Beat the Bonk

Nutritional Strategies for Endurance Athletes

Welcome, fellow runners and fitness enthusiasts. Every endurance athlete knows the feeling.

Legs moving well, breathing under control, pace comfortable enough. Then somewhere around the halfway mark, things start to come apart. Pace drops. Legs go heavy in a way that has nothing to do with muscle soreness. You can't hold a thought. You start wondering, seriously, why you signed up for this.

That's the bonk.

It can arrive gradually or seemingly out of nowhere, one minute you're fine, the next you're empty. Nutrition is a big part of whether it happens to you.

Training builds the fitness. Fuel is what lets that fitness actually show up when the distance gets long. And the good news is that sports nutrition doesn't require a cupboard full of powders and gadgets. You need to understand what your body is burning, feed it enough carbohydrate, drink sensibly, and rehearse the plan before race day.

There's also going to be trial and error. Accept that now and it'll bother you less later.

What is the bonk, actually?

"Bonk" describes a severe drop in performance caused by running low on carbohydrate during long exercise.

Your body has a few ways to make energy, but carbohydrate becomes the main event as intensity climbs. It's stored as glycogen, mostly in muscle and liver, and that store is finite. A well-fed runner starts a long session with a decent tank, but it drains as the miles go by. If you're not replacing carbohydrate during exercise, the gap between supply and demand eventually catches up with you.

Signs include:

• Energy dropping suddenly or slowly
• Legs that feel heavy or weirdly weak
• Pace falling off
• Trouble concentrating
• Irritability
• Fatigue that feels different from normal tiredness
• An urge to just stop
• Clumsiness, poor coordination
• Every kilometre starting to feel like a fight

One caveat worth flagging: feeling awful late in a run doesn't automatically mean you're bonking. Heat, dehydration, muscle fatigue, bad pacing, poor sleep, and accumulated training load can all wreck a session on their own. The classic bonk is specifically tied to depleted glycogen and not enough carbohydrate coming in during exercise.

Once you're in it, climbing back out takes time. Avoiding it in the first place is a lot easier.

Carbohydrate is your friend, not your enemy

Carbs get a bad rap in general nutrition talk. Endurance athletes need to unlearn that.

During a long run or ride, carbohydrate is the fuel your body can access fastest. Muscle glycogen in particular gets broken down directly for the muscles doing the work.

That doesn't mean eating pasta by the kilogram every day. Your carbohydrate needs track your training; a short, easy recovery jog barely registers, but a two- or three-hour long run is a completely different demand, and so is a hard interval session followed by another tough one the next morning.

The mistake I see a lot: eating the same way every single day regardless of what the training actually asked of the body. A rest day and a 30 km long run are not the same request.

Eat enough before the long session

The simplest way to lower your bonk risk is to start the run properly fuelled.

Your pre-run meal needs to be carbohydrate you can actually digest without drama. Some options that tend to work:

• Oats with banana and yoghurt
• Toast with honey or jam
• Cereal with milk and fruit
• Rice with a bit of lean protein
• A banana and a bagel
• Potatoes the night before, if you're running early

The specific food matters less than finding what your stomach tolerates. Someone who's fine eating a big bowl of oats three hours out might feel sick eating the same bowl 45 minutes before the gun goes off. Timing is part of the equation, not an afterthought.

For a longer session, eat your main meal several hours ahead if you can. Training early? A smaller snack - banana, toast with honey, small bowl of cereal, is often enough.

Test this in training. Race morning is not the time to discover a new breakfast doesn't sit well.

The night before matters too, but not the way people think

There's a strange obsession with the pre-race pasta feast, as if one meal can bank you an infinite tank of energy. It can't.

Carbohydrate loading is a real, specific strategy, increasing intake over the days before an event while cutting training, mainly for races over roughly 90 minutes. For an ordinary weekend long run, you don't need a carb-loading ritual.

A normal evening meal with rice, pasta, potatoes or bread, plus vegetables and some protein, is enough to top up glycogen. Keep it familiar. Race week is the wrong week to test a new curry.

Fuel during the run

This is where a lot of runners fall down.

Breakfast goes fine. The run starts fine. An hour in, still fine. Then the wheels come off.

For anything longer than about 60 to 90 minutes, taking carbohydrate during the exercise itself helps maintain performance and delays fatigue. Current guidance points to roughly 30 to 60 grams of carbohydrate per hour for prolonged endurance exercise, and some well-trained athletes push toward 90 grams an hour in very long or demanding events.

More isn't automatically better, though. Your gut has to be trained for this just like your legs. Jump straight to 90 grams an hour with zero practice and your stomach will let you know exactly how it feels about that decision.

