Adventures in Distance Running and Keto: How To Run Far on an LCHF Diet

In this post, I’m going to share my experience and advice in adopting the keto diet for 10-14 day cycles as a distance runner.   We’ll explore the background of ketosis, explain the potential benefits, and address the nay-sayers.  Interested in keto and running? Let’s jump in!

The principle behind the ‘keto’ diet is that you eat a lot of fats and very few carbs (LCHF = Low Carb, High Fat) in order to starve your body of readily-available carbohydrate energy and force it to use fat as its primary fuel source.

Mentioning the keto diet to a group of runners is likely to raise a few eyebrows.  After all, carbohydrates are our primary fuel source! It’s why we eat a carb-rich meal the night before a long run.  

In my half marathon and marathon training programmes, I’m a big advocate of using carbs as your primary fuel source – and explain the quantities and timing of how to maximise their effectiveness. 

That banana you grab before your early morning run?  Carbs.

Those gels and sports drinks you rely on to power you through a hard session? Carbs.

So why would any runner choose to cut carbs out of their diet altogether?   Needless to say, there’s plenty of skepticism on the idea.

I’ve now done several cycles of reaching ketosis – the state of when your body is producing ketones to burn fat due to lack of glycogen from carb sources – and wanted to share my findings and the potential benefits and drawbacks of going keto and running.

Let’s jump in! (warning: long post ahead…)

keto and running

The Ketogenic Diet – The Basics

The idea behind the Ketogenic Diet, or ‘going keto’, is that by cutting out carbs your body starts to turn to fats for fuel.  You begin to produce ketones for energy (derived from fat) as opposed to glycogen which mainly comes from carbohydrates. 

When you reach the state of ketone production, you’re officially in ketosis – you’re using fat as your primary fuel source.   You can check whether you’re in ketosis using a couple of methods I’ll explain later.

Going keto has similar effects to fasting, with a couple of differences:

  • You can still eat, you’ve just got to consume very few carbs and more fat.

  • Once you’re in ketosis, you can stay there as long as you’re willing…unlike fasting, where you’ll eventually need to break your fast if you want to live!

At this point, you’re probably thinking that keto is going to screw up your energy levels – and you’re right, but only while you transition to becoming a fat burner.  Then they actually improve – let me explain why…

The Benefits of Keto and Running- Why I Do Keto Cycles:

Every 3-4 months I go through a cycle of 7-10 days of ketosis, following a LCHF diet – I’ll get into the nuts and bolts of how to do it effectively later in this article, but for now…let’s address the reasons why I do it:

(quick note:  I’m not a doctor, the following is for informational purposes only, experiment at your own risk!)

Improved fat adaptation   

Anyone reading this who has ever Hit The Wall in a distance running event knows what it’s like to run out of fuel.  When we’re pushing it hard in a longer run, our body is getting the majority of its energy from glycogen reserves – which come from eating carbohydrates.  Hitting the wall means you’ve burned through all that readily-available glycogen and your body has to turn to another fuel source: fat.

If you’re a short-distance runner or usually consume a lot of energy gels as you run, your body probably isn’t accustomed to using fat as fuel source – so when it tries to suddenly switch to using fat to fuel your hard performance, it struggles.

That’s what ‘The Wall’ or bonking essentially is; your body has exhausted all readily-available fuel, and is now struggling to meet the demand.

If you’re somewhat fat-adapted, then The Wall can essentially disappear.

My experience has been that by performing regular keto cycles, those fat adaptation benefits have carried themselves over to my regular, non-keto life.   In other words, I can go for steady-state long runs that last for hours (fuelled by carbs first, fat second) without getting fatigued. 

This is what I attribute my improved performance in multi-day stage racing to: it’s actually been shown that in self-supported stage races, runners end up in ketosis whether they like it or not.  It certainly explains why I felt so terrible on days 3 and 4 of my first-ever stage race.

And it’s probably why now I am so much better at them; by day 4 of a week-long event, I can steadily conquer a 70-80km run while the other front-runners start dropping like flies (see my Namibia Race Report).

namibia keto for runners
200k into a 250k self-supported stage race, and in 3rd place: is it as much a ‘fat adaptation’ competition as a running event?

