Best way to fuel? Carbs. vs Fat

I’m currently studying nutritional therapy, and one of my big interests-of course-is sports nutrition. However, I find the sector to be a bit of a minefield, with a huge range of varying opinions on all sorts of topics, particularly in terms of pre/post workout nutrition.


I have always been of the opinion that long distance endurance activity of any type is best fueled with carbs, carbs before hand, carbs during, carbs with some protein for recovery. Carbo-loading-which I love-for days before a race. Lately I’ve come across a lot of information that has challenged this view, so I’ve been trying to do some research and get my head around this area.


Initially my interest was peaked in the carb vs. fat debate when I listened to the marathon talk episode with nutritionist Barry Murray. Although he comes from a paleo perspective that isn’t really in line with my views in dietary terms, what he was saying about being fat adapted actually made a lot of sense to me. Basically he suggested that anything that is long endurance steady state based rather than high intensity is fueled by our own body fat stores, and if we pump our bodies with carbs beforehand and during we are affecting our bodies ability to access and burn these fat stores. This really makes a lot of sense when you think about it, as our body can only store limited amounts of carbohydrates, but we have a much bigger store of fat.


I went to a talk by Shona Thomson a while back at Ellis Brigham Mountain Sports, and again her PT David Arnot suggested that anything endurance based needs to be fuelled with fat- great more nut butter I thought!! Of course I need to be careful nutrition wise because of my Vegan diet to ensure I’m getting all my nutritional needs met, but I don’t see any reason why I couldn’t switch to trying to become more fat adapted. Of course I’m never going to make the complete jump to being fully fat adapted as that requires a total diet overhaul, and ultimately for me I love carbs, and they provide me with so many nutrients for my Vegan diet, however I am hoping that tweaking the way I fuel before and during a run might have benefits, particularly in longer distance races.

Over the last few months (when I have been running) I have been gradually trying to incorporate things on this front to try and get my body switched over into fat burning mode. Instead of having fuel before every single workout, I now try and run shorter low intensity workouts on no fuel first thing in the morning. It’s a hard thing to get your head round initially because the habit is so engrained. I found it tough at first because I don’t tend to eat late at night and usually wake up hungry, so it’s taken a while to get used to just heading straight out the door. If I am super hungry then I try to have a spoon of coconut oil, instead of grabbing some dates or a banana like I used to.


For longer runs I find that getting out of the habit of eating porridge is a hard one, as it has always worked for me, and is part of the pre-long run routine. I have stopped taking on extra fuel during runs though, and have run up to 12 miles without any extra gels or anything else during the run, again it’s just about getting used to it, and getting out of the mindset that you need fuel just because it’s what you’ve always believed to be true. It’s just about realising that the body has enough fuel to sustain you, but you just need to access it, and by constantly taking in carb/sugar before a workout this process is blocked.

I think it’s a long process to switch over and get your body used to doing something differently, and ultimately it’s just something I’m testing out to see how it works. I don’t believe in approaches being one size fits all, and I think everyone should do what works for them, so whether that is fuelling with carbs or fat do what is right for you. I’ll be really interested once I get back to running properly injury free, whether I notice any real benefits or differences by trying to make the switch.

Thoughts on fuelling with carbs vs fat?

9 Responses to Best way to fuel? Carbs. vs Fat

  1. I run all of my morning runs without fuel unless they are over about 15 miles. (I always eat before a race-usually a peanut butter bagel.) I never feel as though I have quite as much energy as when I’ve eaten a couple of hours beforehand though.
    It would be really interesting to go to a nutritional lecture at some point and I feel I would learn a lot.

  2. I definitely think this is an interesting debate, I know I tried having coconut oil before working out, but for me working out on an empty stomach as I rarely do anything endurance works for me.

  3. This is so interesting Lauren. I heard that interview too, and it made sense, although as a vegetarian it was hard to think about what sorts of foods I should switch to.
    I used to take on a lot of fuel, and mainly carbs- porridge before a run, a nakd bar and/or jelly beans during a half marathon, but they often gave me stomach ache and I hate that feeling in my mouth after eating something really sugary. I started going out before breakfast for 3 miles, then gradually upped the distance. I did then start having a few dates or something if I was going over 8 miles, but then stopped that too and like you managed 12 miles before eating anything. I am not sure what to do when the distances of runs get longer though- am thinking I need to find something more fat based to eat, but neat coconut oil makes me feel a bit sick too.

  4. I think I’ve become fat adapted recently, I’ve noticed a huge difference in my hunger levels (I can go for hours and hours without eating). I’m actually really undecided about my half marathon because I usually have an oat based bar or two for a half, yet haven’t eaten oats for a year! My fats come from olive oil in cooking and drizzling, so much nut butter and coconut yoghurt, tahini too. I’m not sure any of those would work pre long run!
    I can’t tolerate too much coconut so a spoonful of oil wouldn’t work for me. But in general, at least half of my diet is from fat most days.

    • Yeah I think it’s supposed to make a big difference, I guess you don’t have the blood sugar highs and lows. Yeah I’m not sure either, I’d probably just stick to the bars if they work for you.

  5. Like you I found that Marathon Talk interview very interesting.
    If I run in the morning I’ll always run on an empty stomach purely because I don’t want to get up any earlier to eat something. I’m usually quite hungry (always am whatever time I wake up) but as soon as I start running I’m fine. It is interesting about they say about having enough fuel within us but not being able to access it.
    For Berlin I was going to play around with my nutrition but not having had the chance really to put anything into practice I’m going to stick with what I know. Breakfast beforehand, three gels during (though I’ll see how I feel – definitely take at least one) and then ALLTHEFOODS after 😉

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