Cycling on a Low Carb Diet / Ketosis Update (before Christmas ruins everything!)

Cycling Ascents - Accommodation and Training Camps at the foot of Alpe d'HuezA quick update as promised, but I’ll keep it brief as we’re pretty busy (as I’m sure you are) prior to the Christmas holidays!

I’ve now been on my LCHF (low carb high fat) diet for around 6 weeks now, and despite not being in ketosis all the time (the state where your body is purely running on fat), I think I’m getting the hang of it.

You can test yourself (to see if you are in ketosis) a couple of ways.  I use something called Keto Sticks – you wee on them and then you compare the colour (of the stick, not your wee!) to a scale to tell you how far into ketosis you are.  Alternatively you buy a blood ketone monitor (which is much more accurate) but I’m not quite that far into it yet – watch this space though!

So with the help of the sticks and plenty of trips to the toilet, I’m slowly understanding what I can and can’t do, diet and lifestyle-wise to stay in ketosis.  Rather conveniently you retain less water on this diet so more of it goes straight through, resulting in more trips to the smallest room, hence lots of testing opportunities!

Knowing I’m in ketosis is important, as for any kind of sporting benefit (well in my limited experience, anyway) a ‘nearly there’ approach doesn’t work too well.  When fully in ketosis I feel good, when on the border but just out I don’t feel that great (nothing as bad as Keto flu though!) and that seems to translate back to not so brilliant performance on the bike.  So here are some observations (purely personal, and not at all scientific) on how this diet has affected my cycling / running / swimming:

  • good hydration is critical – as you retain less water it seems that regular hydration, during exercise, specifically with electrolyte drink is even more important than usual
  • it seems to take a little longer to warm up…by this I mean that while you should always warm up before a hard effort, if I really had no time then I could just jump straight in there without too much of a problem (ie connecting to Zwift for a race scheduled 5 minutes later was a stress but didn’t really affect my performance).  Now my lack of planning seems to cause more problems than it used to!
  • heart rate seems higher across the board.  Purely based on feel (I still haven’t don’t an FTP test!)  my heart is about 5 – 8 beats higher than I’d expect for a given effort, but less so at lower intensities.  This seems to be coming down – it was 10+ higher when I started, and at lower effort levels (zones 1 & the bottom half of zone 2) it seems nearly back to normal.
  • max heart rate seems easier to achieve – I’ve hit 185bpm a couple of times in sprints at the end of Zwift races…and it really is a maximum as when I look at a graph of heart rate over time it climbs with effort then flattens off.  I’ve not seen 185 since I won my only ever race in New Zealand 7 years ago! Whenever I’ve got anywhere north of 180 in the past year or two I usually feel like I’m dying…..however whilst no walk in the park in ketosis it doesn’t seem so bad somehow!  This might be a reason for the ‘flat line’ which I’ve never achieved before (in the past it rose to a peak then dropped after I stopped pushing).  Could be physiological, could be psychological as I’ve read somewhere that your pain threshold is higher in ketosis.
  • I’m getting the feeling now that I could go for a long time when I’m in Z2 (compared to before when I was feeling a little drained most of the time during exercise….probably due to my body wanting to know where all the glycogen had gone!)  This is unfortunately currently limited by my muscular fitness (i.e. I feel like the energy stores are there now but my legs don’t want to play ball).  This is a hint of the ‘all day’ endurance that I’ve been looking for!  However I need to stress that this is unproven yet…but once I get back into shape I’m keen to try it out.
  • I’m still seeming to have to breathe less heavily for a given effort – this has particularly helped my swimming as I’m now not feeling like I’m desperate for the next breath each time I come up for air (which is nice!)
  • It seems that I can eat some carbs and stay in ketosis as long as it’s just after exercise.  And the more intense / longer the exercise session, the more I can tolerate.  To give you an idea though, if I have a greek yoghurt with raspberries, coconut, and hazelnuts (one of my favorite snacks) after a hour of Z3 I’ll still be in ketosis; if I had it during a day when I’ve not exercised (especially in the evening) then I might be pushed slightly out of ketosis.  The next stage is to experiment with carbs during exercise…apparently this can boost your performance at the top end which is traditionally lacking from a LCHF diet (but hasn’t really seemed to be an issue for me…perhaps I’ve never had a top end!)