Improved sleep and energy levels

The first few days of keto adaptation are a drag as you starve your body of carbs – I cover this more later – but once you come out the other side, you can expect your day-to-day energy levels to be much smoother.  I describe it as less peaks and troughs, more of a steady-state flow

When I’m in ketosis, I fall asleep quickly every night and wake up feeling good, immediately ready to start the day. It’s easy to go for an early morning gym session or run without feeling pangs of hunger or low energy.

That mid-afternoon slump you experience in front of your computer?   Gone.   

While you still get tired and will always need down time to relax and recover, keto can bring you levels of mental clarity and energy.

Fat loss  / Body Recomposition

Yep, if you go keto then you’re going to start burning any excess fat fairly quickly.  You get a nice lean feeling once you get keto-adapted. 

Worried about muscle loss?  Don’t be. Studies have shown that as long as you eat protein with your fats and don’t just fast, you’ll maintain strength and muscle (and can hit the gym).

Potential wider benefits: anti-cancer effects,  aiding in heart and brain health

There’s a glut of studies which suggest much wider potential benefits of adopting a LCHF diet, including suggestions that 1-3 fasts per year could purge pre-cancerous cells.

More on the wide-ranging potential benefits here (I’ll leave this to the experts).

It’s in our blood

While it’s easy to dismiss Keto as the latest in a long line of fashionable diets, the state of ketosis is something that was a big part of our ancestors lives (as Nassim Taleb explains in Antifragile).

As hunter-gatherers, it’s been shown that we had irregular eating patterns – meaning we could go for days without a real meal, then gorge on a huge feast when an animal was captured or a new source of food was found.

And cultures across the world have included fasts of one type or another in their calendars for millennia: without worrying about about the potential origins or reasons for fasting, the health benefits are well-documented – it’s clear it’s something that has worked and had a purpose in society. 

keto and running

The Downsides of Keto and Running

Diminished Performance  

If you’ve read this far and are officially keto-curious, then a warning:

When you’re in ketosis, your athletic performance will likely suffer.

Don’t expect to jump into ketosis and set new PRs, or run your longest distance ever.

In fact, expect the opposite.

Carbohydrates are still the best source of fuel for high-intensity cardiovascular running, and without them you simply won’t be as fast.

What ketosis is good for is training your body to become a steady-state machine, able to go at a comfortable pace for hours without getting fatigued.

Endurance researchers have likened ketosis to removing your top gear; you can go for hours in an endurance state, but when you try to kick into a sprint you’ll find your abilities are restricted.

No Guaranteed Endurance Benefits

In other words, the sports science community are far from reaching consensus on the effects of a LCHF diet.

Many of the studies done to date are relatively small scale and inconclusive, or simply highlight the diminished performance capabilities of an athlete in ketosis.   

Much like the benefits of cold showers or the footstrike debate, there’s strong anecdotal evidence for both sides of the keto argument.

The non-performance-related benefits of ketosis are better researched and documented; I can recommend Dominic D’Agostino’s blog as a good source of information.

Keto Adaptation Takes Time

Getting into ketosis takes a few days, especially the first time you do it. And those days tend to suck.   Prepare to be moping around with low energy and enthusiasm and restless sleep as you starve your body of the easily-available fuel sources and force it to begin converting fat to fuel.   

Note: it can take weeks after you enter ketosis to become properly fat-adapted, wherein your body starts burning fat more effectively than it does carbs (source).

The good news is that there are steps you can take to speed up the process to get into ketosis, which I get into below!

What Do Other Runners Say About The Keto Diet?

When getting into something as complex as the keto world, I find it helpful to look around and see what other runners are saying about it.  Needless to say, there’s a mix of attitudes towards combining keto and running

1. The Marathon Training Legend – Hal Higdon On The Keto Diet

Hal is not only a legend, but has served as an ongoing inspiration to me as a marathon training coach. 

His thoughts on the keto diet are pretty black-and-white: he sees no benefit to it.

hal higdon keto 1
hal higdon keto 2

Hal’s comments echo those of many distance runners and coaches – that there’s no advantage to starving ourselves of carbs when they’re our primary fuel source for runs.

