Fuelling For Your First Ultra

Nutrition and hydration is many runners’ favourite topic  – and for good reason. What one eats and drinks while running is as individual and important as having comfortable running shoes. But getting nutrition and hydration right is generally more difficult than finding the perfect shoe. Firstly, it’s not guaranteed to work the same on every race, and secondly, it tends to become more challenging with longer distances. For events from 5km to the marathon, the long run training distance is often close to the full race distance, meaning one can practise an exact nutrition plan in training and then execute it on race day. One of the problems with ultras is that it’s not practical to simulate your 100 miler in training a few weeks out from the event  –  not even if it means you will nail your nutrition and hydration on race day…


Statistics from post-race surveys consistently point towards gastrointestinal (GIT) distress being the number one cause for athletes dropping out of 100 milers. Interestingly, this applies to both novice and seasoned ultra runners with elite athletes often citing GIT issues as the reason for a poor performance. But if nutrition and hydration is “trainable,” and one assumes that elite athletes are training close to race distance even for ultras, why are they not getting it right consistently? And how can you, as a first-time ultra runner, be expected to get it right? Let’s take a look at what the science says!

Carbohydrates, fats and proteins are the three macro-nutrients from which we derive all our energy for physical, physiological and mental demands. What differs from one activity to another is the composition of the fuel mixture used, which depends on the rate at which the energy is required and macro-nutrient availability. At rest and low-intensity exercise the majority of energy used comes from fat – a great energy source but slower to break down into usable fuel than carbohydrates. Does this mean you don’t need carbohydrates on an ultra with a slow pace or low intensity? Well in theory, yes. We can survive on body fat alone for weeks, not hours. But we don’t run ultras to test survival – we expect to arrive at the finish line alive; we’re more interested in how quickly we can get there. Even the last runner on the course is racing the clock for cut-offs. So include carbohydrates in your ultra nutrition plan to keep you moving quicker than at mere survival pace.

According to the International Society of Sports Nutrition (ISSN), athletes competing in a single-stage ultra marathon should aim to consume 30-50 grams per hour of carbohydrates and 5-10g/hour of protein, through a variety of calorie-dense foods. While protein is essential for muscle repair, immune function and enzyme production, it is not a major source of energy during exercise. Focusing on consuming sufficient carbohydrates should result in adequate protein intake as a “by-product” of what you consume for calories, except in extreme circumstances such as multi-day ultra runs and stage races. Some sources recommend a higher carbohydrate intake of 60 to 90g/ hour. This is based on the fact that the body is able to use approximately 1 gram of exogenous (from an external source) carbohydrate per minute while exercising, and if different types of sugars are consumed in the correct ratios you may be able to engage additional mechanisms to utilize up to 1.4g/min.

So what do all these figures imply when planning nutrition for your first ultra? Simply put, you should aim to consume a minimum of 30-40 grams of carbohydrates per hour. This is a good target for lighter, female athletes that struggle with nutrition (females burn carbohydrates at a slower rate than males.) If you’re an average sized male or female without a history of GIT issues then aim for 50-60g/hour. If you’re taller than average or looking to run at a more competitive pace then a target of above 60g/hour would be preferable. These estimations are based on an equation called the caloric burn rate which states that you burn one calorie per kilogram per kilometre of flat running.

It is therefore safe to assume that the more ascent in your race and the more you weigh, the more calories you will require. If you are aiming for the top-end 90g/hour of carbohydrates then it is advisable to do additional research on glucose and fructose absorption, or work with a coach who has a particular interest in nutrition. Ingesting more carbs than your digestive system can process is a common cause for gastric distress. The excess carbs remain in the gut, which has an already compromised blood supply during running, and intestinal bacteria acting on the carbohydrates cause gas release which leads to bloating and nausea.


In addition to satisfying energy demands while running, it is necessary to take in sufficient fluids. Hydration is even more important than nutrition because while low energy can be corrected within 30 minutes by consuming calories, a poor hydration status takes hours to correct. Also, body fluid plays a multitude of essential roles for the ultra athlete such as:

  • It is largely responsible for core temperature regulation by sweating – the body’s primary cooling mechanism through evaporation.
  • It affects gut motility and digestion. In order for gastric emptying to occur (movement from stomach to intestine) the concentration of the stomach contents needs to be correct. This is the reason that gels require a certain amount of water to be consumed simultaneously. In the intestine, water is again required for optimal osmolality to ensure nutrient uptake into the blood.
  • Water is critical in maintaining blood volume. Approximately 5 litres of blood constantly circulates through your body, performing tasks such as carrying heat away from your core, delivering oxygen to muscles and nutrients to cells, and donating fluid for sweating. Inadequate hydration results in reduced blood volume and these functions become compromised.  This places athletes at increased risk of hypothermia in cold, wet mountain ultras and heatstroke during extremely hot events.
  • Removal of metabolic waste products is another important function of body fluids. Ultra runners in particular experience a significant amount of muscle damage over the course of 100 kilometre and 100 mile events. The by-products of muscle breakdown are filtered from the blood by the kidneys, but dehydration impairs this process and can lead to permanent kidney damage.

Right, that’s informative. But how much fluid do you actually need to consume on an ultra?  According to the ISSN fluid volumes of 450 to 750ml/hour are advised, but this does not take into account body weight, intensity or environmental conditions. I recommend a minimum of 500ml/hour in cool conditions. As with caloric requirements, fluid requirements increase proportionately to body weight. To obtain a more accurate and individualised estimate, perform a simple sweat test and repeat it several times under similar conditions to determine your own average sweat rate per hour. In an ultra dehydration adds up significantly over many hours, making fluid replacement more important than during marathon races.

