How to lose fat ultra running

Last updated: 22-Aug-18

By James Eacott

I should start by stating that I’m not a nutritionist. My advice comes from eight years of ultra running and three years in triathlon, and time coaching both sports. So although this knowledge doesn’t come from a text book or degree, I’ve tried and tested most methods on myself and my athletes. So, I thought I’d share the things that I’ve seen work.

I wanted to write this article because many ultra runners start out in the sport expecting to become super-lean. However, they soon find that that’s not the case, for many reasons. I won’t go into the reasons as to why that happens – there are loads – and instead dive straight into what you can do about it: how to incorporate fat burning tactics into your ultra running training regime.


First off, it’s important to highlight the difference between fat loss and weight loss. It’ll be obvious to most of you but those new to sport and fitness often use the terms as if they’re the same thing. They’re not:

  • Weight loss is the aim of reducing your overall mass (i.e. the number on the weighing scales).
  • Fat loss is the aim of specifically targeting a reduction in fat mass.

A reduction in overall body mass is an important first step if your overall health is in jeopardy. There are many different ways to reduce your weight and not all strategies work for everyone. Find what works for you.

As athletes, we’re more interested in body composition – what our mass is made up of – and how to alter this to improve performance. Whether you’re 60kg or 90kg is slightly irrelevant: what matters is what that mass is made up of and how much is dead-weight that you’re lugging around.

It’s also worth pointing out that the amount of fat required for optimum performance varies depending on what ultra distance you race. For example, the best 50km runners are physiologically similar to elite marathon runners: super lean with very little fat. On the other hand, multi-day specialists often carry more bulk both in muscle and fat. This article comes from the premise that applies to most of us: that we could do with losing a little fat to improve performance.

There are two methods to shift fat: Training and Nutrition.


1. HIIT – High Intensity Interval Training
On the whole, ultra runners ignore HIIT training. We don’t like it. It hurts. It’s what young whippers do to prepare for a 5km. Our long slogs have nothing to do with silly speed stuff. So often I hear “I race long distances at a relatively slow place so why do I need to sprint?”. Yes, long training runs are obviously crucial for ultra runners but HIIT training is necessary not only for fat burning, but it’ll also improve your endurance speed.

Here’s why: A long, low intensity run is great for building strength, a solid aerobic base and the mental strength required for ultras. All good. And, while you’re running (that bit is key) it’s good for tapping into fat stores. However, once you stop and put your feet up, your body returns to stasis quite rapidly.

HIIT training has the opposite effect: it’s done at such a high intensity that the sessions are relatively short and you may not burn a huge number of calories during the session itself. But the after-burn effect – your EPOC (post-exercise oxygen consumption) – is increased massively and you can be torching calories for up to 36 hours after you’ve finished. That’s serious bang for your buck.

How to do it
There are 2 types of interval training relevant to ultra runners:

1. True Speed  
 Warm up Jog easy for 10 minutes and throw in 5 x 20s strides.
 Main set 15 second all-out sprint then walk for 60s. Complete 10 – 20 reps.
 Work:rest ratio around 1:4. Aim for 10 – 20 reps.
 Over time increase the work period so future sets could be: 30s on / 2 min off
  45s on / 3 min off
  60s on / 4 min off

To justify the long rest, you really need to leave it all out there and go for it.

2. Speed – Endurance Only marginally lower intensity than True Speed pace (around 5km pace).
 Warm up 10 min easy jog with strides.
 Main Set 1:30 hard then 3 minutes off. Complete 10 – 15 reps.
 Work:rest ratio 1:2
 Progress up to ‘on’ periods of 4 minutes, such as: 2 min on / 4 min off
  3 min on / 6 min off

Again, to earn the rest you need to be really switched on.

If you’re new to running and are not comfortable sprinting, then it’s still great to do fat burning sessions on a rowing machine, bike or other gym equipment. See our article on cross training for ultra-runners.

2. Fasted runs
Unlike HIIT sessions, for which you must be adequately fuelled, fasted runs are those where you run in an energy deficit.

Carbohydrates are your body’s predominant fuel source. For as long as carbs (glucose, essentially) are available in your muscles and liver, that’s what you’ll use for energy. Our bodies can only store so much, though, so if you limit carb intake before a session your body will turn to its second go-to source: fat.

How to do it
Once a week, run in the morning on an empty stomach. Have an early dinner the night before and you’ll have essentially fasted for 12 hours. When you run, you must keep it low intensity – conversational pace – in order to tap into those fuel stores.

Afterwards, eat a good breakfast with plenty of protein and a few carbs. Job done.

Adding one HIIT session and one fasted run into your schedule per week will reap carnage on that tyre around your middle!


You cannot out-train a poor diet. My experience has shown that nutrition is more important than exercise when it comes to body composition. I’d say nutrition is 60% responsible for body composition. You can change your composition and lose fat even if you do very little exercise, as long as you eat the right things at the right time. On the other hand, even if you train like a beast but eat rubbish, you won’t shift fat.

1. Periodise carbohydrate
Carbs have wrongly become the enemy in many athlete’s eyes. Periodisation of carbohydrates around your sleep and training schedules is crucial to losing fat. What this means is: eat carbs at the right time.

Unless you’re in your build or peak training phases, you do not need the stack of carbs that modern man has become accustomed to consuming. Cutting carbs out of your evening meal is a great place to start. I tend to stick to meat and veg / salad unless I’ve had a particularly hard day (training 2+ hours).

The same goes for some training sessions. You do not need to load up for all of them. Yes, for sprint sessions you need to be fuelled with some quick-release sugars: a bagel with jam is perfect.

On your average training day, consume most of your carbs at breakfast, have a few at lunch and then none at dinner. When you have a big session coming up, aim to eat 30g before and another 15g along with 30g protein.

2. Decrease sugar and increase protein
Sugar is, in my opinion, the real enemy. It’s a topic that’s been covered in depth over the last decade and we need to listen to the science. I’m not a dietician, but it makes perfect sense to me that if sugar is consumed and not burned off, then that sugar will turn into fat.

The best way to reduce your sugar intake is to start a food diary. Use an app like MyFitnessPal to track your food for a week. Record everything – food and drink – and you’ll be surprised how much sugar you consume. I thought I ate healthily, but I was surprised to find a few items much higher than expected.

Protein is a key macronutrient in the process of fat loss. When someone tries to lose weight (not specifically fat) they tend to lose both fat and muscle. This is because they restrict calorie intake and do lots of long, slow cardio sessions. This may burn some fat but it’ll also wreck muscle. Muscle is heavier than fat so the reduced number of the scales may purely be as a result of muscle loss.

By increasing your protein intake while on a more carb-restricted fat loss diet, you ensure that not only do you target fat but also that your muscle definition remains.

One final point about making sure you’re consuming enough protein (at least 1.5-2g per kg bodyweight per day) is that it’s very filling so you’re less likely to overeat.

Stay sensible, think longer term and good luck!

If you would like to download a pdf version of this or other Run Ultra training guides, visit our Member’s area



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Date Range

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).

Suitable for

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

Suitable for

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

Suitable for

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.