However, it’s clear that Hal is talking about applying the keto diet to periods of intense training (i.e. marathon training), and in this case I’m in agreement.   

When you’re in training for a big event, the last thing you need is to layer on the hardships of embracing keto.   It would be like a boxer training for a big fight and choosing to tie one hand behind his back.

For me, my keto cycles are an off-season activity, which then serve to help my on-season training.

2. The Sports Science Guru – Alex Hutchinson On The Keto Diet

Alex Hutchinson is the Malcolm Gladwell of physical performance, especially when it comes to endurance sports (@sweatscience on twitter, check my notes on his book Endure here).

He’s my go-to guy to understand the latest sports science research, as he consumes the latest research papers and literature, then presents them in a way that runners can easily understand.

If you’re looking for an impartial, evidence-based take on ketosis and running, you’ll get it from Alex.   

And his latest take is that, well, the evidence is shaky – and there’s still a lot of work to be done:

“Those who race all out for four hours or less and care about every second, it’s getting harder and harder to escape the conclusion that an LCHF diet is (at best) not an improvement on conventional mixed diets.” (Outside Online)

It’s been nearly a decade since I started reading (and writing) articles about the theoretical endurance benefits of LCHF diets. During that time, I’ve certainly spoken to lots of people who swear by this approach. I think it’s a cool idea and theoretically plausible. And I understand that studying these things properly is a huge endeavor.” (Outside Online)

Alex seems intrigued by LCHF / Keto diets, and while he is skeptical that there are any potential benefits for anyone performing high-intensity or short-medium distance events, he acknowledges that things change once you get into longer endurance events.

3. The World Champion Ulta-runner – Zach Bitter

Zach Bitter holds the World Records for both the fastest 100 miler and farthest distance run in 12 hours (104.8 miles).  He’s also followed a keto-style LCHF diet since 2011.

“Whether or not I’m training, the piece that stays consistent in my diet is using fat as a primary micronutrient,” says Bitter.

“I fell in love with the sport but started noticing it was getting harder to recover. Big energy swings left my energy crashing.”

Zach now moderates his carb intake based on his training intensity, dipping in and out of ketosis as he needs. On high mileage weeks, Zach increases his carb intake with low-GI foods like sweet potatoes, melons, and berries.

How To Go Keto If You’re a Runner

Intrigued enough to try ketosis and see how it feels?

Before I explain how I get into ketosis quickly, let me just prime you by saying you should be prepared for about a week of low-energy, low-performance output. You may not even be able to muster the energy to work out some days – the keto transition is a big mood dampener. 

So ensure you schedule your first ketosis cycle during a block of time during which you don’t mind if your running suffers a little.

How long should you go keto for?

Some people live a full LCHF lifestyle and stay in, or close to, ketosis all the time – Zach Bitter being a great example.

For many people, including myself, it’s difficult to commit to a full-time diet of high fats and low carbs.   Plus, I like carbs – they fuel my faster runs. And when you add in social commitments and family, it can get tricky to stick to a restrictive diet all the time.

When I first started out experimenting with LCHF, I did an initial longer keto cycle of 5 weeks to get fat-adapted, and nowadays my cycles are much shorter.

That’s why I do keto cycles every 3-4 months. Each cycle lasts about 14 days, I try to transition into ketosis as quickly as possible, then maintain it for about a week so I can spend some time working out and experimenting with output levels while in ketosis.   

The secondary benefits (mental clarity, reported flushing of pre-cancerous cells, purported improved brain health, and longevity) are all associated with the fasting state you create by starving your body of carbs, and can be achieved with a short keto cycle.

How To Get Into Ketosis (Quickly)

So transitioning into ketosis kinda sucks.   

You’re basically starving yourself of carbs to force your body to make the switch over to burning fat, and that leaves you feeling pretty low energy and perhaps a tinge grumpy.  Some call this phase the “keto flu”, which I think is probably overstating it. You might get headaches, be hungry, have energy swings, and sleep poorly…but if you start to feel actual flu-like symptoms (body aching, significant fatigue, sweats) then that’s something else.

