A big fat lie? Or the secret to ultramarathon success? 

If there’s one subject that can divide a room of ultra runners, it’s the sometimes controversial and ever-polarising subject of diet. Hence I need to insert this caveat into the article before you read on:

I am not a dietitian, nutritionist or doctor. I’m simply a runner who likes to experiment. Below is my experience and it isn’t a recommendation either way to try the dietary intervention spoken about herein. 

Phew, now that’s out of the way…

Social influence 

With the constant infiltration of social media into our daily lives, we’re bombarded by images of influencers touting the latest diet craze that promises results in a matter of weeks…. although some before and after pictures don’t always look like the same person somehow. Strange that. 

So are we, the sensible ultra-runners, immune to these images of ripped athletes in shorter than short shorts? Surely we’re too smart for all of that, right? 

Well, I think we too can fall into the trap of thinking that a dietary switch could be the difference between finishing mid-pack and landing on the podium for our next ultra. Especially with the rise of elite ultra-runners who are themselves polarised in their dietary approach. Some of them choose to evangelise their choices all over social media and even write books about it. Others just quietly get on with it, only speaking about it if questioned by nosey people like me!

Whether we acknowledge it or not, we do pay attention to what our running idols do, say and eat at times. For example, how many of us decided to try a vegan diet after reading Scott Jurek’s book “Eat and Run”? Or even made excuses for eating way too much pizza after reading Dean Karnazes' now iconic book “Ultramarathon Man”?

Which diet is best?

Ultimately I think we’re all the same in our thinking on this aren’t we? We all want to know which is the best one. Which diet is the best for running all day… and possibly night?

As ultra runners, we are known for being curious, obsessed and a bit weird at times. So it’s no surprise that if you ask the internet what the best diet for ultra-running is, you get literally thousands of results. There are forums, blogs, websites, books and YouTube channels dedicated to each way of eating. Many of which opt for the traditional approach to running nutrition. Moderately high carb with lots of pasta, whole grains and vegetables thrown in to keep the energy levels up. It’s mostly simple and seems to work, right?

But there’s a growing trend that’s going against the ‘norm’ of high-carb running. A trend that even goes as far as to completely disregard the now sacred pre-race carb load….Sacrilege I hear you shout! This new wave is nothing new, of course. Low carb/high fat has had its various incarnations over the years. It comes around in cycles in various parts of the world and this means that it ends up in sport too. 

You may have heard runners such as the USA’s Jeff ‘Bronco Billy’ Browning, or Zach Bitter speak in-depth about their fat adaptation for ultras on various platforms. Or closer to home we have multiple Spine Race winner Eion Keith who opts to train and race in a low-carb state. Even Tom Evans has admitted in the past to using a modified low-carb approach to training and racing. If you ask the question, you may find that more ultra-runners than you think have at least tried an LCHF approach at some point in their training. They might not be doing it now or they may have their version of it. But it’s definitely a trick that a lot of runners at least want to have up their sleeves, even if they only try it out once. 

So if the pros have been doing it for years, why haven’t we? Are we missing a trick?

Should we be trying to get fat adapted for ultra-running performance? 

What is fat adaption?

Firstly, what exactly does it mean to become fat adapted from a dietary standpoint? 

Well, in layman’s terms the theory goes like this. The runner restricts daily dietary carbohydrate intake to a significantly low enough level, usually around 50 grams, which is the equivalent of 2 normal-sized bananas. This then triggers a metabolic response to increasing fat burning to produce the daily energy requirements that we need. It’s way more complicated than that, but it gives you the idea for now. 

The thinking on the benefits of this for ultra running is that if you can get your system to burn more fat at a higher running intensity, it relies less on the finite supply of glycogen that we can store in our working muscles and liver. Around 2-2.5 hours worth approximately. The logic says that if you can burn more fat, you’re burning proportionately less glycogen and you can run for longer without depleting your limited stores and the associated slump in energy, or ‘hitting the wall’ as it’s commonly called.

The other supposed benefit is statistics. Studies have shown that the number one reason for a DNF in an ultramarathon isn’t injury or under-training, it is in fact GI issues. Without being too graphic, our stomachs have had enough and it results in it coming out of us in one of two directions. The logic of becoming fat adapted in this case means that overall your fuel intake goes down during a run because you are relying more on your onboard energy supply in the form of fat turned into ketones. Less fuel uptake via your GI system means less irritating it and results in better performance overall. Sounds good, right?

Become a fat-burning machine!

If you’ve been into ultras for some time you may have heard this term thrown around. Become a fat-burning machine! Optimise your fat-burning potential! Outlast the competition! So you may have also then asked the question: How exactly do I become a fat-burning machine? 