Start with an amount you tolerate; say, 30 grams an hour on long runs and build from there if it feels okay.

Where the carbohydrate actually comes from

Plenty of options.

Gels are popular because they're small and easy to carry, usually 20 to 30 grams of carb each, though it varies by brand. Beyond that:

• Sports drinks
• Chews
• Energy bars
• Jelly sweets
• Bananas
• Dried fruit
• Homemade carb drinks
• Jam sandwiches, cut small

There's no prize for buying the most expensive product on the shelf. What matters is the carbohydrate amount, whether your stomach handles it, and whether you can actually carry and use it mid-run.

A 30 km training run is a good place to experiment. Try a gel at 45 minutes on one run. Try a gel at 30 minutes plus another later on the next. Notice how your energy, stomach and general mood respond. Write it down if you need to, you'll land on a pattern that works for you.

Don't wait until you feel empty

One of the biggest mistakes out there: waiting until you're tired before you eat. By then the deficit is already building.

Fuel throughout the session, not as an emergency fix once things go sideways. If your long run is going to take two and a half hours, plan the carbohydrate intake before you leave the house, and take it on a schedule rather than waiting to feel hungry.

Smaller, regular amounts tend to sit better than a desperate handful of gels crammed in during the last hour.

Train your stomach like you train your legs

Your gut needs training too. Some runners handle carbohydrate during exercise easily. Others get bloating, nausea, cramps, that unpleasant sloshing feeling.

It's partly what you consume, partly how much. Training the gut means gradually exposing it to carbohydrate during exercise, start conservatively, use long runs to rehearse race nutrition, try the same products at similar points in the run.

If a product keeps causing trouble, drop it. It doesn't matter how much your running partner swears by it. You're allowed different preferences.

Hydration matters too

Carbohydrate gets most of the attention when people talk about bonking, but fluid loss plays its own role.

Sweat rate varies wildly between people. One runner finishes a long session looking barely damp; another is drenched in the exact same conditions. Weather changes everything too, a cool winter morning in the Western Cape asks a lot less of you than a hot summer afternoon over the same distance.

Don't drink a fixed amount just because someone on social media insists everyone needs the same quantity per hour. Your sweat rate is yours. One practical way to estimate it: weigh yourself before and after a session, accounting for fluid consumed and any bathroom breaks. A meaningful drop in body mass tells you something useful about your fluid loss.

Electrolytes, briefly

Sodium is the one endurance athletes usually focus on, since it's lost in sweat and matters for fluid balance and muscle function. Sweat sodium concentration varies a lot person to person, some people finish a run with visible salt crust on their kit, others show nothing at all.

There's no single magic number that fits everyone. For long or hot races, an electrolyte drink or other sodium source can help. But don't assume every cramp is a sodium problem, cramping is messy and involves fatigue, pacing, and neuromuscular factors too.

And drinking huge amounts of plain water isn't automatically safer. It can dilute blood sodium and contribute to exercise-associated hyponatraemia, which is a genuine medical emergency in severe cases.

Overhydration is a real risk, not a myth

Some athletes are so scared of dehydration that they drink constantly through an entire race, and that habit can cause the exact problem above: blood sodium drops if fluid intake outpaces sweat loss by enough.

The fix isn't to drink less out of fear. It's to stop treating hydration like a competition and drink according to conditions, your own needs, and a plan with some flexibility built in, more fluid on a hot day, less on a cool one, adjusting as an ultra-stretches into its later hours.

Protein has a job too

Carbohydrate gets you through the session. Protein handles recovery and keeps muscle tissue intact, and it's easy for endurance athletes training frequently to underrate how much they actually need.

You don't need a protein shake the second you finish running. A normal meal does the job - eggs, milk, yoghurt, chicken, fish, lean meat, beans, lentils, tofu, cottage cheese, whatever you actually like eating.

Pairing carbohydrate with protein after a hard session supports recovery. Yoghurt with fruit and oats. Eggs on toast with fruit. Rice, vegetables and chicken. Nothing here needs to come in a shiny packet.

Recovery starts the moment you stop

The run is done. Now what?

Some athletes finish a hard session, spend the next four hours drinking coffee, and tell themselves they'll eat "later." Meanwhile the body has real work in front of it, glycogen to replace, muscle to repair, fluid to replace.

You don't need to hit some mythical five-minute window. But eating a proper meal or snack within a reasonable stretch after training is sensible, especially with another hard session coming soon. If tomorrow is a rest day, you've got more slack than someone doing two demanding sessions inside 24 hours.

