Ultra Marathon Fuelling Guide

Ultra-running asks something different of the body than a marathon does. Where a marathon is a hard, glycogen-fuelled push lasting a few hours, an ultra is a multi-hour (sometimes multi-day) negotiation between energy in and energy out, run on tired legs, a reluctant gut, and - just as much - a tiring mind. The athletes who finish strong tend to treat fuelling less like a single race-day decision and more like a skill they've trained - as adaptable and well-rehearsed as their legs.

Table of Contents

• Why Ultra-Marathon Fuelling Is Different

• Train Your Gut: Eat Early, Eat Often

• Carbohydrate Strategy: How Much, And What Kind

• Protein & Fat: The Macronutrients Everyone Forgets

• Electrolytes & Avoiding Hyponatremia

• Mental Energy Matters: Fuelling the Brain, Not Just The Legs

• Caffeine: Using It Strategically

• Putting It Together: A Sample Race-Day Fuelling Plan

• Take Home Points

Why Ultra-Marathon Fuelling Is Different

Marathon fuelling advice - a gel every 20 minutes, water at every aid station - breaks down once you're out on course for six, twelve, or twenty-four hours. Three things change: total calories needed go up, and gels alone can't cover it without wrecking your stomach ¹,²; lower intensity means the body leans more on fat, so metabolic flexibility matters ²; and the gut itself becomes the limiter, with GI discomfort a leading reason athletes slow down or drop out ¹,³.

An ultra rewards a body that can adapt on the move. Your nutrition plan needs to flex too - different foods, different intake rates, and more tolerance for savoury, dense, "real" food as the race wears on ¹.

Train Your Gut: Eat Early, Eat Often

The gut is trainable. Repeated exposure to carbohydrate and mixed foods on long runs improves absorption and reduces bloating, cramping, and nausea this is “gut training,” and it should start months out, not the week before ¹,³. Train on the same foods, in the same order, you plan to eat on race day, building volume gradually rather than trying something new mid-race ³. Whole foods belong in the mix alongside gels, especially as races extend past marathon distance and appetite for sweet, gel-like products drops off ¹.

A few reliable options to train with:

• Pikelets with nut butter

• Hot cross buns, pretzels or fruit

• Cheese and Vegemite sandwiches or 2 minute noodles

• Radix Nutrition Ultra Meals or Styrkr BAR+ Protein Rice Bars

Carbohydrate Strategy: How Much, and What Kind

Carbohydrate remains the main fuel above an easy pace, but the right target for an ultra differs from marathon advice. Aim for 30–50 g per hour as a realistic baseline, increasing toward 90 g per hour only if you’ve specifically trained your gut for it ¹,³. Finishers of 100-mile races average closer to 44 g per hour - well below marathon-style targets, simply because it’s harder to sustain high intake many hours into a race ¹.

Mixing glucose and fructose (“multiple transportable carbohydrates”) lets your gut absorb more per hour without a proportional rise in GI distress. That’s why most gels and drink mixes list both on the label ²,³.

In day-to-day training, aim for 5–8 g/kg/day of carbohydrate to avoid chronic glycogen depletion, even if you plan to race using a more fat-reliant strategy ¹.

Protein and Fat: The Macronutrients Everyone Forgets

Protein → Aim for 5–10 g per hour during racing. Finishers of ultra races consume roughly twice as much protein per hour as non-finishers ¹. It may help offset central fatigue (see Section 6) and support muscle repair. Day to day, spreading protein as roughly 20 g every three waking hours supports muscle repair better than eating the same total in one or two large meals ¹,⁴.

Fat →Reliance on fat rises as races lengthen, and appetite often shifts toward savoury, fattier foods- cheese, salami, nut butters- which also provide useful sodium ¹. Some athletes train “fat-adapted” (higher fat, lower carb) to spare glycogen. Keto-adapted ultra-runners show higher fat-oxidation rates, but evidence that this translates to faster race times is still limited ¹,⁵. For most runners, adding whole foods rich in fat and protein later in a race -without going fully low-carb - is the safer, better-supported approach ¹,².

Electrolytes & Avoiding Hyponatremia

Sweat losses over many hours can be substantial, and they include more than water: sodium, potassium, and magnesium are lost too. Under-replacing electrolytes is linked to cramping and nausea, but sweat sodium concentration varies several-fold between people, so a “one size fits all” dose rarely works ¹,⁶. Test your own sweat losses during training, practise your race-day drinks and electrolytes beforehand, and use a general-purpose product like Skratch Labs Sport Hydration Mix or Näak Ultra Energy Drink Mix Sachet as a starting point if you haven’t dialled in your own numbers. A useful target is 500–700 mg sodium per litre of fluid, with total intake around 450–750 mL per hour, adjusted for heat, body size, and gut tolerance ¹,⁶.