When you’re in this transition, you start to question whether or not keto is actually worth it, and that packet of cookies on your shelf start to look very attractive.

The good news is that the more frequently you do keto cycles, the faster you get at it.  During my last cycle, I took <36 hours to start producing a mild amount of ketones (the body’s fuel for burning fat) and get my energy levels into equilibrium.

The fastest way to get into ketosis is simply to fast, and add in some moderate exercise.

This way you don’t give your body anything to ‘chew on’, and it quickly diminishes it’s glycogen reserves.  I usually try to fast but often end up eating something high fat to combat restlessness.   

My Schedule For Getting Into Ketosis:

Here’s my 3-4 day schedule for getting into ketosis efficiently, and minimising the length of the painful transition. 

Day 0 (the day before I begin)

On this day I’ll either have a large lunch and skip dinner, or have a light, low carb dinner.  I’ll drink good amounts of water and get to bed early.

Days 1 – 4

I wake up early, make coffee with added MCT oil, and then go for a low-intensity run or long walk.   Depending on what my schedule is like, I’ll try to be out for 1-3 hours. (note: if you’re not accustomed to distance running, then walking for a few hours has a similar effect).   Drink plenty of water.

I try to eat little, but at times either I get either listless or frankly hungry – then I’ll dip into something high fat low-carbs like some eggs with guacamole or a spoonful of peanut butter. 

Throughout these days, I keep up my MCT oil intake and will typically take protein powder after exercise. 

Some keto practitioners recommend exogenous ketones; these are supplements that contain lab-produced ketones which can be useful for kick-starting the process.  They’re not something I’ve played with, but many keto cyclers rely on them. Just remember that they should be taken in conjunction with the other practices noted here (cut out carbs, do low-intensity cardio); relying on exogenous ketones alone will probably not be enough.

Remember, the idea is to starve yourself of carbs essentially – you don’t have to go to net carbs zero, but the less you eat the faster you’ll make the jump!

How To Know If You’re In Ketosis

There are a couple of methods of easily measuring your ketone levels – which indicate whether or not you’re in ketosis.

The best method is via a blood sample tester (here are a few on Amazon) which work by measuring the ketones in a tiny sample of your blood, retrieved by pricking your finger.   The results are pretty accurate.

Another quick and dirty method is to use keto test strips – they’re a simple strip of paper that you pee onto, and they change color based on the % of ketones in your urine.  The problem with these strips is that your hydration level seems to affect the result; the more water you drink, the more diluted those ketones are, which will give you a lower reading. Still, they are a good quick and easy way to see if you are producing ketones, without worrying too much about the actual concentration.

You’ll also notice a few physiological changes when you reach ketosis:

  • Your energy levels will improve, as will your mood
  • Any hunger pangs will disappear
  • Better sleep
  • Better mental clarity.

How To Maintain Ketosis

Once you’ve navigated the minefield of the keto transition, here are my tips for staying on-course:

  • Minimise carb intake. You want to keep your carb intake down to 20-30g per day.   I tend to find it’s easiest to avoid carby food altogether than try to count the grams and stay within a certain limit. If you stay in ketosis for a few weeks, you’ll become fat-adapted and can introduce more carbs back into your diet when you want to fuel.
  • Eat fats.   The second part of the equation is to eat a lot of fats; your diet should be 55-60% fats.  In other words, it’s not enough to simply cut our carbs – you’ve also got to focus on fats.   Eating too much lean protein and not enough fat can actually kick you out of ketosis, so stock up on butter!
  • No need to be greasy.   ‘Eat fats’ might sound like every meal should be bacon cooked in butter, but the secret to sticking with ketosis is finding a meal plan that you find sustainable.   Leafy greens are low-carb, so I’ll try to have a side salad of kale and spinach with some feta and olive oil with meals.
  •  MCT oil helps pack in some fat. MCT oil comes from coconuts and is a great source of fat – I throw a few tablespoons in my coffee to add fats between meals.   Note: I have a big coffee in the morning, then usually a decaf around lunchtime.
  • Stick to the same stuff.  Keto is a pretty restrictive diet, and the best way to ensure compliance is to make it simple for yourself.   Try to identify the foods that work for you early on, and eat them regularly.  Meal prepping suits keto. Sounds boring at first, but if you can dial this in you’ll find it easy to stick to the system.
  • Mind your electrolytes.  When you cut out carbs, you’re often also cutting down on sodium intake.  That’s why it’s important to be mindful of your electrolyte levels.   A couple of times during keto transitioning I’ve felt terrible mid-afternoon, and remedied it with a stock cube dissolved in hot water. 

