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Eating to Fuel Endurance Training and Long Distance Races

A subject I am often asked about is ‘what is the best food to eat for marathon training, ultra-marathon running, Ironman training’ and so on. I have lots of friends involved in endurance sport, and I have a reasonable amount of experience myself, and there is a lot of confusion and misunderstanding about fuel for endurance sport. Personally, I have been in long distance endurance events with far more experienced runners than myself and seen them fail and drop out because they ‘got it wrong’ with their fuel, yet in my own experience, such problems are entirely avoidable most of the time.

This post will explain:

  • Why complex carbs are not the best fuel for endurance races
  • Why complex carbs are not required in great quantities pre-race (carb loading)
  • Why gels and bars are not the best fuel to consume during a race
  • How to be ‘a fat burner’, not ‘a sugar burner’
  • Understand how to unlock thousands of calories of energy for long races

First of all, I think you might like to start by reading my ‘intro post’ on running: https://mothernaturesdiet.me/2013/08/26/838/ It’s quite short and simple, and briefly explains why I prefer trail running to road running.

I was recently asked if I had experienced any problems when I switched from a ‘typical’ runners diet (high in complex carbs) to a low-carb ‘paleo style’ diet – did I then find myself getting close to a ‘bonk’ when training or racing? Now you might ask ‘what is a bonk?’ While some may think it sounds like fun, sadly it’s not that kind of a ‘bonk’!! Endurance athletes have several expressions for this, you will often hear marathon runners talk about ‘hitting the wall’ or you may have heard some endurance runners talk about how they “got X miles in then crashed” or “I blew up at X miles”. Bonk, or ‘hit the wall’ or ‘crash, or ‘blew up’ all mean the same thing, it’s when your body runs out of energy completely, your blood sugar level hits ’empty’ and you get all dizzy and have nothing left inside you. This is when endurance athletes are often forced to drop out of a race, and they have to declare ‘DNF’ = Did Not Finish, the last thing any of us ever want to see on the Race Results Sheet! All that effort, training and preparation, the excitement, the build-up, the anticipation, ending in a DNF is soul destroying.

Most (a generalisation, yes) endurance athletes use these sports gels and energy bars to keep themselves fuelled during long distance events. The majority of sports gels are basically just a blast of sugar, a little water, some minerals and often a dash of stimulant, such as caffeine. I could write an extensive post about gels. We could talk about how the minerals are essential to replace lost electrolytes, without which you could face painful muscle cramps in your legs, which can be agony, believe me. We could talk about the pros and cons of stimulants. We could talk about the artificial ingredients, and the healthier home-made alternatives. We could talk about how many athletes consume lots of these gels or energy bars then end up DNF on the side-lines of the race, vomiting with painful stomach cramps. But this post is about racing without gels, so we will leave all that for another day.

First, the science bit

In order to understand how to best fuel our bodies for long distance races, first we need to understand how our bodies metabolise sugar and the role of insulin in this process.

https://mothernaturesdiet.me/2013/11/03/sugar-and-the-insulin-response-in-plain-simple-english/

Sorry to send you off there to read that little bit of extra background reading, it just seemed easier to give you that link, rather than re-write all of that here again in this post.

In a nutshell, when your body has glucose floating around in the blood, you will also have insulin in your blood too. Keeping the science to a minimum now, and talking in very basic terms, the role of insulin (which is a hormone) is to file nutrients away where they belong. Insulin does many things, and helps to send various nutrients where they are supposed to go, but for the purposes of this thread, the main role of insulin is to clear those excess blood sugars (glucose) out of your blood. It will help push those sugars into your muscles if they need it (which obviously they do during a marathon or Ironman) and then it will take any excess glucose and push it into fat cells for storage.

So in that link above, you read about how insulin sets up your body chemistry in a way that creates a ‘one way door’ into your fat cells. When insulin is present in the blood, in reaction to the presence of glucose, those ‘one way doors’ into fat cells are open for glucose (energy) to flow IN not OUT.