Fibre and fat need a little planning, not elimination

Both are healthy and both stay in your diet. Timing is the only thing that changes.

A huge high-fibre meal right before a marathon is a good way to spend the race looking for a toilet instead of chasing a personal best. Heavy, fatty meals digest slowly and can leave some runners feeling sluggish too. Many athletes trim high-fibre and high-fat foods in the final meal or two before an important race, not for the whole week, just around the edges of it.

Everyday eating is the actual foundation

Race-day nutrition gets all the attention, but what you eat on an ordinary Tuesday matters more over time.

If you're chronically under-eating, no number of race-day gels fixes that. Training burns energy, and the body needs enough food to cover training, recovery, and just being a person day to day. A sensible plate for an endurance athlete includes fruit and vegetables, whole grains, potatoes and other carb-rich foods, dairy or an alternative, lean protein, beans and lentils, nuts and seeds, healthy fats, enough fluid.

Exact amounts depend on you, someone training for a marathon needs a lot more than someone running three easy times a week for general fitness.

Don't copy someone else's plan

Your training partner swears by a particular gel. Your coach likes a different sports drink. A pro athlete on TV is taking in more carbohydrate per hour than you'd think possible. None of that means it's right for you.

Body size, training history, sweat rate, pace, weather, stomach tolerance, race duration, all of it shapes what works. Treat other people's advice as a starting point, then go test it yourself.

A simple plan for your next long run

If your fuelling has been hit-or-miss, don't overhaul everything at once. Keep it simple: eat a familiar carb-based meal beforehand, take enough fluid for the conditions, and if the run will go past 60 to 90 minutes, carry a carbohydrate source and start using it before you feel wrecked.

Pay attention to your stomach. Afterward, eat something with both carbohydrate and protein. Then write down what happened. How did you feel at 10 km? At 20? Did energy hold steady? Was your stomach okay? Were you thirsty? Did you actually take enough fuel?

That log is worth more than any plan you copy off someone else.

Building a marathon or ultra strategy

Whatever you plan to do on race day, 60 grams of carbohydrate an hour, a specific gel, drinking at every aid station, rehearse it during long runs first. Race day is not the place to test anything new.

Ultras raise a separate problem: taste fatigue. After several hours, another sickly-sweet gel can start to feel genuinely repulsive. Having a few different carbohydrate sources on hand helps; gels, sports drink, bananas, small bits of real food. Some runners crave savoury food late in an ultra. What works varies a lot, so again, test it in training rather than finding out at hour fourteen.

Put numbers on your plan

"Eat when I feel hungry" isn't really a plan. Something closer to a real one looks like this:

Before the race: familiar carb-rich breakfast, fluids on board. First hour: start carbohydrate intake early, don't wait. Each hour after: stick to the carb range you've already practised. Fluids: drink based on conditions and your own needs, not a generic rule. Sodium: bring in a source when the race or the weather calls for it. After finishing: replace fluids, eat something with carbohydrate and protein.

Keep the numbers personal. If you've never fuelled during exercise before, start low and build. If you're already comfortable with it, you can push the intake up gradually and see what your gut allows.

Bad runs teach you something

A failed long run stings, but it's also data.

Maybe you skipped breakfast. Ran faster than planned. Held off on the first gel until you were already struggling. Drank too much water. Underestimated what a hot day would cost you.

Write it down. Change one or two things on the next long run and see what happens. Do that for a few months and you'll understand your own body far better than any generic plan could tell you.

When it's time to get professional help

Most recreational endurance athletes can sort out their fuelling by learning the basics and sticking with it. But persistent gut problems, unexplained fatigue, repeated dizziness, real weight changes, trouble eating enough, or worries about your relationship with food are reasons to talk to a sports dietitian or doctor rather than keep guessing. That's especially true if you're building toward an ultra or a multi-day event, where a dietitian can help map out carbohydrate, protein, hydration and race-day fuelling in real detail.

The goal is steady energy

None of this needs to be complicated. Enough energy to train well. Enough carbohydrate available when the session stretches long. Fluids replaced sensibly. Food your stomach can actually handle. And a plan you've already tested before race day arrives.

The bonk feels dramatic when it hits, one minute you're cruising, the next the road looks twice as long and every hill takes it personally. So don't wait for race day to find your limits. Use your long runs for that. Practise the breakfast, test the gels, try different drinks, figure out how much carbohydrate your gut can actually take, watch how weather changes things, keep an eye on your energy.

Small adjustments add up. And when race day comes, you'll have something better than hope, you'll have a plan you already know works.