If you reach the stage of fat adaptation after a few weeks, you can actually reintroduce more and more carbs – much like Zach Bitter does – and your body will use them as fuel, but still have fat as it’s prefered fuel source.

keto and running

My Keto Food Plan

Nowadays, I’ve got my keto plan fairly well mapped out- I’ve figured out what works for me and now it takes almost no effort to stick to keto.  Here’s roughly what my day looks like:

Upon Waking: Water with electrolytes and coffee with MCT oil.

Breakfast (3-4 hours after waking): Scrambled eggs with chorizo mixed through, with added guacamole and hot sauce.

Lunch: Meat with a leafy green salad on the side, add feta and infused olive oil for flavour

Dinner: Low carb soup or leftovers.   I usually find I’m not particularly hungry at dinner time while in keto.

For snacking, I rely on peanut butter (100% natural) a lot.   I take a teaspoon of that regularly. Dark chocolate is another good once-a-day treat.  I also take protein shakes after runs or workouts, and MCT oil in my coffees.

I tend to be wary of any snacks branded as Keto, or restaurant menu items claiming to be Keto – it’s always worth looking at what else is in there, they’ve often got more carbs than you’d expect and other junk in there to fill them out.

How To Work Your Keto Diet Around Your Family

Keto gets tricky when you share a household with family members who aren’t following the same restrictive diet as you.

In order to maintain a happy household, I’ve found two things that work well:

1. Be responsible for all food preparation.   

Living with someone who is following a weird diet is much easier to do when that person prepares all your food too. In other words, as well as preparing your keto meals, you should try to prepare the non-keto food for all the other household members.  

This way, you’re actually doing them a favor and making their lives easier.   It’s a lot of work, but if it keeps the house harmonious and means they support your keto efforts, it’s worth it.

2. Find Middle-Ground Foods

There are a few dishes you can prepare that satisfy both keto and non-keto palates, though they require some planning. Our household favorites include low-carb spicy chicken broth (I add noodles for the non-keto people) and Thai green curry (I prepare cauliflower rice for myself, and regular rice for the non-keto members of the house).

Keto and Running – My Findings

1. Keto boosts my fat adaptation –  and hence endurance

On my last keto cycle, I woke up at 0600hrs on a Saturday morning and headed out the door for a 20k run, fuelled only by a cup of coffee.   Two hours later I was back home and felt great – throughout the run I’d kept my exertion levels to around 60%, and experienced steady energy that made me feel I could’ve kept going. 

If I’d tried the same workout in a non-keto state, I know my energy would’ve bombed about 40-60 minutes in, once I’d burned through whatever fuel was in my tanks.

I like to think of my keto cycles as exercising that fat adaptation muscle – it primes my body to burn fat more easily, and this pays off when it comes to several-hour-long runs, or – even more importantly – ultramarathons and stage races.   

(For the avoidance of doubt, I still fuel my long races with carbs, but that fat adaptation mechanism helps drive me forward when others start to drop off).

2. Keto = Awesome levels of general energy

In daily life, I’m often in a battle against my energy levels, trying to map workouts and important work around periods where I know I’ll have plenty of energy. I usually end up experiencing highs and lows – driven by caffeine and carbs, typically – which creates a bit of imbalance in terms of productivity and mood.

When I’m in ketosis, this problem basically goes away. No hunger pangs, no post-lunch ‘carb crash’, just a consistent, comfortable level of sustainable energy throughout the day. 

I often work out early in the mornings – when I’m in ketosis, I find that I can wake up at 5am and head to the gym, and work out without feeling sleepy or low energy.

