everyday fueling, flavor variety, budget
SiS GO	22g	Liquid, isotonic	Yes	~$2.25	Easy on the stomach, no-water-needed gels

All three work. The differences are about texture, carb density, and price. The magic is taking the right amount, at the right time, that your gut tolerates.

Maurten deep-dive

Maurten built its reputation on hydrogel technology — the gel mixes alginate and pectin with the carbs, so when it hits your stomach’s acidity it forms a hydrogel that passes through to the intestine before releasing the carbs. The practical effect: less sloshing, less nausea, and more carbs down per hour. Their Gel 160 packs 40g of carbohydrate in a single sachet, roughly double a standard gel.

Maurten is what you see on the biggest stages — Eliud Kipchoge’s sub-2-hour attempt, the Major marathon circuit, and the Barcelona Marathon elite fields I’ve watched along the beachfront. The texture is polarizing: thick, almost jelly-like, neutral rather than sweet. The downside is price — at roughly $4.50 per gel, a marathon’s fueling can cost $25-35. I reserve Maurten for race day and key long runs.

GU deep-dive

GU is the original energy gel — around since 1991 and still the default at most aid stations. A standard GU has 20-23g of carbs (maltodextrin and fructose, so you get the dual-transport benefit), plus added amino acids and electrolytes.

What GU does better than anyone is flavor and accessibility — 20+ flavors, caffeinated and non-caffeinated, sold everywhere. The texture is the classic gel-syrup most runners first learn on. At roughly $1.75 per gel, they’re the most affordable everyday option, and the GU Electrolyte Brew pairs cleanly for hydration. If you’re new to fueling or on a budget, start here.

SiS deep-dive

Science in Sport (SiS) takes a different approach with their GO Isotonic gel — 22g of carbs in a thinner, liquid form that’s isotonic, so it absorbs without extra water. That makes them the easiest gel to take when you can’t get to a bottle, and a lot of runners find the lighter texture sits better than thicker gels.

The choice of the Ineos Grenadiers pro cycling team, SiS has a strong following among marathoners who struggle with gel stomach. The trade-off: each gel has fewer carbs, so you take more of them — roughly one every 20-30 minutes. For high-carb efforts (90g/hr), SiS makes a Beta Fuel line with the 2:1 glucose:fructose ratio.

Post-run recovery

“That fueling was harder to get right than the workouts. Eating enough of the right things around training — without undoing the deficit — took more thought than the actual running and lifting.”

That line is from my type 2 diabetes comeback story, and it’s just as true for the post-run window as the pre-run one. This is where the adaptation happens — glycogen gets replenished, muscle damage repaired, and the next session gets easier or harder depending on how seriously you take this.

The 30-minute window

There’s a window of roughly 30-60 minutes after a hard or long run where your muscles rebuild glycogen faster than normal. For anything over an hour, or any quality session, use it. For a 30-minute easy jog, don’t overthink it — just eat normally.

Protein plus carbs together

The recovery combination is protein and carbs together, not one or the other. A useful target is roughly 20-25g of protein and 60-80g of carbs in that first recovery meal — a carb-to-protein ratio around 3:1 or 4:1. Practical versions: cereal with milk and a banana, a chicken sandwich, chocolate milk (yes, really — the ratio is close to ideal), or a recovery shake.

Rehydration

If you ran over an hour or in the heat, you lost meaningful fluid and sodium. Weigh yourself before and after a few long hot runs to learn your sweat rate — anything over 2% body weight loss starts to hurt performance. Drink to replace, and include sodium. For recovery electrolytes I keep Amazon-available options like Nuun or Liquid I.V. in the cupboard.

A diabetes-specific note on blood glucose

One paragraph, because it’s the most honest thing I can add here: as someone managing type 2 diabetes while marathon training, the post-run window is where I pay closest attention. A hard long run can drop my blood glucose significantly for hours, and the standard “refeed with carbs immediately” advice has to be balanced against not spiking it on the rebound. I time recovery carbs to my glucose response rather than the clock, and test more frequently after long efforts. If you’re in a similar boat — type 2 diabetes, insulin, a GLP-1 like Mounjaro — your fueling has to be built around your glucose data, not a generic guide. The full version is in the comeback post, and you should be working with your doctor on this.

Hydration and electrolytes

Water vs sports drink. For runs under an hour, plain water is enough. Past an hour, especially in heat, you want a drink with both carbs and electrolytes — it handles the fueling target and sodium replacement in one go.

Sodium. Sweat contains 300-700mg of sodium per liter, and salty sweaters lose more. A general target is 300-600mg of sodium per hour during longer efforts, more in extreme heat. Most gels include some sodium but rarely enough — which is why sports drinks and electrolyte tabs (Tailwind is a clean all-in-one; electrolyte tabs from Amazon work well for shorter runs) earn their place.

Heat: the Barcelona context. The Barcelona summer is brutal — I’ve done long runs where it was 28°C and humid at 8 a.m. along the beach. Heat multiplies fluid and sodium needs a lot. Two lessons: run early, and start hydrating the day before a long hot effort, not the morning of. The Helsinki Marathon review covers race-day hydration in different conditions.

FAQ

Can I use real food instead of gels?
Yes, for easier efforts and shorter long runs. Bananas, dates, jam sandwiches, and boiled potatoes all work. Gels exist for carb density — a Maurten Gel 160 gives you 40g of carbs in 70ml, the equivalent of nearly two bananas. For races and hard long runs, gels win. For a 90-minute trail jog, real food is fine.

How many gels do I need for a marathon?
For most runners aiming for 60-90g of carbs per hour over a 4-hour marathon: roughly 10-14 standard gels, or 6-8 high-carb gels like Maurten. Practice the full amount in training. The exact plan is in the marathon training guide.

What do I do if gels upset my stomach?
First, check timing — gels need water, usually 150-250ml per gel. Second, lower your hourly carb rate and train your gut up over weeks. Third, switch formats: SiS GO is isotonic and easier for many, and Tailwind in your bottle sidesteps the gel-stomach problem for some. If it persists, move to a 2:1 glucose:fructose mix.

Should a beginner use energy gels?
For 5K training and runs under an hour, no — you don’t need them and they add stomach risk for no benefit. (See the gear thinking in our running shoes pillar.) Once your long runs pass 75-90 minutes, gels start to earn their place.

Do I need protein right after an easy run?
Not urgently. The 30-minute window matters most after hard or long sessions. After a 30-minute easy jog, just eat your next normal meal with good protein. Protein timing genuinely matters after intervals, long runs, and races — that’s when the 20-25g-within-an-hour rule is worth following.

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If you take one thing from this guide: fueling is not about the brand, it’s about matching intake to the run. Figure out your carb-per-hour target, pick the format your stomach tolerates, practice it in training, and don’t overthink the rest. The boring version — toast and jam before, one gel every 40 minutes during, a real meal after — is the one that works.

To go deeper, the fueling here slots into the 16-week marathon training plan — and pairs with the best On running shoes for a marathon if you’re race-day planning. For the wider gear field, the best running shoes and best GPS running watches pillars cover the rest of the kit. For the gels, start with Maurten for race day, GU for everyday value, and SiS if you want an easier-on-the-stomach option.

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