Eating on the run

If you are eating carbs (such as gels and energy bars) during long training sessions or on actual races, then the sugar quickly reaches your blood, insulin is triggered, and your muscles start sucking up the glucose. Essentially, that is all good, your muscles need the fuel. Fuel = happy muscles. Those muscles will keep going until the build-up of lactic acid ‘blocks up’ the muscles so completely that they have no space left to take in further glucose, at which point you either need to stop, get a massage, rest, hydrate and then go again, or fatigue ends your race.

However, there is another side to this story. I see a lot of runners on marathons and ultra-marathons setting off with masses of gels at the ready. After the first hour or two has elapsed, they start taking a gel of a half of an energy bar roughly every 20 or 30 minutes, the idea being to keep fuelling the muscles. Eating those carbs constantly, means that insulin is pretty much constantly present in your blood. If insulin is constantly present, the one-way-door to your fat cells is permanently open for IN, not OUT. This means that your body can never access your fat reserves as a source of energy. There are tens of thousands of calories of energy available in body fat, even on a fairly lean person, and yet while fat cells are in ‘receive’ mode, not ‘give’ mode, those energy reserves remain totally unusable.

In order to access fat, your body chemistry needs to be set up to burn fat. The one-way door needs to be set to OUT, and they won’t happen in the presence of insulin.

If you are running on sugars, it’s a game to keep putting them in every 20 or 30 mins. As soon as you stop, 20 mins later = bonk. I believe that this is what marathon runners talk about as ‘hitting the wall’. It’s when they have burned up breakfast, sucked down their gels, and their blood sugar crashes and they hit ‘empty’. They feel wiped out and they just can’t go on.

Now, all that above is pretty solid science. The rest of this post is based somewhat more on my own ‘experiential learning’.

If your workouts are anything up to an hour or two, for most people, I guess healthy complex carbs are a perfectly good source of energy. You eat some food, you go burn it off. Personally it’s not really how I train, but if that’s your style, then I guess that works for you. I believe that sustained aerobic exercise (endurance running, triathlon, etc.) needs a much better source of slow-release fuel, and if you are trying to fuel serious workouts, like the 10 to 14 hours required for an Ironman or ultra-marathon, then trying to cram in enough food to fuel that will always be hard work. Rather than trying to eat all those calories in the hour before the race, or during the race, doesn’t it make much better sense to dig in to your existing energy reserves, your body fat? Your body carries tens of thousands of calories of fat, so that would be the perfect fuel, if you can train your body to access it, and set up your blood chemistry the right way.

To access that fat, you need to open those one-way doors to ‘OUT’ not ‘IN’. In order to achieve that, you want to ensure insulin is minimised, so the best way to achieve this is to not eat sugars/carbohydrates.

In my opinion, the reason most athletes bonk, crash, burn, blow up or hit the wall, is because they load up on a high-carb breakfast on race day, after a week of carb-loading, and after months of training with carbs providing their main source of fuel. Come the race, they get 2 or 3 hours into the event, and start sensing that energy levels are flagging, so they start popping gels. The blood-sugar cycle goes round and round…sugar in, sugar burn…sugar in, sugar burn…til they run out of gels and crash. (As an additional problem, many of the endurance runners I know, suffer from gastro-intestinal cramps caused by eating all that synthetic gel rubbish – in my opinion it’s not real food! I have tried gels and bars, and some are OK, but I found that if I had any more than 2 or 3, they started to make me feel a bit sick. Real food never has that effect on me.)

To me, it makes much more sense to ‘train your body’ to use fat as the primary source of fuel. I have run a dozen marathons, 3 ultra-marathons, cycled John O’Groats to Land’s End (the length of the UK, 983 miles in 9 days), and yet I have never ‘hit the wall’ once. I have run for 11.5 hours non-stop over mountains, and cycled for up to 13 hours per day, but never DNF and never ‘bonked’.

I ran my first two marathons (Barcelona and Paris) as ‘a sugar burner’, because that was about the time that I was still learning about low-carb eating, and I still had a mental belief that I needed to load up on complex carbs for a marathon. If my memory serves me well, I took gels with me for those marathons. Then I learned about all this stuff and shifted carbs out of my diet and my training improved, my times got faster, energy more stable, I lost weight, and started finishing marathons in 3:40, not 4:20, and finished feeling like I still ‘had some left in the tank’.

