Ultramarathon Nutrition: 60–90 g Carbs per Hour

Up to the marathon, your legs decide how the race goes. Beyond it, your stomach does. Anyone on their feet for six, eight or twelve hours can no longer cover the required energy from glycogen stores — at race pace they last two to three hours depending on speed and training status. Everything after that comes from what you eat and drink on the move. That is why ultramarathon fuelling is not a side detail but the factor that decides between a finish and a DNF.

What changes after hour four

The first hours forgive almost everything. The gut is well perfused, digestion runs smoothly, gels and bars go down the way they did in training. From roughly three to four hours of continuous exercise the picture shifts. At moderate to high intensity, up to 80 percent of cardiac output goes to the working muscles — the gut receives less blood, the intestinal wall is less well perfused, and gastric emptying slows measurably.

At the same time core temperature rises, fluid loss shifts the electrolyte balance, and many runners develop an aversion to anything sweet. That is not a sign of weakness and not an individual intolerance: it is a physiological response to prolonged exercise that affects everyone. The difference lies in whether you have a plan B in your pockets — and whether your gut has learned to work under load beforehand.

There is a second effect that is often underestimated: as duration increases, the willingness to eat at all declines. Appetite disappears, chewing becomes a chore, and anyone who has lived on sweet gels until then eventually gags on the next cube. Ultra fuelling is therefore also a craft of variety.

The numbers: carbs, fluid, sodium

In practice three quantities have proven useful as anchors for your plan. They are a starting point, not dogma — individual tolerance has the final say.

• Carbohydrates: 60 to 90 grams per hour. This rate has established itself in studies and in practice as the upper limit for most runners. Highly trained guts using multiple transportable sugars manage up to 120 grams per hour — but only if intake was built over months. Do not start at 90 grams on race day.
• Fluid: 400 to 800 millilitres per hour. The range is deliberately wide because it depends on temperature, sweat rate and body size. A 60 kilogram runner in autumn needs clearly less than an 85 kilogram runner in midsummer. Drinking more is not automatically better — more on that below.
• Sodium: 300 to 600 milligrams per hour. Lean towards the upper end with heavy sweating, heat, or salty white stains on your clothing. Sodium is the electrolyte actually lost in meaningful amounts during long efforts; potassium and magnesium are secondary during the race because normal nutrition covers them.

Distribution matters more than the total. A rhythm of one small portion every 20 to 30 minutes is far more tolerable for the gut than a big "top-up" at every second station. The stomach processes continuous small amounts better than rare large ones — and that is exactly the difference between a predictable race and a stomach that goes on strike at mile 40.

Why gels fail after hour four

A gel delivers 20 to 25 grams of carbohydrate in concentrated form — efficient in a marathon, problematic in an ultra. Highly concentrated sugar solutions draw water into the gut, which slows emptying further. Combined with reduced intestinal blood flow, this leads to fullness, nausea and in the worse case diarrhoea.

Then there is taste: after five hours the sweetness threshold has shifted so much that a normal gel cube can become unbearable. Runners who say at the finish that they "couldn't get anything down after mile 45" usually do not have a stomach defect — they held on to a single product format for too long.

The solution is unspectacular: mix sweet with salty, liquid with solid, concentrated with diluted. A salty piece of potato or half a cheese sandwich at a station often works better than the next energy shot from a tube — not because it has more calories, but because it gives digestion work in small portions. The fundamentals of race nutrition over shorter distances are covered in fuelling for the marathon.

Gut training: the underestimated block

The gut is trainable — one of the most practically relevant findings in sports nutrition research of the past 15 years. Anyone who drinks only water and eats nothing for months will not tolerate 90 grams of carbs per hour on race day. Those who eat regularly during long runs develop a higher gastric emptying rate, better nutrient absorption in the small intestine and a markedly lower tendency towards nausea and cramps.

The build follows the same principle as training itself: slow, progressive, with enough time. A proven framework is eight to twelve weeks before the goal race.

• Weeks 1–2: 30 to 40 grams of carbs per hour on long runs. Familiar products, no experiments. The goal is habit, not volume.
• Weeks 3–4: Increase by about 10 grams per week. Check whether you can hold the amount for two hours straight without feeling full.
• Weeks 5–8: Deliberately test the products your target event might serve: salty snacks, broth, cola, rice balls. This is the time for intolerances to show up.
• Weeks 9–12: Race-pace simulation. One long run with exactly the fuelling plan you will use in the race — including the timing. If something does not work, there is still time to change it.

A practical note: train the logistics too. Refilling flasks, getting gels out of the back pocket, eating while walking, not stopping at a station. Fuelling that works technically but costs three minutes per station adds up to forty-five minutes across 15 stations. Details on gear and race flow are in ultramarathon training.

Fluid: the most common wrong decision

With drinking, the logic flips compared to eating: too little is a problem, but so is too much. Anyone drinking clearly more than they sweat dilutes the blood and lowers the sodium level — hyponatraemia, which presents with nausea, headache, confusion and in extreme cases loss of consciousness. In ultras it is the most common medical complication of all, and it almost exclusively hits runners who drink heavily "to be safe".