The bigger risk is exercise-associated hyponatremia (EAH) -a drop in blood sodium, usually caused by overdrinking rather than under-salting ⁶. The strongest prevention is simple: drink to thirst, not by the clock, and don’t assume more fluid is always safer ⁶. EAH symptoms (headache, nausea, confusion) can mimic dehydration, which is exactly the danger. If in doubt, get medical help rather than drinking more ⁶.

Mental Energy Matters: Fuelling the Brain, Not Just The Legs

Ultras challenge the mind as much as the body. Steady blood glucose, good hydration, and specific brain-supporting nutrients may all help reduce the “mental fog” that can set in late in a race ¹,².

One proposed explanation is the central fatigue hypothesis: during prolonged exercise, a rise in tryptophan relative to BCAAs may increase brain serotonin, which is associated with perceived fatigue. Protein or BCAAs during exercise may help address this, alongside steady blood glucose. This may be one reason some gels, bars, and drink mixes include added BCAAs ¹,⁷.

Ketone esters are sometimes discussed in this context because the brain can use ketones as fuel when glucose is low. They’re worth knowing about, but not building a race plan around: the ISSN position stand says there isn’t enough evidence yet that ketone esters improve ultra-marathon performance ¹.

Options worth trying → 226ERS High Energy Gel- Blackcurrant (contains BCAAs), deltaG (ketone ester), and Radix Nutrition Ultra Meals.

Caffeine: Using It Strategically

Caffeine is one of the better-supported performance aids in endurance sport, with strong meta-analytic evidence behind it ⁸. In ultras, it may be especially useful later in the race, when sleep deprivation during overnight events can affect alertness and decision-making ¹.

Rather than front-loading it early, hold some caffeine in reserve - gels, chews, or aid-station coffee - for when you need it most, and test your dose in training first.

Putting It Together: A Sample Race-Day Fuelling Plan

Every athlete’s needs vary with body size, pace, conditions, and gut tolerance. Use this as a starting template to adapt and test during training, rather than as a fixed prescription ¹:

• Hourly energy: roughly 200–400 kcal/hour for events beyond 100 km, and 150–300 kcal/hour for shorter ultras (around 50 miles) ¹
• Carbohydrate: 30–50 g/hour, increasing toward 60–90 g/hour later in training only after your gut is trained to tolerate it ¹,³
• Protein: 5–10 g/hour, particularly from the middle of the race onward
• Fluid: roughly 450–750 mL/hour, adjusted to thirst and conditions—not a fixed target ¹,⁶
• Sodium: 500–700 mg/L in fluids during hot or prolonged efforts, plus salty whole foods as your appetite shifts ¹,⁶
• Food mix: sweet options early (gels, dates, bananas, sports drink); savoury, fattier, more calorie-dense whole foods from the midpoint onward ¹
• Caffeine: held in reserve for the back half of the race or overnight sections ¹,⁸

Take-home Points

Ultra-marathon fuelling is a trained skill, not a race-day improvisation.

• Start gut training months out, not weeks

• Aim for 30-90g/hour of carbohydrate: 30-50g/hour as a baseline, up to 90g/hour only if you've specifically trained your gut for it

• Don't neglect protein and fat as the race lengthens

• Be deliberate about sodium, but let thirst set your drinking pace, not the clock - overdrinking is the bigger danger, not running low on salt

• Support the brain as well as the legs - BCAAs and, more speculatively, ketone esters - and keep caffeine in your back pocket for when you need it most

References

1. Tiller NB, Roberts JD, Beasley L, et al. International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing. J Int Soc Sports Nutr. 2019;16:50.

2. Nikolaidis PT, Veniamakis E, Rosemann T, Knechtle B. Nutrition in ultra-endurance: state of the art. Nutrients. 2018;10(12):1995.

3. Jeukendrup AE. Training the gut for athletes. Sports Sci Exch. 2017;28(178):1-6.

4. Areta JL, Burke LM, Ross ML, et al. Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis. J Physiol. 2013;591(9):2319-2331.

5. Volek JS, Freidenreich DJ, Saenz C, et al. Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism. 2016;65(3):100-110.

6. Bennett BL, Hew-Butler T, Rosner MH, Myers T, Lipman GS. Wilderness Medical Society clinical practice guidelines for the management of exercise-associated hyponatremia: 2019 update. Wilderness Environ Med. 2020;31(1):50-62.

7. Watson P. Nutrition, the brain and prolonged exercise. Eur J Sport Sci. 2008;8(2):87-96.

8. Grgic J, Grgic I, Pickering C, Schoenfeld BJ, Bishop DJ, Pedisic Z. Wake up and smell the coffee: caffeine supplementation and exercise performance - an umbrella review of 21 published meta-analyses. Br J Sports Med. 2020;54(11):681-688.

Disclaimer:
The content in this blog is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment. Always speak with your doctor or allied health team before changing your diet, exercise, or taking supplements, especially if you have a health condition or take medication. Please use this information as a guide only. Aid Station doesn't take responsibility for individual outcomes.