So to summarise, all seems to be going well.  My weight has stabilised at about 2.5kgs less than when I started, but still 2 kgs over my ‘race weight’ (when I’m at my race weight most people think that I’m ill, by the way).  More importantly, whilst I don’t feel like superman I’m definitely feeling better on the bike, and performance has taken an up – turn. This is unfortunately confounded by the fact that I wasn’t in the best of shape prior to starting this diet, so I’d expect to be getting a little better anyway.  But I can definitely feel that my long term energy levels are not dependant on stuffing carbs into my body anymore, and that my general feelings of well-being are a good enough reason to keep going with this diet.

Unfortunately Christmas (with all its associated carbohydrates) is looming, so I suspect I’ll get to see what it feels like to have a ‘Carbs Hangover’ pretty soon!

note – if you think this is something you’d like to try, I’m currently reading ‘What the Fat – Sports Performance’ by Grant Schofield, and can really recommend it.

You can read more about my low carb experiences here:

Part 1 – Exercise without Carbs

Part 3 – My Continuing Low Carb experience

6 Replies to “Cycling on a Low Carb Diet / Ketosis Update (before Christmas ruins everything!)”

  1. Hi, I’m very pleased to have found your site and I’m wondering how you’re doing with training in ketosis?
    I’m doing La Marmotte this year and decided to try the keto genic diet for pretty much the same reasons as you. I’ve only been on it for 24 days but have been in ketosis all that time (blood sticks). So far I’ve found that my 20 min power has dropped dramatically and that my HR is higher for any given effort like yourself.
    Have you found a way to discover if you are keto-adapted as opposed to just in ketosis. I’ve lost 12lbs which is obviously a good thing but my training is going so badly I’m beginning to panic.
    I’m off to Majorca for training/holiday on Thursday and may well revert to carbs. Any words of wisdom.

    1. Hi Terry, I don’t know if there is a definitive answer to your question, given that it’s probably an individual thing, but mainly because I don’t believe there have been any scientific studies on this (if anyone knows of one please let me know!) From my experience, it’s a little hard to say as after I wrote this blog post I eased out of ketosis into a less strict low carb diet until recently (I’m back in ketosis now). I can tell you for sure though that I feel exactly the same as I did on a carbohydrate diet now, except I don’t need any carbs for low intensity rides and feel that my energy levels are exactly the same after a long steady ride as when I start (my overall fitness is down compared to usual however, as I’ve not been able to put the hours in this year so far). If I had to guess I’d say that despite your body having available ketones, you are still low on glycogen reserves and perhaps you are still needing to burn a relatively high proportion of carbs at 20 minute power intensity. For me that seemed to fix itself some time between 6 – 12 weeks into the diet, although as I mentioned I did back off a bit from a ketogenic diet so may have prolonged things. For some more info take a look at this blog post (these guys seem to be at the forefront of coaching for cyclists & triathletes in ketosis):

      Their well trained cyclists (who probably already do a ton of base miles so would likely already be good fat burners on a carbohydrate diet) did find 15 minute power was lower, so that might always be the case.

      If you don’t mind risking coming out of ketosis you could experiment with bringing carbs back in during high intensity efforts – it’s something I plan to do and was the option they found worked best for the study above.

      Lastly, I suspect you are going to Mallorca mainly to get some big miles in (ie base training) so if that’s the case then I’d try to stay in ketosis if I was you, as you won’t be getting anywhere near 20 min power except for maybe one or two exceptions? (San Salvador would be one!)

      Hope this helps and let me know how you get on!

  2. Hi Kevin, thanks for the information. I’ve had a quick look at the link but I will have a proper read later, it’s not a site I’d come across before.
    You’re right about Majorca and I’ll be doing mainly long steady rides. The temptation to have a beer after will be huge though.
    I’ll certainly let you know how I get on, if you want to check out my strava I’m the Terry Williamson that lives in Newcastle upon Tyne.

    1. Hi Terry, just wondered how you got on in Mallorca? I had a look on Strava and think I found you but you have set your profile to private so I can’t see your rides…

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