Becoming a fat burning machine

By living low-carb all the time, over a period of approximately three months (training every day, often running and cycling, but some weights too) my body ‘learned’ to be ‘a fat burner’. I wasn’t eating carbs every day, except lots of vegetables and some fruit, but my diet was high in natural whole foods, eggs, meat, fish and veggies, and when I exercised, within no time at all, any available blood sugar had burned off, and my body was familiar with dipping into my fat cells for energy. I think it takes a time to ‘learn’ this behaviour. 

Your body adapts to things over time. Think about how people who weight train talk about ‘muscle memory’, saying that it is easier to build muscle you once had but lost, than to build new muscle the first time. It takes time to train the responses, to establish the preferred metabolic pathways. Just the way repeated aerobic exercise conditions your heart, lungs, legs and so on to endure more and work longer or harder or faster. The same way you don’t damage your pancreas the first ever time you eat a sugary snack, but decades of eating a high sugar diet eventually leads to type 2 diabetes. Again, just the way repeated anaerobic training with weight conditions responses such as increased strength, larger muscle mass and faster recovery. These are all examples of a ‘conditioned response’ in your body. And in the same way, I believe your metabolism can be trained to respond to a workload (in my opinion…as I said, I have not yet done all the research on this) and once you are used to low-carb living, and your body gets used to using fat as fuel, then it goes straight there every time. It becomes a conditioned response, a preferred metabolic pathway. A path well-trodden is easy to follow. 

Once your body learns that carbs are not coming in all the time, it will stop ‘seeking’ them as fuel source #1, and learn to use calories released from fat cells. In my experience (and not everyone will be the same, remember that), the more my body got used to not eating carbs, the quicker and easier my fat cells turned on and start providing constant stable energy. 

Now, here in 2014, and paleo diets are ‘all the rage’, I see loads of people eating low-carb about 70% of the time, then loading up on carbs for long weekend training runs and for events and races. I think problems occur when you are eating low-carb ‘half’ the time (meal times during the week) and then suddenly carb loading on the weekend and shoving carbs (gels and bars) in during long training sessions and races. I think your body chemistry gets ‘confused’, it isn’t sure whether you are a sugar burning athlete or a fat burning athlete. 

So I think eating low-carb is the best way to go for endurance sport, low-carb all the time, including pre-race, race day and during a race or event. POST event, then carbs are fine, shove in a ton of carbs soon and refuel your exhausted muscles. Post-training you should eat good carbs, especially in that 20 minute window of opportunity when your muscles are still highly receptive (pumped) then gulp down some fruit juice, dried fruit, a recovery or weight-gain shake if that’s your thing, or some dark chocolate. After the event, your energy systems are no longer trying to access calories from fat cells, you are now resting, and you want lots of glucose in your blood and all the insulin you can get, to ram those exhausted muscles full of glucose to aid recovery. Listen, I do not advocate eating junk food or consuming alcohol, but in all honesty, if you just completed something epic like an Ironman…well, if you want pasts, beer and ice cream, you go for it, your body will swallow up any calories it can. But post-workout is the only time for sugary carbs, in my opinion. The rest of the time, I get my carbs from vegetables and fruit only. 

Copenhagen marathon PB aged 40

I have run 12 hour ultra-marathons over mountains fuelled on scrambled eggs and veggies. I ran the Exmoor CTS marathon and came first in my age group (vets), after scrambled eggs and sausages for breakfast, and a steak dinner the night before. No carb loading, and I won the event at age 40 and over. My personal PB marathon was in Copenhagen in 2011, where I ran a marathon in 3:14:17 at age 40. I had eggs and stir-fried vegetables for breakfast in my hotel that day. So the carb overload is not required, in my experience. On these runs, I take no gels or bars. Up to about 4 hours, I don’t need anything but water. On longer runs, I will snack on whatever is available at the aid stations on long races. In the UK it tends to be fresh fruit, dark chocolate or (worst option) biscuits, and I’ll avoid the biscuits if I can, preferring oranges, bananas or dark choc. In France they usually have salty meats and cheeses, hot salty soup (very welcome on a snowy mountain top!) and other excellent offerings.