Low carb, high fat. Keto, fasted runs, OMAD (one meal a day) bulletproof coffee, shots of MCT oil and the carnivore diet. These are just a few nutritional ways that are designed to get you there. But let’s not forget that years of consistent training will also get your machinery opting to burn a higher rate of fat over glycogen during submaximal efforts anyway. Running economy is one of the measurable facets of our running that increases exponentially with years of consistent training, as opposed to something like VO2max which has a genetic ceiling.

But are years of consistent training even needed? Or can we ‘skip to the good part’ as social media tells us? Can we shift our input to shift our output? Can we become the fat-burning machine that outlasts and outruns the competition? 

Well, I’d like to give you my N=1 experience.

Anecdotal evidence

There’s a saying that you may have heard quoted: “The plural of anecdote is not data”. Which of course is absolutely true.

Lots of N=1 stories of people transforming their running with a low-carb approach doesn’t mean that it’s the perfect diet for an ultramarathon, or even that it’s perfect for you specifically. But what if it is right for you but you haven’t tried it yet? Nothing ventured, nothing gained right? 

My own experiment 

Back in 2018, I had been running ultramarathons for about 3 years. Off the back of 10 years of triathlon, I worked my way up from marathon to 50K, 50 miles and 100K. What I noticed was that as with triathlon, I was ok at it. Not the best but certainly not the worst. I was the happy mid-packer for a while but I wasn’t content, I wanted more! 

How come I’d put in years of endurance training but never won a race? What made the guys and girls at the front faster, more able to endure? Why did I fade in the second half of my ultra when the winners seemed to just coast on without their pace deteriorating? I went on an internet search-quest to find the answers.

What I found was some references to a physiology study done in the US by Dr Jeff Volek on fat burning in elite ultramarathon runners. The 2016 study seemed to show a correlation between the low-carb diet and higher than usual fat oxidation at submaximal efforts. In some cases, the output was almost double an athlete who followed the traditional moderate to high carb intake. 

Some more searching led me to Zach Bitter's podcast, The Human Performance Outliers Podcast. In this podcast were all the answers I needed. Zach had himself transitioned to a low-carb approach and he had seen some amazing results, even some US and world records broken while he was on the diet! I did my due diligence and started to experiment with the diet in my own running. 

It was a disaster! 

I went cold turkey (pun intended) and immediately switched my diet from the traditional moderate to high carb, to super low carb. The result was three days of eating mostly tuna and eggs, which unsurprisingly coincided with three days of feeling absolutely lousy! 

I’d removed my body's preferred fuel source and it wasn’t happy. By the end of day three, I had to stop halfway on my usually easy run-commute home. I phoned my long-suffering wife and asked her to come and pick me up. I was done, finito, not one more step.

What I’d failed to realise was first, going cold turkey and expecting to carry out my usual daily activity and efforts were out of the question. I then learned that it takes at least two weeks minimum of adaptation to switch and during that time normal training should be kept to a minimum and reintroduced slowly and carefully. I also failed to realise that if you remove a major macro such as carbs, you need to replace it with another macro that can provide the required energy loss. In this case, obviously, I needed to ramp up my intake of healthy fats. 

My conclusion 

Long story short…..it took me a few months to adjust but these were my N=1 results:

1. I lost over a stone in weight which made me feel good about myself, especially since I was on the heavier side for my age and height. 

2. My tempo runs and speed workouts improved. Was this the reported ketone rush that people were reporting to experience? Or was this simply because I’d lost weight and my power-to-weight ratio had gone up? 

3. By far the biggest benefit that I saw was that I could now keep an even sub-maximal pace during races without hitting the wall or fading.

At my next 50K ultramarathon I sat back and kept my pace within the range I knew I could sustain for the duration. As the race went on I found myself catching up with the top 3 runners. Was I speeding up? No, I was just reeling them in as they slowed or bonked from their efforts. 

I went on to win that race and since then I’ve been fortunate to win quite a few more races with my newfound ability. 

So this begs the question: Was it the diet switch? Or was it the weight loss? Was it me training harder once I saw my pace increase? Or does the fat adaption process allow you to skip the years of consistent training and ramp up your running economy way quicker than usual? 

I’ve since tried other dietary interventions to help my running. But keeping my overall carbs lower than the average ultra-runner has been the one that has stayed the duration. 

Do I think it was a defining point in my running and racing career? Well yes, I do think it helped and I’m glad I tried it because it at the very least gave me a greater understanding of how the body's energy systems work or fail to work at times. Am I recommending it to everyone? No.

But like I said earlier, nothing ventured, nothing gained, right?