Keto Diet and Cycling and Bonking

I have been on a Keto diet for over 2 years now. Still trying to get a better understanding of how it effect endurance cycling. Back when eating a normal diet I learned how eating a couple power bars on a ride would prevent the glycogen bonk.

I am now having a couple F Bombs on a ride which helps with calories and electrolyte drops and also some of the Nuun tablets. What I feel like I am getting a variant of an electolyte bonk over longer distances. Anyone having similar experience or suggestions for foods on long distance riding.

I have been on a keto diet since the summer, and done a reasonable (but certainly not extensive) amount of research on some of this. So, please take everything I say with (at least) a grain of salt. Iā€™m sure there are others who will have some different insights.

One thing I want to get out right up-front, though, is that what you are really striving for is not to be ā€˜on a keto dietā€™ but to be ā€˜fat adaptedā€™. Once youā€™re fat adapted (which I would guess you are, if youā€™ve been following a reasonably strict keto diet), your body should convert fat into ketones easily, and then use those for fuel (at least once any sugar you have floating around is used up, since your body will always try to use up any available glucose first).

Now that I have reached a point where my body is fat adapted, I find that I can do rides up to about 100 miles without needing any food during the ride (and have even done a few starting from a fasted state, so I didnā€™t even have any nutritional fat in my system). I do drink a couple of bottles of ZipFizz along the way (very few calories, but plenty of electrolytes), and always bring a pack of nuts (mixed almonds, walnuts, pecans) along with me, plus a Clif Gel for ā€˜emergenciesā€™ (thankfully I have not needed it).

This is a good source for training while fat adapted.

Thatā€™s a pretty good book, and a quick read. I would recommend adding ā€˜The Art and Science of Low Carbohydrate Livingā€™ (same authors) as a supplement to this, as the ā€˜Performanceā€™ book refers to it regularly. (The ā€˜Performanceā€™ book almost seems like a companion book to the ā€˜Livingā€™ book.)

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Anything you notice when running low on electrolytes or has the Zip Fizz had you covered. I am pretty sure I am fat adapted but just seem to get that bonk feel, but I am pretty sure it is from electrolytes.

I had read that exercise while fat adapted allows for a more consistent aerobic endurance effort but as soon as you get to anaerobic effort, the benefits are lost.
Do you find that your rides up to threshold are ok but you bonk with a more strenuous effort?

Iā€™m not sure how extensively this has been tested, but what I have read seems to indicate that you may actually perform better at all levels once fully fat-adapted. (The shortcoming in most studies is that they are short in duration, so the test subjects do not actually get fully fat-adapted.) I donā€™t really do much in the way of sprints these days, but I will say anecdotally that I have had some of my fastest times up some local climbs since going keto. If nothing else, I definitely have not lost any performance.

Have you lost significant weight since going keto?

When I first started, and was trying to figure it all out with regard to what to eat, and when (as I am doing intermittent fasting, also), as well as get my system ā€˜balanced outā€™, I dropped nearly 15 pounds. Now, about 8 months later, I am back to about the same weight I was. Of course, I havenā€™t been as diligent on the eating as I was at the start (and Iā€™ve been hitting the weights a bit more, also), so I might be able to drop a few pounds. Iā€™m trying to be careful about that, though, because I had a body scan in the middle of this (DexaFit) when I was about midway between the two ends of my weight range, and found that I was at 8% body fat. so, I really canā€™t lose much more without either starting into the ā€˜unhealthyā€™ range, or losing muscle mass (which isnā€™t something Iā€™m particularly interested in doing).

There is truly a lot to learn and understand about keto (and athletic performance on keto) as it is generally the opposite of what we have all learned growing up: Carbs good! Fat bad! And itā€™s also not just about the macronutrient composition of the foods, but also the quality (eggs generally good, but eggs from pasture-raised chickens are superior to caged, corn-fed chickens. Same with beef. And butter. And so on.)

Also, and this is perhaps the really tough part: everyone is different. So, what works for me may not work for you. So, thereā€™s a lot of experimenting to be done.

Edit: Most of the weight that I lost initially was likely just water weight, due to burning up some excess carbs, as well as not having enough salt in my diet (which the Standard American Diet - SAD - says to cut back on - because of the high glucose - but which you need to increase on a ketogenic diet - since youā€™re shedding glucose). I started to get the weight back when I figured the balance.

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Years ago I did an extensive period of the Atkins diet. Cycling was not difficult but it was different. Took a few minutes to get the fat burning going but once accomplished, seemed like I could ride forever. Lost a lot ā€œSnapā€ in the musclesā€¦I would not want to sprint. And I am not sprinter anyway, a straight diesel kind of riderā€¦low and slow.

I would think it would be difficult to race on this kind of diet. I finally gave up on the diet as it was too limiting. Lost a bunch of weight though.

I was about 210 lbs and dropped to about 185-190 with just the cutting of the carbs. I bought a Kickr Core in October and that got me off my plateau. Should be able to get to my goal of 175. Just still have that old logic in my head of carbs for cycling. Just need to do some more longer rides to figure out the best new foods.

I was actually thinking about your ā€˜bonkingā€™ earlier this morning. I wanted to mention that keeping your electrolytes up during non-riding times is important, also. As I mentioned previously, when you cut the carbs from your diet your body wonā€™t retain as much sodium, so you may find that being a little more generous with the salt on a regular basis might help you out on your rides. Itā€™s all a bit of an experiment as to what works for you, of course, but I wanted to throw this out there.