Being a fat burner and competing in endurance events on a low-carb diet is not new. If you want to learn more about it, try Stu Mittleman’s book “Slow Burn”. He has run thousands of miles as a low-carb ultra-athlete and his book explains it all far better than I do, and in much more detail. But of course, what works for one person may not work for another. We are all different…I experimented with low-carb/fat-burner/endurance sport and it worked well for me, but it may not work for you. You have to try it out and see how you get on. This a fundamental point of ALL nutrition advice and ALL ‘diets’ and eating plans. A system or solution that works for one person, will not work for another, because we are all different. So you can only try each thing, as I have done, to find what works best for you.

 

 

 

34 Comments Post a comment
  1. David Perry. #

    Brilliant post this. I’m certainly thinking this is the way to go for long distance triathlon. Ran 2 hours 20 minutes this morning at 70-75 % maximum heart rate which seems to be the optimum fat burning range. Feeling easier every week on this low carb diet, legs hardly tired at all, reckon I could go again this evening, weight has dropped to 66.2 kg from well over 74kg in November. Just one question though. I can see how this works fine when working within aerobic limits but I’m just wondering how the body reacts on this diet when you start to go anaerobic for sustained periods, for example during a 10km road race. Will it still burn fat or will it look for sugars to fuel this harder effort? I’m not quite clear about this, can you clarify?

    January 19, 2014
    • Hi David, and thank you!
      Well, I might have to go into a bit of complicated science now, but I’ll try to keep this as simple as possible.
      1: Your muscles don’t actually burn glucose (or glycogen, the stored version of glucose), your muscles cannot directly burn either carbohydrates or fats.
      2: Enzymes actually break the glycogen down and convert it into something called adenosine triphosphate (ATP) which is the actual substance muscles use to power a muscular contraction.
      3: Your body only ever stores enough ATP to power a few seconds of activity, but the muscles are constantly converting glycogen into new ATP to power further work.
      4: Sensing a nerve impulse (the motor nerve trigger indicating the start of muscular contraction) ATP starts to split.
      5: As glycogen is converted to ATP, waste is produced, this is lactic acid. This process is known as glycolysis.
      6: If only glycogen is converted to ATP rapidly, then oxygen is not required. Because this process can happen without the presence of oxygen, it is referred to as anaerobic, not requiring oxygen.
      7: Fatty acids and glycogen can be constantly converted to ATP in the presence of oxygen, using enzymes, and the process produces carbon dioxide and water as by-products.
      8: The conversion of glycogen to ATP in the absence of oxygen only produces tiny amounts of ATP (2 molecules in each reaction), whereas the conversion of fat and glycogen in the presence of oxygen produces much more ATP (38 molecules in each reaction) and this explains why anaerobic efforts cannot be sustained for long, but aerobic activities can last much longer.

      So, what does this mean? Basically, if the activity cannot be sustained for more than about 1 minute maximum, then it anaerobic. If the effort can be sustained for longer than 1 minute, it is aerobic.

      So running, even if you are pushing the pace and running a hard and fast competitive 5k or 10k, is still an aerobic activity, and fat is still a good choice of fuel.

      Anaerobic running is 100m, 200m and maybe 400m sprint. All other run distances, are aerobic.

      Running at pace to complete a PB 10k, as against ‘plodding’ through a marathon, does not take you into an anaerobic state…it’s still aerobic, just ‘hard’ aerobic, which will help build your fitness!

      Does that make sense David?

      January 19, 2014
  2. David Perry #

    Excellent yes I see what you mean – thanks.

