Common mistakes runners make with their nutrition and how to avoid them

Most running nutrition mistakes are not exotic. They are the same ten errors, made by experienced runners as often as beginners, and each one costs you minutes rather than seconds. Here they are, with the specific fix for each.

None of this requires a dietitian or a lab. It requires doing the arithmetic once and then rehearsing it on your long runs.

1. Waiting until you feel empty before the first gel

What goes wrong. You feel fine at 40 minutes, so you skip the first gel. By the time you notice you need one, you are already behind, and carbohydrate takes five to fifteen minutes to arrive. You spend the rest of the race chasing a deficit you cannot close.

The fix. Take the first serve at 30 to 45 minutes, whether you feel like it or not, then hold the interval. Set a recurring alert on your watch by time, not distance. At 4:00 pace a gel every 45 minutes lands around 11km. At 6:00 pace it lands around 7.5km. Distance markers will drift, a timer will not.

2. Guessing your hourly carbohydrate number

What goes wrong. Most runners carry the number of gels that fit in their belt, rather than the number their race requires. Then they run out at 32km or bring three home unused.

The fix. Current guidance for marathon running sits at 60 to 90 g of carbohydrate per hour, with well trained athletes on high carb protocols pushing towards 120 g. Pick your target, then divide by what your gel carries.

A four hour marathon at 60 g per hour is 240 g in total. Count the sachets before you leave the house, then carry one spare. The full working is in our guide to energy gels for marathon running.

3. Never practising at race intake

What goes wrong. You train on one gel per long run, then take four per hour on race day. Your gut has never seen that volume and it objects, usually somewhere around 28km.

The fix. Gut tolerance is trainable. Most runners who report stomach trouble have simply never rehearsed at race intake. Take your full hourly target on at least three long runs in the build, and treat each one as a dress rehearsal for flavour, texture and logistics as much as for pace.

4. Under fuelling the easy days

What goes wrong. Runners fuel the sessions that feel hard and skip food around the ones that feel easy. Over a training block that adds up, and the first thing to go is the quality of the hard sessions, not the easy ones.

The fix. Eat around every run, including the easy ones. If a morning run happens before breakfast, a serve of UCAN Energy Powder mixed cold 30 to 45 minutes out covers it without sitting heavy. If any of this raises questions about your own intake, a sports dietitian is the right person to ask.

5. Treating every electrolyte product as interchangeable

What goes wrong. The word electrolyte on the front of a pack tells you nothing. Sodium per litre across the category runs from around 400 mg in a supermarket sports drink to 2,000 mg in a salt forward mix. Buy the wrong end of that range for your sweat rate and you either cramp or you cannot drink it.

The fix. Convert sodium to a per litre figure so you can compare brands with different serve sizes, then check whether magnesium and calcium are in the formula at all. The thirty second version is in our guide to choosing an electrolyte drink.

6. Not counting the sodium already in your gels

What goes wrong. You set an hourly sodium target from a sweat test, then meet it with your drink alone, forgetting the gels are contributing too. Or the reverse: you assume your gels have sodium in them and they carry 10 mg.

The fix. Add it up. Sodium across gels ranges from 10 mg to 200 mg per sachet, a twenty fold difference that is rarely on the front of the packet. Work out your own number first with the sweat rate test in our hydration guide, then build the total from everything you are carrying.

7. Taking a thick gel without water

What goes wrong. A concentrated sugar gel taken dry has to be diluted before your body can absorb any of it, so it pulls fluid into your gut. That is the sloshing, the bloating and the cramping, and it usually shows up twenty minutes after the gel rather than immediately.

The fix. Unless you are on an isotonic or a slow release gel that is formulated to go down dry, take it just before a water station. Two or three good mouthfuls is enough. If you keep having this problem, the format is the issue rather than your technique, and a sugar free gel removes the variable entirely.

8. Stacking caffeine without counting it

What goes wrong. Coffee before the start, four caffeinated gels through the race, and a cola at an aid station. You are past 350 mg without having planned a single milligram of it, and the last hour feels jittery rather than sharp.

The fix. The evidence based range is 3 to 6 mg per kilogram of body weight for the whole day, coffee included. For a 70 kg runner that is 210 to 420 mg. Subtract your coffee first, then work out how many caffeinated gels fit in what is left. The arithmetic is worked through in our caffeine gel guide.

9. Trying something new on race day

What goes wrong. The expo hands out samples, a friend recommends a brand, the aid station carries something you have never used. All of it is a gamble taken at the one moment you cannot afford to lose.

The fix. Carry your own. Course nutrition is a brand you may not have trained with, handed to you at a pace you did not choose. Buy single sachets and test flavours in your build rather than on the start line. A flavour you enjoy at 5km can turn your stomach at 35km, so carry one fruity and one neutral.

10. Skipping the hour after you stop

What goes wrong. You finish, you stretch, you drive home, and you eat two hours later. The next session is compromised before you start it, and on a heavy training week that compounds across days rather than showing up on one.

The fix. Carbohydrate and protein within the hour after you stop. UCAN Energy + Protein does both in one serve and travels in a bag, which matters more than the formula because the mistake is almost always logistics rather than knowledge.

Build the plan once, then stop thinking about it

Every mistake on this list comes from making a decision on the run rather than before it. A plan you have rehearsed twelve times becomes the one predictable thing on a chaotic race morning, and it frees your attention for pacing.

Write it down: what you take before the start, the interval on your watch, how many sachets, where they sit, and what goes in within the hour after. Then run it on two long sessions before you race it.

Frequently asked questions

Guidance here is general and not individual advice. Carbohydrate tolerance, sweat rate and sweat sodium concentration vary widely between individuals. Test any change to your fuelling in training before you race it. If you have specific concerns about your intake or your training load, speak to a sports dietitian.

The kit that fixes most of them

Four products, and which mistakes on this list each one solves.

Fixes 1, 2, 7 and 9

UCAN EDGE Energy Gels

19 g of slow release carbohydrate, zero sugar, thin enough to swallow without a bottle. Nothing concentrated for your stomach to dilute at 30km.

Shop EDGE →

Fixes 5 and 6

UCAN Hydrate Electrolytes

Five electrolytes with the sodium figure published per serve, and zero carbohydrate, so it never interferes with your fuel arithmetic.

Shop Hydrate →

Fixes 4

UCAN Energy Powder

The pre session serve for runs that start before breakfast. Mix cold, drink 30 to 45 minutes out, no stimulants.

Shop Energy Powder →

Fixes 10

UCAN Energy + Protein

Carbohydrate and protein in one serve for the hour after you stop. Travels in a bag, which is usually the whole problem.

Shop Energy + Protein →

Not sure which flavour you can still drink at hour three? Every one is available as a single sachet. Test it on a long run before you buy a box.

Go deeper on each fix

Four guides that go further than a bullet point.