3. Ketosis limits your athletic performance

There’s no getting around this one; being in ketosis means your anaerobic capability is throttled back. 

It’s why I’d never try to set a new PR (like run a 5k in 20 minutes) while following keto – when you try to find that top gear, it’s simply not there.

4. Ketosis is an off-season activity

Unless you’re Zach Bitter, it’s probably not a good idea to attempt keto adaptation while you’re ramping up your weekly mileage or preparing for a running event.

Instead, keto cycles are something I recommend trying out in the off-season when you know demands on your body are low and you’re willing to try out something new.

I do several of these a year, and always do one during Sober October – when I typically do a month-long keto cycle.

I get why most coaches are not a fan of keto – it limits your performance, and it doesn’t necessarily benefit your running game directly. Those runners who get the most out of keto are definitely ultrarunners. Plus, keto takes a lot of compliance – there’s a lot of discipline and education required.

But for me, ketosis is another string in my training bow – I see it as another form of resistance training, much like running with minimalist shoes or with a weighted pack. It has benefits that cascade into several areas of life, and helps my distance running endurance.

Thomas Watson

Thomas Watson

Thomas Watson is an ultra-runner, UESCA-certified running coach, and the founder of MarathonHandbook.com. His work has been featured in Runner's World, Livestrong.com, MapMyRun, and many other running publications. He likes running interesting races and good beer. More at his bio.

6 thoughts on “Adventures in Distance Running and Keto: How To Run Far on an LCHF Diet”

  1. Hi,

    Love the article. I have been running for 10 years or so and came across LCHF earlier this year. I am 52 and always been in decent shape.

    I did do more running early this year, but in April switched to the diet for general health reasons. LCHF should be our diet permanently, so I have been on it ever since.

    I lost around 3 kg pretty much immediately, dropping under 65kg for the first time in around 10 years. I have set new PB times for 10k (18:16) and 5k (19:01). These are both by some considerable margin.

    I had given up longer races as I found sustaining the energy levels impossible and consistently ended up injured. My new found energy levels and general health improvements (everything you mention) have encouraged me to try and so another go at marathon on the way in October.

    I can’t recommend this approach enough, it optimised my weight, energy and general well-being. I get that a elite athlete looking for instant burn may not fit this but they complete a marathon in just over 2 hours! For most people I believe the advantages far outweigh any negatives. How many runners do we see with a small “belly” that does not shift…that belly will go immediately.

    Thanks for the article.

    Reply
    • Hey Phil,

      Those are some decent PBs!

      Thanks for your kind words and glad LCHF is working for you too – I want to do more about it on the site.

      Thanks,
      Thomas

      Reply
    • Hi Phil, i have been on keto since may, im preparing myself to my first marathon in feb. 2022. My q is how do you fuel your body during a race day? Do you stay on keto o fuel with some carbs?

      Best regards.!

      Reply
  2. I’m going into my 4th week of LCHF. It’s revolutionised my life.
    Within days my stomach was flat and I have lost 3kg. The most amazing thing for me is my mental clarity and constant energy. Life changing! Running wise…. Still to be seen. But I don’t have those post run energy slumps and today I did a 20 k run and could have kept going quite happily. I also notice that my breathing is less laboured when I run now. I think I’m the next LCHF convert!

    Reply
  3. Thomas,
    I am a 62yr old recreational runner, with one marathon. I have been experimenting with LCHF diet for awhile. I really appreciated your blog, seems right on target to me. One tool for measuring ketosis that I recently purchased is from biosense – it is a breathalyzer. Just had it for about a month but I feel that it is pretty accurate.
    I have a question for you – I was curious if there are any supplements out there that improve the fat to energy process. A fat burner that kicks in to amp up the energy from Ketosis?
    Loving your website !

    Reply
    • Hey Scott,
      I know in the States a few companies sell Exogenous Ketones (basically a consumable version of the stuff inside you which turns fat into fuel when in ketosis) – that’s the nearest supplement to what you’re describing that I am aware of.

      Thanks
      Thomas

      Reply

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.