    January 19, 2014
    • Awesome! Keep me posted on how it all works for you buddy 🙂

      January 19, 2014
  3. Very interstitial g and perfect to I g after bonked after yesterday’s ride then it affected my run today leading to a DNF, I only had the energy to complete 5 of the 6 cross country miles.
    Will be reconsidering my diet with regards to fuel g my ironman training
    Thanks for post

    January 19, 2014
    • Hey Zoe, I saw your re-blog, thank you, and please, if you try changing your diet, let me know how you get on, stay in touch. Most people drop carbs and switch to eating more protein and fat, and getting their carbs naturally from veggies, and they report more energy, improved endurance, weight loss, stable energy levels and so on.
      I hope it works for you – stay in touch!
      Karl 🙂

      January 19, 2014
  4. Reblogged this on Swim, Sweat and Gears and commented:
    Very interesting read especially after my weekend bonk and DNF

    January 19, 2014
  5. Reblogged this on Fit Recovery and commented:
    An interesting perspective on endurance fueling indeed…

    January 19, 2014
    • Thanks for the reblog Jim – I checked out your blog too, very nice site! 🙂

      January 20, 2014
      • Thanks Karl. You too brother.

        January 20, 2014
  6. I find this fascinating how & when the body uses the fuel it receives. This is something I’ll be paying close attention to over the coming months as I want to get it right in race day and don’t want an armful if gels if I can possibly avoid it. I’m currently running 10k x 3 times a week fasted, what impact if any do you think this will have on my bodies ability to run in fat rather than carbs?

    January 20, 2014
    • Hi Beth,
      To be honest with you I have not experimented myself with training in a fasted state, so it’s not something I can speak about from personal experience.
      I did publish a little book – please download here: https://mothernaturesdiet.me/2013/08/13/the-mnd-guide-to-body-composition-free-ebook/ – which explains about the health benefits of intermittent fasting, that might interest you.
      From what I can see when I read about fasted training, and from friends I know who train that way, I think it has benefits for burning off body fat, but I don’t know that it is of any benefit for performance. Personally, I’ve never done it myself because I don’t feel strong when I am hungry. I prefer to eat a little something then train, but that’s just me – I train for fun and performance, not to burn away body fat.
      In terms of how training in a fasted state applies to this post, I am sure fasted training would simply speed the selection of body fat for fuel, because there will be no free glucose in the blood and also no insulin, so I guess it all helps.
      Stay in touch, let me know how you get on.

      January 20, 2014
  7. David Perry #

    It’s just that I understood that at higher aerobic intensities we burn more sugars and less fat – not true?

    January 20, 2014
    • David, maybe, in all honesty I just don’t know, I’d have to do some reading and research to answer that question for you. I know that lower aerobic intensity is perfect for fat burning – I.E. a full day of hill walking is the best fat burning exercise I have ever found.
      But I am not sure that your body will see much difference between running at 6 mph, 7 mph or 8 mph in terms of selecting fuel for that activity.
      I know your body will see a difference between “gentle jogging” and “all-out maximal effort sprinting”, but as for different levels of aerobic work, I think the metabolic pathways involved in the selection of fuel are going to remain fairly constant.
      If you have any research to the contrary please share it with me, as I am always looking to learn more!
      Thanks David!
      Cheers,
      Karl

      January 20, 2014
  8. David Perry. #

    No I don’t know much about the science of all this – just things I’ve picked up from reading, some of it contradictory. What I have found since going low carb, apart from the weight loss, is that my heart rate remains a lot lower than before, even when doing spin sessions flat out or interval training for running and it seems hard to attain the same level of suffering as before! Also found recovery much quicker. Guess it’s mostly trial and error, see what works. Ultimately it’s about health and lifestyle for me, although improved performance is always welcome.

    January 20, 2014
    • That’s interesting David, and of course, it could all just be linked together – weight loss, better body composition, improved cardio-vascular fitness, heart working more efficiently – all results of your body saying to you “Cheers David, I like the new diet, it suits us, I feel great!”
      Well done to you mate! Keep it up!
      As and when I find out any more myself, you’ll certainly be among the first to know! 🙂

      January 20, 2014
  9. Trails and Ultras #

    Very very interesting. I don’t get on with gels at all and prefer real food on ultras but could I cut down on carbs that much in normal life? Not sure. Thanks for a great post 🙂

    January 20, 2014
    • Thanks Anna, I agree, I don’t like gels, and real food provides the electrolytes too, so it’s win:win all round for me! Good luck with your 2014 running!