The most reliable way to determine your sweat rate: weigh yourself naked before and after a long run, note how much you drank and work out the difference. One kilogram of weight loss equals roughly one litre of fluid loss. For a four-hour run with 1.5 litres consumed and two kilos lighter at the end, your sweat rate is around 0.9 litres per hour. Numbers like that are more useful than any rule of thumb.

In practice: drinking to thirst is surprisingly reliable for most runners in an ultra, as long as heat and high sodium loss are not in play. In heat and with salty sweat, an electrolyte drink belongs in the plan, not just water. How to mix your own is in homemade sports drink; the basics on sodium, potassium and magnesium are in electrolytes for running.

Sample plan for a 50 kilometre race

The following plan assumes a target pace around 6:00 min/km, so roughly five hours of running, in moderate temperatures. It shows the structure, not the truth for you — your amounts follow from sweat rate and gut tolerance.

• Before the start (2–3 hours out): 80 to 120 grams of carbs as a familiar breakfast, 400 to 500 millilitres of fluid, no fat or fibre experiment.
• Start to hour 2: 60 grams of carbs per hour, split into three small portions every 20 minutes. Plus 500 millilitres of fluid per hour. Gels and bars work fine in this phase.
• Hour 2 to 3.5: Continue at 60 to 75 grams, but now mixed: one gel, one salty snack, half a bar. The stomach only notices the difference between concentrate and solid food later — so mix early.
• Hour 3.5 to 5: Switch to mostly solid, salty food at the stations: potatoes, rice balls, broth, soup. Sweet only as a supplement. Fluid continues at 400 to 600 millilitres per hour, part of it as cola if the stomach feels tired.
• Final 5 kilometres: Nothing new. What has worked so far will work to the finish. No "final push gel" experiments.

That adds up to roughly 280 to 320 grams of carbohydrate across the whole race — plus breakfast. More than most runners expect, and clearly less than pure arithmetic would suggest: the body still covers a substantial share of demand from fat even at high carbohydrate intake.

What actually happens at the aid station

The famous truth about ultras: at some point nothing tastes good and the body rejects anything that looks like sports nutrition. That is exactly where the race is decided. Experienced runners keep three rules ready for it.

• Eat before hunger arrives. Appetite disappears long before energy does. Waiting for hunger means eating too late — and then often too much at once.
• Always carry something salty. A salty cracker, a cup of broth, a handful of crisps: they break the sweet fatigue and deliver sodium with it.
• Do not load the stomach with a big meal. A portion eaten in two minutes often takes an hour before it stops feeling like something. Small amounts while walking are the key.

If the stomach still rebels, a proven approach helps: ease off the pace, switch to liquid calories for 15 to 20 minutes and only sip in small amounts during that phase. Once nausea fades, slowly restart solid food. Anyone who keeps pushing in that situation usually loses more time than someone who deliberately invests a quarter of an hour.

Common ultramarathon fuelling mistakes

• Starting too late. Eating only when hunger arrives means you lost two hours already. The first portion belongs in the first 30 to 45 minutes.
• Sweet only. Gels and sweet bars are efficient in a marathon, unbearable after four hours in an ultra. Salty food belongs in the plan from the start, not as an emergency measure.
• Experimenting on race day. New products, untested station food, a different drink brand — these are the classics behind DNFs. Everything gets tested beforehand.
• Too much at once. A large bar on an empty stomach at mile 30 often does not land where it should. Small portions, continuously.
• Drinking without sodium. For five hours and more with heavy sweat, water alone is not enough. An electrolyte drink or salty food covers the loss.
• Forgetting your teeth. Hours of sugar and acid are a real strain on enamel. Rinse after the race, wait 30 minutes, then brush.

How Peakora links fuelling to your training plan

The Peakora engine plans your long runs not only by distance and pace but also by fuelling task. In the build phase the plan carries long sessions with an explicit note on carbs per hour — progressively increasing, matched to race distance. For a 50 kilometre goal, the last big test run is scheduled so that two weeks remain for corrections.

Because load runs in parallel via TSS and form via TSB, you can also see whether your fuelling sits in proportion to training load: a digestion problem in a high-load week is a different signal than the same problem in a deload week. The basics of load management are in TSS explained, and the final weeks of preparation in the tapering guide.

Frequently asked questions about ultramarathon nutrition

How many carbs per hour do I need in an ultramarathon?

60 to 90 grams per hour, counted from the second hour. Well-trained guts tolerate up to 120 grams if the intake was built over months. Steady delivery without long gaps matters more than the peak number.

Why can't I stomach gels anymore in an ultramarathon?

Because the stomach reacts differently after four to six hours of continuous exercise: blood flow to the gut drops and sweet flavours start causing nausea. Salty, fatty and solid foods usually work better — provided you tested them in training.

How do I train my gut for long runs?

By eating on every long run beyond three hours, using the same products as on race day. Increase by about 10 grams of carbs per hour each week, starting at 30 to 40 grams. The gut adapts over eight to twelve weeks.

How much should I drink during an ultramarathon?

400 to 800 millilitres per hour, depending on temperature, sweat rate and body size. More is not better: drinking beyond thirst risks hyponatraemia. Measure your sweat rate by weighing yourself before and after a long run.

What should I eat at aid stations?

What you tested at home — potatoes, rice balls, broth, soup, cola or salty crackers. Take small portions and eat while walking. Untested products at a station are the most common cause of stomach trouble in the second half.