Exercise without Carbs? Can Cyclists use a Ketogenic Diet?

Cycling Ascents - Accommodation and Training Camps at the foot of Alpe d'Huez

As I alluded to in my last post, I’ve come back to an interesting diet that I tried a few years back.  Before all who know me exclaim “why would you want to lose weight???”, the primary goal for this diet isn’t weight loss but to experiment with an alternative ‘fuel’ to carbs – historically I’ve often had stomach issues at one point during the sportives round here, which happen to take about 6 – 8 hours for me.  I’ve done a lot of them by now, and a common theme is that 5 – 6 hours in, my stomach rebels against all the sugary liquid, gels, and bars I’m stuffing down my neck.  By that point I’m usually reduced to just drinking water, which means that the last portion of my ride is a gamble between serious stomach discomfort vs bonking massively.

Fuel for La Marmotte
All of this is out for the time being!

This time of year is ideal to try this new diet out (I’ll get into what it involves later) as it’s the ‘off season’ – a good time of year to be trying new things out.  Why would you want to consider something other than carbs as a fuel?  Well even if we’re fully topped up, most athletes can store about a maximum of 1500 calories of glycogen (the fuel the body produces from carbs) in their muscles and liver, compared to between 30,000 – 100,000 calories of fat.  Effectively, fat is an unlimited fuel source (unless you are a seriously ‘Ultra’ athlete), so the more use you can make of it the better.

So why the diet?  Well, it turns out that carbs are what the body prefers to burn.  Give it a choice (like most people too!) and it will reach for the sugar topped chocolate filled pastry. If you supply all the carbs it might need, all of the time, it won’t go near burning any fat (why would it need to bother?)  This is fine, until your 1500 calories run out, or your stomach refuses to go on digesting…

For those of you who are now thinking – but fat burning only happens in zone 1, doesn’t it? (i.e. really easy, recovery levels of effort), and I can’t be done with really long rides going that slow! – well that’s because you’ve convinced your body that burning fat is a bad idea!  So as soon as you very slightly pick up the pace from an easy effort, your body crosses over from burning fat to burning carbs.  But you can change this ‘crossover’ point by how you train, and how you eat.

The avantage of moving the crossover point higher up towards more intense levels of effort is that you can burn less glycogen for a given effort, therefore saving it for when you need it, and also allowing you to ride longer (using fat as a fuel).  This is actually a big part of what you are trying to achieve via ‘base’ training – long steady rides will trigger the same effect, though probably to a lesser extent (along with a bunch of other stuff like blood capillary density, aerobic capacity etc).  For anyone planning on a long distance sportive, Ironman, or any aerobic activity taking more than 5 hours or so then this could potentially offer an advantage in that once fat – adapted, nutrition during events is much simpler.

So if you’re sold on becoming an unstoppable fat-burning machine, how do you do it?  Well, basically by significantly reducing the glycogen levels in your body therefore forcing your body to burn fat instead.  I won’t go into detail about the diet side of this – there are plenty of sites out there that you can check out – just search for LCHF (low carb high fat) or Keto (Ketosis) diets – this is one that I’ve used a lot, which has loads of recipes and advice.  Basically, you need to keep to a calorie intake proportion of about 20% protein, 75% fat, and 5% or less from carbs.  Yes, you read that correctly – 75% fat!  This basically means ditching the potatoes / pasta / rice, and adding more veggies / salad, and A LOT of dressing / rich sauces / butter / olive oil.  To start with, upping the fat intake to the required level is difficult to get your head around, but the recipes you can find online really help.

One of the other tricky parts is to getting your body (also your brain!) to switch over to using fat as a fuel for the first time, and if you don’t quite manage it and keep bouncing between the two you won’t get any of the benefit, and also feel like crap (just search for ‘Keto Flu’).  This highlights the fact that you need to commit to this diet – if you occasionally scoff the odd baguette or pint of beer (yes sorry no beer!, but you can have the occasional whisky or spirit) you’ll ruin the whole effect.  The one time you can sneak a few carbs in however is immediately after a hard workout (seems like if you burn them off and replace a few it doesn’t do too much harm).  Have too many though and you are back into the no mans land of feeling rough with no energy – not burning fat and very low on carbs.

For anyone who’s worried that eating all that fat pretty much flies in the face of the conventional dietary advice of the last 30 – 40 years, you might have heard by now that the tide is turning and the war on fat which started in the late 70’s early 80’s was based on some very dodgy science.   There are now lots of studies and articles are out there contradicting the low fat message. Having said that, if you want to play really safe try to mostly have non saturated fats like olive oil and fatty fish, but the case for saturated fats causing all the problems they used to be blamed with seems to be slowly disappearing.