      January 20, 2014
  10. Great post. As a fellow ‘caveman’ I completely agree with the training time to go from a sugar to fat burner and utilizing body fat for fuel. I have done it effectively for over 2 years now.

    One point to add to David Perry’s thoughts; your body can only go so fast when using fat primarily for fuel.

    Going from aerobic to anaerobic (it is actually more complicated than that) requires your body to tap into it’s glycogen stores which are replenished by simple or complex carbohydrates. Which one you choose it based on the situation; simple for mid-race (fast absorption) and complex for post training (slower absorption).

    It obviously depends on the person as you demonstrated with a 3:17 marathon. I am definitely not that good at burning fat, I would be anaerobic for sure.

    January 20, 2014
    • Hey Steven, hello to you in Canada, good to hear from you, thanks for your comments.
      Yes, you are right, but I think that switch up to anaerobic happens at a way faster pace, IMO. Anaerobic, by definition, means a pace you can only hold for about a minute…anything sustained for many minutes is aerobic activity, and will follow the same metabolic pathway, converting glycogen (stored glucose) to ATP in the presence of oxygen. But as you say, we are all different, and I think that’s a really important point people need to remember, we each need to find what works for us, and it won’t always be the same.
      All the best, keep on running caveman!
      Karl 🙂

      January 20, 2014
  11. Hello to all, it’s truly a good for me to pay a quick visit this
    web page, it includes valuable Information.

    April 11, 2014
  12. Harold #

    Hi David ,

    I’m doing the kokoda challenge in a couple of weeks. Do you have any tips that will help us on the day to assist in crossing the finishing line thanks ?

    July 5, 2014
  13. Harold #

    This is a 96 kms walk through the hardest terrain in Australia .We have 38 hrs to do the whole tracks .The highest elevation on the tracks is 600 meters .

    July 7, 2014
  14. David #

    Harold, I am by no means an expert in this field. I’ve been preparing for a 100kms Ultra for the last 6 months and planning to run it as much as possible, walking only on the steeper sections if possible. The reason is because it’s hours on the feet that really hurt so you want to finish as quickly as possible, otherwise, if you just walk, I’ve found that my glutes get really sore. Obviously proper hydration is crucial, especially in that environment – depends also on feed stations – how often and what do they provide? You want to carry as little as possible. Loss of electrolytes, especially salt is a big issue. Personally I don’t use sports drinks or gels because my body doesn’t like them and they don’t seem to help. I use coconut water, diluted with mineral water a lot and avoid fizzy drinks, sometimes use heavily diluted orange squash for variety. Although I try to stick to good dietary principles most of the time in my daily life, competing is slightly different for me and I’m open to anything that might help complete the task. I therefore use salted nuts and salt and vinegar crisps to replace the lost salts and avoid cramps. I use bananas for potassium and I also take magnesium and zinc tablets regularly. Other things I like to eat during an event or long training include: Nak’d berry bars, nut, seed, fruit bars, flapjacks, oranges, cheese, raisins, almond butter on crisp bread , but beware of the tendency to overeat for comfort, leaving you bloated. Blisters are also an issue for most people I guess, so be prepared to deal with or prevent those. Like I say, I’m still pretty much a novice at this myself, but hopefully this helps a bit. Good luck with the challenge – we are all capable of so much more than we realise and suffering brings its own reward.

    July 7, 2014
    • Harold #

      Hi David,

      Thankyou so much for all the tips and support, i will let you know how we go next week .

      July 12, 2014
  15. David Perry #

    Good luck mate.

    July 12, 2014
  16. Having read this I thought it was really enlightening.
    I appreciate you finding the time and effort to
    put this content together. I once again find myself spending a significant amount
    of time both reading and leaving comments. But so what, it was still worthwhile!

    July 16, 2014
  17. Reblogged this on MotherNaturesDiet and commented:

    In training for the 2014/15 marathon season?
    This is well worth a re-read…and since this was originally posted almost a year ago, there is now extensive additional value in the comments below.
    Keep on running!

    November 19, 2014

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