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Ask any coach what ruins more first ultras, fitness or food, and you'll get the same answer. It's the food. I've reviewed a stack of race files from my athletes, and when someone falls apart in the back half of a 50k or 100k, the story in the data is almost never "not enough training". It's a fuelling plan that fell over at hour four, and a death-march to the finish that no amount of vert in the training could have prevented.
I'm a running coach based in Sydney, and race nutrition is one of the topics I spend the most time on with my trail and ultra athletes. This guide is the fuelling system I build with them: how many carbs you actually need per hour, how to train your gut to accept them, an hour-by-hour worked example for a 50k and a 100k, and the adjustments that matter for racing in Australian heat. I've also run a full masterclass on this exact topic, you can watch the race nutrition masterclass here if you'd rather absorb it with a cuppa.
One thing before we start: none of this works if you first try it on race morning. Your nutrition plan gets built and rehearsed in training, then executed on race day. Nothing new on race day. Ever.
Here's the maths that every ultra runner needs to understand.
Your body starts a race with two fuel tanks of carbohydrate. Liver glycogen holds roughly 80–100g, call it 320–400 calories, about enough for 5km of running. Muscle glycogen holds 300–500g, roughly 1,200–2,000 calories, enough for about 22km. Add them together and a trained runner is carrying around 1,800 to 2,000 calories of stored carbohydrate. That's 90 to 120 minutes of continuous, solid effort.
Your race is going to take 6, 12, maybe 20-plus hours.
You also carry a huge amount of energy as fat, and at ultra intensities fat does a lot of the work. But fat is slow fuel. It produces ATP at about half the rate of carbohydrate, which is exactly why we do so much easy running in training, to get better at burning it. Even so, fat can't cover the whole bill on race day. Blood glucose has to fill the gap, and when your liver runs out of glycogen to prop up your blood glucose, you bonk. Hit the wall. Fall in a heap at the 38km checkpoint wondering why your legs stopped working.
The entire job of your ultramarathon nutrition plan is to keep topping up that system from the outside, hour after hour, so the wall never arrives.
The honest answer is: it depends on how long you're out there and how hard you're working. But there are firm numbers to build from.
Your gut has physical absorption limits. Glucose crosses into the bloodstream via a transporter called SGLT1, which maxes out around 66–72g per hour. Fructose uses a different doorway, GLUT5, good for roughly another 60g an hour. Because they use separate transporters, combining them lets you absorb more in total, which is why quality drink mixes and gels blend the two. The research points to a ratio of about 1:0.8 glucose to fructose as the sweet spot, with a practical ceiling somewhere around 90–120g of carbohydrate per hour.
Here's how I frame targets for my athletes:
| Race | Typical intensity | Carb target |
|---|---|---|
| Half marathon | High | 30–60g/hr (shorter races lean on stored glycogen) |
| Marathon | Moderate–high | 60–90g/hr |
| 50k ultra | Moderate | 60–90g/hr |
| 100k+ ultra | Low–moderate | 50–70g/hr, sustained for many more hours |
Notice the 100k number is lower than the 50k number. That surprises people. You're working at a lower intensity, so you're burning more fat and fewer carbs per hour, and your gut has to keep accepting food for 12–20+ hours rather than 6–8. Sustainability beats maximums every time.
You've probably seen the headlines. Elite marathoners taking 175g an hour. Pros at Western States hitting 126g an hour. Ironman athletes downing 28 gels. So should you be chasing 120g an hour too?
No. And this is where the science is worth a look.
A recent study had trained runners race a 53km trail course with 3,000m of vert, twice, on 90g per hour and on 120g per hour. The result? No statistical difference in performance. The 120g condition was actually slightly slower on average, and GI issues were considerably worse by the final loop, mostly upper-gut fullness and discomfort.
A second study found that despite burning more of the ingested carbohydrate at 120g an hour, there was no extra sparing of the body's own glycogen stores, and oxidation efficiency dropped from 86% at 90g to 76% at 120g. In plain English: a chunk of those extra carbs simply wasn't being used.