There is no fixed percentage of your sweat loss that you should aim to replace (do not try to replace 100% of fluid lost – this is dangerous and can lead to over-hydration and hyponatraemia.) Rather, you want to avoid becoming more than 2% dehydrated in the early part of the run and aim to finish no more than 4% dehydrated. If you’re unable to eat, feel nauseous or aren’t thinking clearly then you may be excessively dehydrated. Use the value obtained from your sweat testing to place your fluid needs somewhere along a scale of 500 to 1000ml per hour. Then experiment to find your optimal fluid intake in different conditions.


The third and final element of ultra hydration and nutrition is proper electrolyte replacement. Sweat rate is only one component of sweat testing, the other being sweat sodium concentration. This is the amount of sodium (a constituent of salt) which you lose per litre of sweat and another highly individualised value. Sweat sodium concentration is more tricky to test for and usually requires a sports laboratory or medical facility, but fortunately sodium intake guidelines for athletes are relatively consistent across sources. The ISSN recommends a sodium intake of more than 575mg per litre of fluid consumed. There are two important points to make here. One, unlike fluid and caloric intakes which are based on per hour of running, sodium must be consumed relative to fluid, hence the per litre of fluid consumed measurement. Secondly, the ISSN notes that a value of 575mg/L is above that provided by most commercial products, so pay special attention to the sodium content of your electrolyte sport drinks.

Depending on whether or not you’re a particularly “salty” sweater, it would be reasonably safe to aim for a sodium intake of 600-800mg per litre of fluid. Assuming you’re using an electrolyte product (drink mix, electrolyte tablets or sodium tablets) as well as eating solid foods like bars and taking gels, you’ll need to add up the sodium content of everything you consume during your long run. Divide this by the total volume of fluid ingested on the run to find your sodium intake as a milligrams per litre (mg/L) value.

This may seem like a lot of information to digest (excuse the pun) but it might also give you a better idea of why even seasoned ultra runners still struggle with hydration and nutrition. Unfortunately, there is no better way to figure out what works for you personally than through trial and error. That said, use the ball park figures given above along with what you already know in terms of your own weight, sweat rate and expected conditions on the ultra for which you’re preparing. Develop a nutrition and hydration schedule, or work with a coach or sports nutritionist to design one, and test it as much as possible in training. Rule out what doesn’t work for you and include that which does work in future sessions. Then arrive at race day with your nutrition plan in mind and follow it as closely as possible, without being too unadaptable. After the event, and every long training run in fact, log your fluid, calorie and sodium intakes in a diary along with how you felt and any notable dietary “yays or nays.”

If you are still running ultras in ten years time (and many a once-off ultra runner is, I assure you!) you’ll be grateful for a detailed nutritional record somewhere down the line. I ran my first ultra in 2014 and I’ve run many since, but I’ve never kept an ultra diary. The result? I can count on one hand the ultras on which I nailed my nutrition, but I have only a vague idea of what I did right on those days. And so, like a first-time ultra runner, my quest for the perfect ultra running nutrition continues…

About the author: Nicolette Griffioen is a South African mountain, trail and ultra coach and athlete. She is trail ambassador for inov-8 South Africa and is living her best life as a Drakensberg nomad.

"But getting nutrition and hydration right is generally more difficult than finding the perfect shoe. Firstly, it’s not guaranteed to work the same on every race, and secondly, it tends to become more challenging with longer distances."

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Global - Virtual


A virtual race which can be run at any time shown on the dates shown, on any type of terrain in any country.

Suitable for

For runners from beginners to experienced as you choose your own course and challenge based on the guidelines and options set by the virtual race organiser.

Endurance - Multi-activity


An ultra distance race including at least two of the following activities such as running, swimming, cycling, kayaking, skiing and climbing. It may also include different climatic conditions (eg ice, snow, humidity, cold water, mud or heat).

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Experienced multi-skilled athletes who have trained for the different activities included in this event. Admission to these races may be subject to receipt of a recent medical examination certificate. Check with the race organiser regarding entry requirements and any specialist equipment required such as a wetsuit, skis or a mountain bike.



Increase of up to 2000 metres with very challenging climatic conditions (e.g. ice, snow, humidity, heat or at high altitude)

Suitable for

Very experienced long distance ultra runners (min 3 years’ experience) or are doing regular long distance running (>50 miles) with elevation and conditions shown (where possible). Admission to these races is often subject to receipt of a recent medical examination certificate. Purchase of specialist kit is often recommended for these races.



Increase of up to 2000 metres with some challenging climatic conditions (e.g. ice, snow, humidity or heat)

Suitable for

Experienced runners who have completed at least 4 ultras in last 12 months, or are doing regular long distance running (>50 miles) with elevation and conditions shown (where possible). Admission to these races may be subject to receipt of a recent medical examination certificate. Check with the race organiser regarding entry requirements.



Increase of up to 1500 metres

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Runners who have completed several ultra distances or similar events, or are doing long distance running regularly, with elevation shown.



Increase of up to 1000 metres

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Runners who have completed at least one ultra in last 6 months or are doing long distance running (>26 miles) regularly, with elevation shown.



Very little change < 500 metres

Suitable for

First ultra event. Runners completing a marathon or doing regular long distance running (>26 miles) in the last 6 months.