I have dropped over 65lbs on keto. Just going keto doesnā€™t make you lose weight you still have to reduce calories.I will say that Zwifting on reduced calories does have a big impact on my ability to go more than an hour.I have bumped my calories back up to try and gain more muscle and have been able to stay at the same weight and I can go for longer rides.

Hi Iā€™ve tried keto and intermittent fasting before but dropped the ball a bit. I just started zwift and have never been fit in my life - like I walk a lot but have never done anything requiring exertion. Anyway so Iā€™m trying to cycle just over 3km twice a day at a cadence of like ~85 in whatever gear seems reasonable and my heart rate sky rockets (like 185 max 160 ave). I would go further but I start getting a bit tired because Iā€™m unfit (like not my legs - more overall tired). Anyway I had a bit of a cheat-o start but now Iā€™m getting into keto again and Iā€™m managing 20:4 intermittent fasting - Historically I like the IF because even if I slightly overshoot carbs, after fasting youā€™re probably close to keto anyway.

But this cycling is clearly anaerobic even if my exertion levels donā€™t feel like Iā€™m definitely doing max exertion (like I can still crack a joke at 185 bpm) and I know that keto is better suited to endurance and weight training etc. Is there a better time to eat or would any of you recommend say including a carrot or some extra carbs at meals to make this more sustainable?

Iā€™m 36, Female, BMI close to 24, and am mostly trying to lose some fat weight before a holiday but obviously would like to feel good and improve fitness (My VO2 max is pretty abysmal - dropped from 42 to 36) and maybe build a bit of muscle (Iā€™m eating lots of protein but not a lot fat)

Any tips would be appreciated

Hello @Ayan_Booyens and welcome to the forums!

This seems concerning to me, a very short distance and your heart rate spiking like that with what you feel is not ā€œmax exertionā€. Maybe the HRM is not reading correctly?

How long is it taking you to get to 3 km? Perhaps focusing on time would be a better metric rather than distance?

That is an ambitious goal if you havenā€™t worked up to it yet, but sounds like you have done it in the past so maybe it is easy for you. You may find that timing your workout an hour or 2 after you eat is the best, but this will come down to you experimenting with a few N=1 trials. I donā€™t think you need to add a bunch of carbs to cycle only 3 km, your ā€œtiredā€ or low energy feeling is probably due to caloric restriction more than anything.

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Like 5 to 10 minutes which is really convenient from time-management pov haha. Yeah so I record heart rate on a garmin venu watch and then the bike-tacx setup sends other stuff like cardence to zwift so I record the thing twice to see all the metrics but stuff like distance is off between the two (like 3km on garmin but 3.5 km on zwift). Anyway so besides the minor irritation of recording stuff twice, Iā€™m doubting the accuracy of this little watch and might just buy a heart strap instead, though it seems like pretty extreme kit for a beginner.

But even with gym aerobics classes when I was younger/leaner I always found long durations strenuous so maybe I just have a like small heart or something (or Iā€™ve just never been fit).

I looked up an old school friend of mine whoā€™s like an olympics level pro cyclist and I see that on race days her heart rate and cadence is similar to what Iā€™m going at (though obvs 4x power and like for an hour) but then thatā€™s her doing competitive racing and not just goofing along to look better in a swimsuit - so I donā€™t think Iā€™m going to keel over but maybe I should go for a slower cadence and stiffer gear or something instead. And yeah - check HR by comparing it to something reliable.

Thanks :slight_smile:

I think youā€™re right. Like I want to do any ā€˜more strenuousā€™ exercise in the morning because if I exercise heavily too late in the day I battle to fall asleep. But my typical eating window is after lunch till maybe 5 or 6pm. So when I cycle at 7pm I feel strong and always go a bit faster or further but then in the mornings when I want those endorphins or whatever, I end up feeling a bit tired or weak.

I originally went for the 2x 3km sessions because I once had a 3km commute and I was surprised at how rapidly my fitness improved (also I start getting tired after 3km). But maybe Iā€™ll bear with it for a week or 2 (to improve fitness) and then take advantage of still being allowed to work from home and just do one slightly longer session at like 4pm.

Thanks :slight_smile:

What is your cooling situation like, do you have a nice strong fan blowing on high power right at you when you ride?

@Ayan_Booyens are you also restricting calories? The ketogenic diet and intermittent fasting are not at all about restricting calories, just about restricting carbs (especially processed carbs) and the amount of time during the day when you are consuming calories.

Also, if you are trying to stay in ketosis, the best time to consume any carbs would be right after you exercise. Carbs at this time will not cause as large of an increase in insulin production as they would at other times of the day. Additionally, if you are restricting your carbs to a pretty low level, be sure you are increasing your salt intake. Carbs will cause your body to retain salt, and salt will cause your body to retain water. So, when you cut the carbs you will, effectively, lose a bunch of water weight (the primary reason people who go to keto tend to lose a lot of weight at the outset, but donā€™t see that loss continue). And this depletion of salt and water might also be one of the causes of feeling tired.

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Ayan, I donā€™t see in your post about the intensity or how many watts your ride is.
My comment will be generic.
Keto and cycling require careful goal matching.
The typical road ride is not well suited to a keto diet because fats are not good energy sources for high strenuous or intense activities.
In this case, you should just slow down.start off riding a pace that is comfortable for 20 - 30 min. ( Or the time you want to ride).
Another alternative is to ride and continue low carb but not keto.

Bonking hurts Either decrease intensity or increase carbs.
With cycling, you may not need such strict carb reduction.

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