The takeaways I give my athletes: carbohydrate during exercise absolutely improves performance, but the benefits beyond about 90g an hour are not consistently supported. More carbs does not automatically mean a faster race. GI tolerance gets harder as intake climbs. High-carb strategies are an individual experiment for experienced athletes with well-trained guts, not a default target because a pro on Instagram does it.
For most trail and ultra runners, 60–90g an hour, well practised, beats 120g an hour badly tolerated. Every time.
Your gut is trainable, the same as your legs. Competitive eaters aren't born with expandable stomachs, they train them. Research backs this up: two weeks of gut training with carbohydrate has been shown to improve GI symptoms, reduce malabsorption and improve running performance compared to placebo. There are three parts to the system you're training: the stomach itself, gastric emptying, and absorption in the intestine.
Here's the gut training protocol I use with my athletes:
Start 6–8 weeks before your race. Earlier if you have the runway. This is not a race-week job.
Begin at a level you know you can tolerate. For most runners that's 30–40g an hour in week one. Progressively increase the grams per hour each week.
Start fuelling early in the run. As early as 15–20 minutes in. This maximises the time you spend practising and mirrors what you'll do on race day. Don't wait until you're hungry, by then you're behind.
Practise in 1–2 sessions per week. Choose the longer and harder sessions, ideally the ones that most closely mimic race conditions and intensity. As a rule, I want my athletes practising carbs on every run over 2 hours.
Use your exact race-day products. Same brands, same flavours, same combination of real food, drinks and gels. This is how you flush out the brand or ingredient that doesn't agree with you, in training, where it costs you nothing.
Keep detailed notes. What you ate, how much, and how you felt: energy, gut comfort, performance, recovery. My athletes log this in TrainingPeaks against every long run. Keep your wrappers so you can audit exactly what went in.
Use B and C races as full dress rehearsals. A lead-up race is the closest thing to race-day conditions you'll get.
Everyone's ceiling is different. Some runners will comfortably build to 90g an hour, others will top out at 65g. That's fine. As long as you're making progress through the gut training cycle, you're improving your race.
Numbers on a page are nice. Here's what a plan actually looks like. These are the kinds of plans I build with athletes for races like UTA50, UTK50, the Guzzler and the Great Ocean Trail Ultra, adjust the products to your own tested favourites.
Say you're running a 50km trail ultra with 2,000m+ of vert and you expect to be out there around 8 hours. At 70g an hour from hour one, you need roughly 500g of carbohydrate across the day. In gels alone that's over 20 gels. Nobody wants that, and by hour five your stomach will agree. So we mix it up:
| Hour | What goes in | Approx carbs |
|---|---|---|
| 1 | 500ml drink mix + a few snakes, starting 15–20 mins in | 65–70g |
| 2 | Pikelet with jam (wrapped in foil) + drink mix | 70g |
| 3 | Enduro sandwich + snakes + water | 70g |
| 4 | CP2: banana + drink mix refill + crushed crisps from the zip lock | 65–70g |
| 5 | Gel flask (concentrated mix) + K-Time twist bar | 70g |
| 6 | CP3: half cup of soft risotto or noodles + lollies | 65–70g |
| 7 | Gel flask + snakes, whatever is still going down easily | 60–70g |
| 8 | Sip drink mix to the finish, small lollies | 40–50g |
A few things to notice. Real food carries the early hours, when your stomach is happiest and solid food is still appealing. Liquids and gels get saved for later, when chewing feels like a second job. Sweet and savoury alternate, crisps and Deb mashed potato gel are worth their weight in gold from hour four, because flavour fatigue is real and by mid-race the last thing you'll want is another sickly-sweet gel. And nothing on this list is exotic: pikelets, snakes, crisps, a vegemite sandwich. The supermarket is full of race food.
Same principles, different emphasis. At 100k pace you're moving at a lower intensity, so the hourly target drops, but the plan has to survive 15+ hours, night running, cold, and the inevitable rough patch. Total intake for the day lands somewhere around 850–950g of carbohydrate.