So what’s it been like, denying myself beer, bread, pasta, pretty much any conventional dessert, CHOCOLATE MUESLI (yes you read that right….I can’t have my most favourite of all food groups, chocolate muesli!!!).  In fact the addiction to chocolate muesli was a bit of a trigger for me to start this diet – if you look at some of the videos and articles on the Diet Doctor site, you’ll see how many scientists are now agreeing that carbs are pretty much the enemy – addictive, non satiating (ie don’t fill you up), probable causes or major contributors of a lot of the biggest current western health issues like obesity, diabetes, heart disease etc.  The fact that I was struggling to walk past the muesli without taking another handful made me think that I had to prove to myself I could stop eating it for a month at least.  And it’s been hard – the first two weeks were the toughest, and the point at which I called it a day on the diet the last two times.  I just couldn’t resist a crispy baguette, or a bowl of you know what…and while it’s much better now a month in I’m still salivating a little just writing this!

But the benefits (to me personally) have been:

  • no energy / sugar slumps (not feeling tired after lunch, or even a long ride). In fact I can concentrate and energy levels are good all day, no problems, which is big improvement for me
  • much more positive mental attitude – before I could have patches where I was grumpy, a little depressed, or generally feeling my mood swinging up and down.  That’s pretty much gone, and I’m feeling good nearly all the time
  • not feeling hungry between meals, urge to snack has pretty much gone
  • weight loss – yes, yes, I know I don’t need it, and if any of my family read this they will be in shock at the idea of me weighing less – but I am a cyclist after all, and in addition to that I live in the mountains so anything more than 7-10% fat is just slowing me down!
  • ability to skip meals if required – not a big deal but with tens of thousands of calories to burn there is no problem missing a meal and certainly no ‘hangriness’
  • other health improvements – I started having IBS like symptoms a while back, and was diagnosed with a mild case of ulcerative colitis a year ago.  In the past, the symptoms from this would come and go, seemingly based on my diet, stress levels and a number of other things, but for the first time since trying to change some of these factors of my lifestyle I can really feel a difference as a result of this new diet, where other changes left me unsure if they were helping.

However what you really want to know is – will it make you faster on the bike?  Well I’m afraid you’ll have to wait for another blog post for the answer to that one.  It’s generally acknowledged that athletic performance declines when starting this diet, and current understanding (not scientifically tested) is that it might take in the order of 6 weeks to get back to a performance level where you started.  Ok so I know that’s not exactly the kind of performance improvement (i.e. zero) that will make you want to jump up and pour all your beer down the sink and start chugging back olive oil, but I’m in it for the long haul.  Hopefully I’ll turn from carb dependant to a fat burning athlete, not needing much in the way of fuel during really long rides, with a massive aerobic performance improvement (well I can hope, can’t I?)

What I can tell you from my own experience so far is that I’ve done rides of slightly sub threshold efforts (at a little lower power than usual) for 1 – 1 1/2 hours, or zone 2 – 3 rides of up to two hours without any sports drinks or carbs (just electrolyte drinks).  My breathing for a given power / effort level seems a little easier, and my sprinting power seems unchanged (still nothing to write home about, but at least not any worse!).  I haven’t tried a good threshold effort for a significant duration yet, but to be honest at this time of year that probably wouldn’t go well whatever I was eating.  Stay tuned to see how Zwift races go for me – hopefully I’ll be up to some in a week or two.  I’m hoping that long term (and by that I mean at least up till Christmas!) I’ll have encouraged my body to burn significantly more fat for a given effort, and if things seem to be going in the right direction I’ll see how far I can push the ‘no fuel’ rides.  If it means that I won’t ever need to eat a gel again, and suffer the consequent stomach cramps, it will be well worth it!

You can read more about how a ketogenic diet has worked out for me here:

Part 2 – Cycling on a low carb diet update

Part 3 – Will ketosis make me a better cyclist?

7 Replies to “Exercise without Carbs? Can Cyclists use a Ketogenic Diet?”

  1. A very illuminating Epistle from Number ONE Son.This is a far cry from your Carb based lunch of Kev Pie whilst at school in the days of yore.Best of luck as an Ironman,and 6 trips up and down Alpe d’Huez for charity,but where do you get six hours of fat from a stick-person??.

    1. Ha! I’ve not eaten Kev Pie in a long time…however don’t forget that even stick thin people have 30,000 calories of fat! (I suspect I have more than that :))

  2. Kevin, you can still enjoy chocolate – just stick to the 90% cocoa versions as they are very low on carbs and sugar. Wee tip – start your day with Keto Coffee – use Bulletproof Cooffe (high fat content and lots of other good things for you) plus 2Tblsp each of butter (Kerrygold is the best), coconut oil and heavy cream – blend and it’s awesome and gives you a massive fat boost as does 1 avocado a day.

  3. Hi Gordon, It’s the chocolate muesli that I was hooked on….which is definitely off the list! However I can now look at it without any cravings whatsoever…sugar was way tougher to beat than caffeine! I do have a bit of chocolate now and then – 90% is a bit much for me though, I don’t really like the taste so I tend to stick to 80% when I’ve been good enough 🙂

  4. LOL! Yeah, it’s the sugar cravings that still haunt me. My weakness was Krispy Kreme donuts – good grief they’re everywhere!!! Funny how cutting something out suddenly seems to make it appear all over the place! I’ve shifted to ‘carb cycling’ meaning every two weeks I have a carb day. However, I feel really crap the next day and it takes me 2/3 days to get back into ketolysis. Intermittent fasting is a good friend!

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