The differences from the 50k plan:
More real food, and more savoury. Sweet fatigue that's annoying at hour five is plan-ending at hour eleven. Soup with noodles, 2 minute noodles sent to a checkpoint in a Thermos, half a cup of simple risotto or pasta, banana bread, gingernut biscuits. Substantial food also gives your crew something meaningful to prepare.
Use your drop bags and crew deliberately. Hot food at major checkpoints is planned in advance, not improvised. A Thermos of noodles at the 60km checkpoint has saved more than one of my athletes' races.
Expect appetite to disappear, and fuel anyway. Early and often, never letting the stomach sit empty. Small amounts every 20–30 minutes beats a big feed every 90.
Plan for the night. Everything gets harder in the dark: appetite, motivation, fine motor skills. Pre-open packets, use foods that work cold, and put your easiest-to-eat options in the night sections of the plan.
Have a Plan A, B and C. Plan A is your rehearsed intake. Plan B is your backup products when A stops appealing. Plan C is the aid station table. Check what the race provides beforehand so Plan C isn't a surprise.
Sports nutrition is expensive, and a 100k on branded gels alone can run you well north of $100. Two of my favourite budget options: mix your own drink with maltodextrin and fructose at roughly 2:1 (about 660g malto to 330g fructose per kilo bag), or buy plain dextrose cheaply from a homebrew shop as a drink-mix substitute. Same carbs, fraction of the price.
Racing in Australia means racing in heat, whether that's a warm autumn UTA, the Guzzler in a mild Brisbane winter that still hits 22 degrees by midday, or UTK in the Snowies where late November can serve up heat and snow in the same weekend.
Heat changes your fuelling in ways worth planning for:
Your gut gets grumpier. Blood gets shunted to the skin for cooling, which means less blood flow to the gut, slower gastric emptying and a higher risk of nausea. The intake that worked in your cool training block may not work at 30 degrees. If your race will be hot, do some of your gut training in the heat of the day, not at 6am.
Separate your carbs from your hydration. This is one of the most useful habits in hot racing. If all your carbs live in your bottles, then on a hot day drinking to thirst means massively overshooting your carb target, or holding back fluids to protect your stomach. Carry carbs as food and gels, and keep at least one bottle as plain water, so you can adjust each independently.
Lean liquid when solids stop working. Drink mix and gel flasks are easier for a heat-stressed gut than a sandwich at 2pm in full sun.
Drop the hourly target before you drop the plan. On a hot day, 50–60g an hour that stays down beats 80g an hour that comes back up. Ease the intake back, keep sipping, and rebuild when the gut settles or the day cools.
Sort your sodium, sensibly. Sweat rates in Australian summer racing can be huge, and electrolytes matter, but the industry has also convinced runners they need far more than they do. I've written a full piece on this: do you really need all those electrolytes?
Carb loading is not a bowl of pasta the night before. Done properly, it's a deliberate 24–48 hour process for any race longer than about 90 minutes.
The targets: 8–12g of carbohydrate per kg of body weight per day in the 1–2 days before the race. For a 70kg runner that's 560–840g of carbs a day, which is a lot of eating, and it's why winging it doesn't work. Plan it out beforehand.
How to make it manageable:
Go refined. White rice, white bread, refined carbs are your friend here. Drop the fibre for the last 48 hours, the brown rice and wholegrains that serve you well in training will not serve you well at kilometre 30.
Sugar over starches when volume gets hard. Sports drinks, juice, lollies. Liquid carbs let you keep loading without feeling like a stuffed toy.
Reduce protein and fat. They're not the priority right now and they take up room.
Expect the scales to jump. Every gram of stored glycogen binds 3–4g of water, so 1–2kg overnight is normal and good. That's not fat, it's fuel and hydration you'll be very glad of at hour six. What goes in must come out, mind you, so factor the morning queue for the loo into your race-morning timeline.
Remember the taper cuts your needs. You're training less in race week, so your baseline calorie requirement is down even while carbs go up. Loading is about carbohydrate, not about eating everything in sight.
Race morning breakfast tops up liver glycogen, which drains overnight even while muscle glycogen stays put. Familiar, practised, low fibre, 2–3 hours out. You've rehearsed this on your B and C races, right?
Aid stations are where well-built plans go to die. Minutes leak away fast when you're tired, and the food table can seduce you into abandoning a rehearsed plan for a random handful of party mix. My rules:
Arrive with a job list. Fill bottles, grab your planned food, restock pockets, go. Know what the station stocks before race day so nothing is a decision.
Beware the chair! Sitting down is how a 3-minute stop becomes a 20-minute stop. If you must sit, give your crew or your watch a hard time limit.
Leave eating. Walk out of the checkpoint eating rather than standing there finishing your food. That's free time.
Never leave with an empty stomach or empty bottles. Early and often applies at checkpoints too.
Restock your pockets for the whole leg. Count the hours to the next station and load carbs accordingly, plus a bit spare. Running out of food 40 minutes before a checkpoint is a rookie error with a simple fix.
There's more on race-day logistics in race day prep: 6 things I wish I knew when I started trail running.
Even well-trained guts have bad days. Bloating, nausea, the moment where the thought of one more gel makes you gag. It happens to almost everyone at some point in an ultra career, and it is nearly always recoverable. The framework I give my athletes:
Accept. Don't panic. It's a moment in time, not the end of your race.
Diagnose. Quick assessment. "I feel nauseous." "I feel bloated and full."
Analyse. When did I last eat or drink? What's my pace and effort been doing? Nine times out of ten the answer is in one of those two questions.
Plan. Usually: back the effort off, sip small amounts of water, and wait 15 minutes before eating again. Then restart gently, small amounts, ideally something different from whatever triggered it. Cola or plain water and crisps have restarted a lot of stomachs.
Take action. Things rarely get worse from here. The runners who panic and stop eating entirely are the ones who bonk an hour later, the problem was never the one bad gel, it's the 60 missing grams every hour afterwards.
The low point will come in any ultra, usually somewhere in the second half, and it's almost always fixable with food, a change of rhythm and 20 minutes of patience.
How many carbs per hour should I eat in an ultramarathon? Most runners race best on 60–90g of carbohydrate per hour for a 50k, and 50–70g an hour sustained for 100k and beyond. Use a mix of glucose and fructose (around 1:0.8) to maximise absorption, and build your personal number through 6–8 weeks of gut training rather than copying someone else's.
Can I just use gels for an ultra? You can, but almost nobody enjoys hour seven of a gel-only strategy. Real food early, gels and liquids late is the pattern that works for most of my athletes. For anything beyond about 2–3 hours, mixing in solid food improves both morale and tolerance.
What should I eat during a 100k ultra? More real food and more savoury options than a 50k: sandwiches, noodles, soup, risotto, crisps, banana bread, alongside drink mix and gels. Plan hot food at major checkpoints via drop bags or crew, and put your easiest-to-eat items in the night sections.
Do I need to carb load before an ultra? Yes, for any race over about 90 minutes. Aim for 8–12g of carbohydrate per kg of body weight in the 1–2 days beforehand, cut fibre for the last 48 hours, and don't be alarmed by 1–2kg of water weight. It's stored fuel, not a problem.
What do I do if I can't stomach food during a race? Slow down, sip water, and wait 15 minutes before trying again with something small and different. Reduced effort restores blood flow to the gut and most stomachs come good. Whatever you do, don't stop fuelling for the rest of the race, that guarantees the bonk you're trying to avoid.
Every runner has a nutrition plan on race day. The only question is whether it's one you built and rehearsed for months, or one improvised at a checkpoint table at hour six. Having reviewed the race data on both, I can tell you which one finishes stronger.
If you want to go deeper, the full race nutrition masterclass covers everything here plus the Q&A from my athletes. If you want your fuelling built into a structured, race-specific build for races like UTA, UTK, the Guzzler or the Great Ocean Trail Ultra, that's exactly what my trail and ultra training plans are for. And if you want it all individualised, gut training scheduled into your actual weeks, plans reviewed against your race data, and a coach to message when the wheels wobble, come have a look at online coaching.
Train the gut like you train the legs. It'll pay you back at hour six.